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Oracle® XML Developer's Kit Programmer's Guide
11g Release 2 (11.2)

Part Number E10708-02
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11 Using the XML SQL Utility (XSU)

This chapter contains these topics:

Introduction to the XML SQL Utility (XSU)

XML SQL Utility (XSU) is an XDK component that enables you to transfer XML data through Oracle SQL statements. You can use XSU to perform the following tasks:

This section contains the following topics:

Prerequisites

This chapter assumes that you are familiar with the following technologies:

  • Oracle Database SQL. XSU transfers XML to and from a database through SELECT statements and DML.

  • PL/SQL. The XDK supplies a PL/SQL API for XSU that mirrors the Java API.

  • Java Database Connectivity (JDBC). Java applications that use XSU to transfer XML to and from a database require a JDBC connection.

XSU Features

XSU has the following key features:

  • Dynamically generates DTDs or XML schemas.

  • Generates XML documents in their string or DOM representations.

  • Performs simple transformations during generation such as modifying default tag names for each <ROW> element. You can also register an XSL transformation that XSU applies to the generated XML documents as needed.

  • Generates XML as a stream of SAX2 callbacks.

  • Supports XML attributes during generation, which enables you to specify that a particular column or group of columns maps to an XML attribute instead of an XML element.

  • Allows SQL to XML tag escaping. Sometimes column names are not valid XML tag names. To avoid this problem you can either alias all the column names or turn on tag escaping.

  • Supports XMLType columns in objects or tables.

  • Inserts XML into relational database tables or views. When given an XML document, XSU can also update or delete records from a database object.

XSU Restrictions

Note the following restrictions when using XSU:

  • XSU can only store data in a single table. You can store XML across tables, however, by using the Oracle XSLT processor to transform a document into multiple documents and inserting them separately. You can also define views over multiple tables and perform insertions into the views. If a view is non-updatable (because of complex joins), then you can use INSTEAD OF triggers over the views to perform the inserts.

  • You cannot use XSU to load XML data stored in attributes into a database schema, but you can use an XSLT transformation to change the attributes into elements.

  • By default XSU is case sensitive. You can either use the correct case or specify that case should be ignored.

  • XSU cannot generate a relational database schema from an input DTD.

  • Inserting into XMLType tables using XSU is not supported. XMLType columns are supported.

Using the XML SQL Utility: Overview

This section contains the following topics:

Using XSU: Basic Process

XSU is accessible through the following interfaces:

  • The OracleXMLQuery and OracleXMLSave Java classes in the oracle.xml.sql.query package. Use the OracleXMLQuery class to generate XML from relational data and OracleXMLSave class to perform DML.

  • The PL/SQL packages DBMS_XMLQuery and DBMS_XMLSave, which mirror the Java classes.

You can write the following types of XSU applications:

  • Java programs that run inside the database and access the internal XSU Java API

  • Java programs that run on the client and access the client-side XSU Java API

  • PL/SQL programs that access XSU through PL/SQL packages

Generating XML with the XSU Java API: Basic Process

The OracleXMLQuery class makes up the XML generation part of the XSU Java API. Figure 11-1 illustrates the basic process for generating XML with XSU.

The basic steps in Figure 11-1 are as follows:

Figure 11-1 Generating XML with XSU

Description of Figure 11-1 follows
Description of "Figure 11-1 Generating XML with XSU"

  1. Create a JDBC connection to the database. Normally, you establish a connection with the DriverManager class, which manages a set of JDBC drivers. After the JDBC drivers are loaded, call getConnection(). When it finds the right driver, this method returns a Connection object that represents a database session. All SQL statements are executed within the context of this session.

    You have the following options:

    • Create the connection with the JDBC OCI driver. The following code fragment illustrates this technique:

      // import the Oracle driver class
      import oracle.jdbc.*;
      // load the Oracle JDBC driver
      DriverManager.registerDriver(new oracle.jdbc.OracleDriver());     
      // create the connection
      Connection conn =
         DriverManager.getConnection("jdbc:oracle:oci:@","hr","password");
      

      The preceding example uses the default connection for the JDBC OCI driver.

    • Create the connection with the JDBC thin driver. The thin driver is written in pure Java and can be called from any Java program. The following code fragment illustrates this technique:

      Connection conn =        
         DriverManager.getConnection("jdbc:oracle:thin:@dlsun489:1521:ORCL",
           "hr","password");
      

      The thin driver requires the host name (dlsun489), port number (1521), and the Oracle SID (ORCL). The database must have an active TCP/IP listener.

    • Use default connection used by the server-side internal JDBC driver. This driver runs within a default session and default transaction context. You are already connected to the database; your SQL operations are part of the default transaction. Thus, you do not need to register the driver. Create the Connection object as follows:

      Connection conn = new oracle.jdbc.OracleDriver().defaultConnection ();
      

    Note:

    OracleXMLDataSetExtJdbc is used only for Oracle JDBC, whereas OracleXMLDataSetGenJdbc is used for non-Oracle JDBC. These classes are in the oracle.xml.sql.dataset package.
  2. Create an XML query object and assign it a SQL query. You create an OracleXMLQuery Class instance by passing a SQL query to the constructor, as shown in the following example:

    OracleXMLQuery qry = new OracleXMLQuery (conn, "SELECT * from EMPLOYEES");
    
  3. Configure the XML query object by invoking OracleXMLQuery methods. The following example specifies that only 20 rows should be included in the result set:

    xmlQry.setMaxRows(20); 
    
  4. Return a DOM object or string by invoking OracleXMLQuery methods. For example, obtain a DOM object as follows:

    XMLDocument domDoc = (XMLDocument)qry.getXMLDOM();
    

    Obtain a string object as follows:

    String xmlString = qry.getXMLString();
    
  5. Perform additional processing on the string or DOM as needed.

    See Also:

Performing DML with the XSU Java API: Basic Process

Use the OracleXMLSave class to insert, update, and delete XML in the database. Figure 11-2 illustrates the basic process.

Figure 11-2 Storing XML in the Database Using XSU

Description of Figure 11-2 follows
Description of "Figure 11-2 Storing XML in the Database Using XSU"

The basic steps in Figure 11-2 are as follows:

  1. Create a JDBC connection to the database. This step is identical to the first step described in "Generating XML with the XSU Java API: Basic Process".

  2. Create an XML save object and assign it a table on which to perform DML. Pass a table or view name to the constructor, as shown in the following example:

    OracleXMLSave sav = new OracleXMLSave(conn, "employees");
    
  3. Specify the primary key columns. For example, the following code specifies that employee_id is the key column:

    String [] keyColNames = new String[1];
    keyColNames[0] = "EMPLOYEE_ID";
    sav.setKeyColumnList(keyColNames);
    
  4. Configure the XML save object by invoking OracleXMLSave methods. The following example specifies an update of the salary and job_id columns:

    String[] updateColNames = new String[2];
    updateColNames[0] = "SALARY";
    updateColNames[1] = "JOB_ID";
    sav.setUpdateColumnList(updateColNames); // set the columns to update
    
  5. Invoke the insertXML(), updateXML(), or deleteXML() methods on the OracleXMLSave object. The following example illustrates an update:

    // Assume that the user passes in this XML document as the first argument
    sav.updateXML(sav.getURL(argv[0]));
    

    When performing the DML, XSU performs the following tasks:

    1. Parses the input XML document.

    2. Matches element names to column names in the target table or view.

    3. Converts the elements to SQL types and binds them to the appropriate statement.

  6. Close the OracleXMLSave object and deallocate all contexts associated with it, as shown in the following example:

    sav.close();
    

    See Also:

Generating XML with the XSU PL/SQL API: Basic Process

The XSU PL/SQL API reflects the Java API in the generation and storage of XML documents from and to a database. DBMS_XMLQuery is the PL/SQL package that reflects the methods in the OracleXMLQuery Java class. This package has a context handle associated with it. Create a context by calling one of the constructor-like functions to get the handle and then use the handle in all subsequent calls.

Note:

For improved performance, consider using the C-based DBMS_XMLGEN, which is written in C and built into the database, rather than DBMS_XMLQUERY.

XSU supports the XMLType datatype. Using XSU with XMLType is useful if, for example, you have XMLType columns in objects or tables.

Generating XML results in a CLOB that contains the XML document. To use DBMS_XMLQuery and the XSU generation engine, follow these basic steps:

  1. Declare a variable for the XML query context and a variable for the generated XML. For example:

    v_queryCtx  DBMS_XMLQuery.ctxType;
    v_result    CLOB;
    
  2. Obtain a context handle by calling the DBMS_XMLQuery.newContext function and supplying it the query, either as a CLOB or a VARCHAR2. The following example registers a query to select the rows from the employees table with the WHERE clause containing the bind variables :EMPLOYEE_ID and :FIRST_NAME:

    v_queryCtx = DBMS_XMLQuery.newContext('SELECT * FROM employees 
                       WHERE employee_id=:EMPLOYEE_ID AND first_name=:FIRST_NAME');
    
  3. Bind values to the query. The binds work by binding a name to the position. clearBindValues clears all the bind variables, whereas setBindValue sets a single bind variable with a string value. For example, bind the employee_id and first_name values as shown:

    DBMS_XMLQuery.setBindValue(v_queryCtx,'EMPLOYEE_ID',20);
    DBMS_XMLQuery.setBindValue(v_queryCtx,'FIRST_NAME','John');
    
  4. Configure the query context. Set optional arguments such as the ROW tag name, the ROWSET tag name, or the number of rows to fetch, and so on. The following example specifies changes the default ROWSET element name to EMPSET:

    DBMS_XMLQuery.setRowSetTag(v_queryCtx,'EMPSET');
    
  5. Fetch the results. You can obtain the XML as a CLOB with the getXML function, which generates XML with or without a DTD or XML schema. The following example applies bind values to the statement and gets the result corresponding to the predicate employee_id = 20 and first_name = 'John':

    v_result := DBMS_XMLQuery.getXML(v_queryCtx);
    
  6. Process the results of the XML generation. For example, suppose that your program declared the following variables:

    v_xmlstr VARCHAR2(32767);
    v_line   VARCHAR2(2000);
    

    You can print the CLOB stored in v_result as follows:

    v_xmlstr := DBMS_LOB.SUBSTR(v_result,32767);
    LOOP
      EXIT WHEN v_xmlstr IS NULL;
      v_line := substr(v_xmlstr,1,INSTR(v_xmlstr,CHR(10))-1);
      DBMS_OUTPUT.PUT_LINE('| ' || v_line);
      v_xmlstr := SUBSTR(v_xmlstr,INSTR(v_xmlstr,CHR(10))+1);
    END LOOP;
    
  7. Close the context. For example:

    DBMS_XMLQuery.closeContext(v_queryCtx);
    

Performing DML with the PL/SQL API: Basic Process

DBMS_XMLSave is the PL/SQL package that reflects the methods in the OracleXMLSave Java class. This package has a context handle associated with it. Create a context by calling one of the constructor-like functions to get the handle and then use the handle in all subsequent calls.

To use DBMS_XMLSave, follow these basic steps:

  1. Declare a variable for the XML save context and a variable for the number of rows touched by the DML. For example:

    savCtx DBMS_XMLSave.ctxType;
    v_rows   NUMBER;
    
  2. Create a context handle by calling the DBMS_XMLSave.newContext function and supply it the table name to use for the DML operations.

    savCtx  := DBMS_XMLSave.newContext('hr.employees');
    
  3. Set options based on the type of DML that you want to perform.

    For inserts you can set the list of columns to insert into the setUpdateColumn function. The default is to insert values into all columns. The following example sets five columns in the employees table:

    DBMS_XMLSave.setUpdateColumn(savCtx,'EMPLOYEE_ID'); 
    DBMS_XMLSave.setUpdateColumn(savCtx,'LAST_NAME');
    DBMS_XMLSave.setUpdateColumn(savCtx,'EMAIL');
    DBMS_XMLSave.setUpdatecolumn(savCtx,'JOB_ID');
    DBMS_XMLSave.setUpdateColumn(savCtx,'HIRE_DATE');
    

    For updates you must supply the list of key columns. Optionally, you can then supply the list of columns for update. In this case, the tags in the XML document matching the key column names will be used in the WHERE clause of the UPDATE statement and the tags matching the update column list will be used in the SET clause of the UPDATE statement. For example:

    DBMS_XMLSave.setKeyColumn(savCtx,'employee_id'); -- set key column
    -- set list of columns to update.
    DBMS_XMLSave.setUpdateColumn(savCtx,'salary');
    DBMS_XMLSave.setUpdateColumn(savCtx,'job_id');
    

    For deletes the default is to create a WHERE clause to match all the tag values present in each <ROW> element of the document supplied. To override this behavior, set the list of key columns. In this case only those tag values whose tag names match these columns are used to identify the rows to delete (in effect used in the WHERE clause of the DELETE statement). For example:

    DBMS_XMLSave.setKeyColumn(savCtx,'EMPLOYEE_ID');
    
  4. Supply a context and XML document to the insertXML, updateXML, or deleteXML functions. For example:

    v_rows := DBMS_XMLSave.deleteXML(savCtx,xmlDoc);
    
  5. Repeat the DML any number of times if needed.

  6. Close the context. For example:

    DBMS_XMLSave.closeContext(savCtx);
    

For a model use the Java examples described in "Programming with the XSU Java API".

Installing XSU

XSU is included in the Oracle Database software CD along with the other XDK utilities. "Java XDK Component Dependencies" describes the XSU components and dependencies.

By default, the Oracle Universal Installer installs XSU on disk and loads it into the database. No user intervention is required. If you did not load XSU in the database when installing Oracle, you can install XSU manually as follows:

  1. Make sure that Oracle XML DB is installed.

  2. Load the xsu12.jar file into the database. This JAR file, which has a dependency on xdb.jar for XMLType access, is described in Table 3-1.

  3. Run the $ORACLE_HOME/rdbms/admin/dbmsxsu.sql script. This SQL script builds the XSU PL/SQL API.

As explained in "Using XSU: Basic Process", you do not have to load XSU into the database in order to use it. XSU can reside in any tier that supports Java.

The following sections describe your installation options:

Installing XSU in the Database

Figure 11-3 shows the typical architecture for applications that use the XSU libraries installed in the database. XML generated from XSU running in the database can be placed in advanced queues in the database to be queued to other systems or clients. You deliver the XML internally through stored procedures in the database or externally through web or application servers.

In Figure 11-3 all lines are bidirectional. Because XSU can generate as well as save data, resources can deliver XML to XSU running inside the database, which can then insert it in the appropriate database tables.

Figure 11-3 Running XSU in the Database

Description of Figure 11-3 follows
Description of "Figure 11-3 Running XSU in the Database"

Installing XSU in an Application Server

Your application architecture may need to use an application server in the middle tier. The application tier can be an Oracle database, Oracle application server, or a third-party application server that supports Java programs.

You can generate XML in the middle tier from SQL queries or ResultSets for various reasons, for example, to integrate different JDBC data sources in the middle tier. In this case, you can install the XSU in your middle tier, thereby enabling your Java programs to make use of XSU through its Java API.

Figure 11-4 shows a typical architecture for running XSU in a middle tier. In the middle tier, data from JDBC sources is converted by XSU into XML and then sent to Web servers or other systems. Again, the process is bidirectional, which means that the data can be put back into the JDBC sources (database tables or views) by means of XSU. If an Oracle database itself is used as the application server, then you can use the PL/SQL front-end instead of Java.

Figure 11-4 Running XSU in the MIddle Tier

Description of Figure 11-4 follows
Description of "Figure 11-4 Running XSU in the MIddle Tier"

Installing XSU in a Web Server

Figure 11-5 shows that XSU can live in the Web server as long as the Web server supports Java servlets. In this way you can write Java servlets that use XSU. XSQL Servlet is a standard servlet provided by Oracle. It is built on top of XSU and provides a template-like interface to XSU functionality. To perform XML processing in the Web server and avoid intricate servlet programming, you can use the XSQL Servlet.

Figure 11-5 Running XSU in a Web Server

Description of Figure 11-5 follows
Description of "Figure 11-5 Running XSU in a Web Server"

See Also:

Running the XSU Demo Programs

Demo programs for XSU are included in $ORACLE_HOME/xdk/demo/java/xsu. Table 11-1 describes the XML files and programs that you can use to test XSU.

Table 11-1 XSU Sample Files

File Description

bindSQLVariables.sql

An PL/SQL script that binds values for EMPLOYEE_ID and FIRST_NAME to columns in the employees table. Refer to "Binding Values in XSU".

changeElementName.sql

A PL/SQL program that obtains the first 20 rows of the employees table as an XML document. Refer to "Specifying Element Names with DBMS_XMLQuery".

createObjRelSchema.sql

A SQL script that sets up an object-relational schema and populates it. Refer to "XML Mapping Against an Object-Relational Schema".

createObjRelSchema2.sql

A SQL script that sets up an object-relational schema and populates it. Refer to "Altering the Database Schema or SQL Query".

createRelSchema.sql

A SQL script that creates a relational table and then creates a customer view that contains a customer object on top of it. Refer to "Altering the Database Schema or SQL Query".

customer.xml

An XML document that describes a customer. Refer to "Altering the Database Schema or SQL Query".

deleteEmployeeByKey.sql

A PL/SQL program that deletes an employee by primary key. Refer to "Deleting by Key with DBMS_XMLSave: Example".

deleteEmployeeByRow.sql

A PL/SQL program that deletes an employee by row. Refer to "Deleting by Row with DBMS_XMLSave: Example".

domTest.java

A program that generates a DOM tree and then traverses it in document order, printing the nodes one by one. Refer to "Generating a DOM Tree with OracleXMLQuery".

index.txt

A README that describes the programs in the demo directory.

insProc.sql

A PL/SQL program that inserts an XML document into a table. Refer to "Inserting Values into All Columns with DBMS_XMLSave".

insertClob.sql

A SQL script that creates a table called xmldocument and stores an XML document in the table as a CLOB. Refer to "Inserting Values into All Columns with DBMS_XMLSave".

insertClob2.sql

A SQL script that inserts an XML document into the xmldocument table. Refer to "Inserting into a Subset of Columns with DBMS_XMLSave".

insertClob3.sql

A SQL script that inserts an XML document into the xmldocument table. Refer to "Updating with Key Columns with DBMS_XMLSave".

insertClob4.sql

A SQL script that inserts an XML document into the xmldocument table. Refer to "Specifying a List of Columns with DBMS_XMLSave: Example".

insertEmployee.sql

A PL/SQL script that calls the insProc stored procedure and inserts an employee into the employees table. Refer to "Inserting XML with DBMS_XMLSave".

insertEmployee2.sql

A PL/SQL script that invokes the testInsert procedure to insert the XML data for an employee into the hr.employees table. Refer to "Inserting into a Subset of Columns with DBMS_XMLSave".

mapColumnToAtt.sql

A SQL script that queries the employees table, rendering employee_id as an XML attribute. Refer to "Altering the Database Schema or SQL Query".

new_emp.xml

An XML document that describes a new employee. Refer to "Running the testInsert Program".

new_emp2.xml

An XML document that describes a new employee. Refer to "Running the testInsertSubset Program".

noRowsTest.java

A program that throws an exception when there are no more rows. Refer to "Raising a No Rows Exception".

pageTest.java

A program that uses the JDBC ResultSet to generate XML one page at a time. Refer to "Generating Scrollable Result Sets".

paginateResults.java

A program that generates an XML page that paginates results. Refer to "Paginating Results with OracleXMLQuery: Example".

paginateResults.sql

A PL/SQL script that paginates results. It skips the first 3 rows of the employees table and then prints the rest of the rows 10 at a time by setting skipRows to 3 for the first batch of 10 rows and then to 0 for the rest of the batches. Refer to "Paginating Results with DBMS_XMLQuery".

printClobOut.sql

A PL/SQL script that prints a CLOB to the output buffer. Refer to "Generating XML from Simple Queries with DBMS_XMLQuery".

raiseException.sql

A PL/SQL script that invokes the DBMS_XMLQuery.getExceptionContent procedure. Refer to "Handling Exceptions in the XSU PL/SQL API".

refCurTest.java

A program that generates XML from the results of the SQL query defined in the testRefCur function. Refer to "Generating XML from Cursor Objects".

samp1.java

A program that queries the scott.emp table, then generates an XML document from the query results.

samp10.java

A program that inserts sampdoc.xml into the xmltest_tab1 table.

samp2.java

A program that queries the scott.emp table, then generates an XML document from the query results. This program demonstrates how you can customize the generated XML document.

sampdoc.xml

A sample XML data document that samp10.java inserts into the database.

samps.sql

A SQL script that creates the xmltest_tab1 table used by samp10.java.

simpleQuery.sql

A PL/SQL script that selects 20 rows from the hr.employees table and obtains an XML document as a CLOB. Refer to "Generating XML from Simple Queries with DBMS_XMLQuery".

testDML.sql

A PL/SQL script that uses the same context and settings to perform DML depending on user input. Refer to "Reusing the Context Handle with DBMS_XMLSave".

testDeleteKey.java

A program that limits the number of elements used to identify a row, which improves performance by caching the DELETE statement and batching transactions. Refer to "Deleting by Key with OracleXMLSave".

testDeleteKey.sql

A PL/SQL script that deletes a row from the employees table for every <ROW> element in an input XML document. Refer to "Deleting by Key with DBMS_XMLSave: Example".

testDeleteRow.java

A program that accepts an XML document filename as input and deletes the rows corresponding to the elements in the document. Refer to "Deleting by Row with OracleXMLSave".

testDeleteRow.sql

A SQL script that deletes a row from the employees table for every <ROW> element in an input XML document. Refer to "Deleting by Row with DBMS_XMLSave: Example".

testException.java

A sample program shown that throws a runtime exception and then obtains the parent exception by invoking Exception.getParentException(). Refer to "Obtaining the Parent Exception".

testInsert.java

A Java program that inserts XML values into all columns of the hr.employees table. Refer to "Inserting XML into All Columns with OracleXMLSave".

testInsert.sql

A PL/SQL script that inserts XML data into a subset of columns. Refer to "Inserting into a Subset of Columns with DBMS_XMLSave".

testInsertSubset.java

A program shown that inserts XML data into a subset of columns. Refer to "Inserting XML into a Subset of Columns with OracleXMLSave".

testRef.sql

A PL/SQL script that creates a function that defines a REF cursor and returns it. Every time the testRefCur function is called, it opens a cursor object for the SELECT query and returns that cursor instance. Refer to "Generating XML from Cursor Objects".

testUpdate.java

A sample program that updates the hr.employees table by invoking the OracleXMLSave.setKeyColumnList() method. Refer to "Updating Rows with OracleXMLSave".

testUpdateKey.sql

A PL/SQL that creates a PL/SQL procedure called testUpdateKey that uses the employee_id column of the employees table as a primary key. Refer to "Updating with Key Columns with DBMS_XMLSave".

testUpdateList.java

Suppose only want to update the salary and job title for each employee and ignore the other information. If you know that all the elements to be updated are the same for all ROW elements in the XML document, then you can use the OracleXMLSave.setUpdateColumnNames() method to specify the columns. Refer to "Updating a Column List with OracleXMLSave".

testUpdateSubset.sql

A SQL script that creates the procedure testUpdateSubset. The procedure specifies the employee_id column as the key and specifies that salary and job_id should be updated. Refer to "Specifying a List of Columns with DBMS_XMLSave: Example".

testXMLSQL.java

A sample program that uses XSU to generate XML as a String object. This program queries the hr.employees table and prints the result set to standard output. Refer to "Generating a String with OracleXMLQuery".

upd_emp.xml

An XML document that contains updated salary and other information for a series of employees. Refer to "Running the testUpdate Program".

upd_emp2.xml

An XML document that contains updated salary and other information for a series of employees. Refer to "Running the testUpdate Program".

updateEmployee.sql

An XML document that contains new data for two employees. Refer to "Running the testUpdateList Program".

updateEmployee2.sql

A PL/SQL script that passes an XML document to the testUpdateSubset procedure and generates two UPDATE statements. Refer to "Specifying a List of Columns with DBMS_XMLSave: Example".


The steps for running the demos are:

  1. Change into the $ORACLE_HOME/xdk/demo/java/xsu directory (UNIX) or %ORACLE_HOME%\xdk\demo\java\xsu directory (Windows).

  2. Make sure that your environment variables are set as described in "Setting Up the Java XDK Environment". In particular, make sure that the Java classpath includes xsu12.jar for XSU and ojdbc5.jar (Java 1.5) for JDBC. If you use a multibyte character set other than UTF-8, ISO8859-1, or JA16SJIS, then place orai18n.jar in your classpath so that JDBC can convert the character set of the input file to the database character set.

  3. Compile the Java programs as shown in the following example:

    javac samp1.java samp2.java samp10.java
    
  4. Connect to an Oracle database as hr and run the SQL script createRelSchema:

    CONNECT hr
    @$ORACLE_HOME/xdk/demo/java/xsu/createRelSchema
    

The following sections describe the XSU demos in detail.

Using the XSU Command-Line Utility

The XDK includes a command-line Java interface for XSU. XSU command-line options are provided through the Java class OracleXML. To use this API ensure that your Java classpath is set as described in "Setting Up the Java XDK Environment".

To print usage information for XSU to standard output, run the following command:

java OracleXML

To use XSU, invoke it with either the getXML or putXML parameter as follows:

java OracleXML getXML options
java OracleXML putXML options

Table 11-2 describes the getXML options.

Table 11-2 getXML Options

getXML Option Description

-user "username/password"

Specifies the username and password to connect to the database. If this is not specified, then the user defaults to scott/tiger. Note that the connect string is also specified. You can specify the username and password as part of the connect string.

-conn "JDBC_connect_string"

Specifies the JDBC database connect string. By default the connect string is: "jdbc:oracle:oci:@".

-withDTD

Instructs the XSU to generate the DTD along with the XML document.

-withSchema

Instructs the XSU to generate the schema along with the XML document.

-rowsetTag tag_name

Specifies the rowset tag, which is tag that encloses all the XML elements corresponding to the records returned by the query. The default rowset tag is <ROWSET>. If you specify an empty string ("") for rowset, then XSU omits the rowset element.

-rowTag tag_name

Specifies the row tag that encloses the data corresponding to a database row. The default row tag is <ROW>. If you specify an empty string ("") for the row tag, then XSU omits the row tag.

-rowIdAttr row_id_attribute_name

Names the attribute of the ROW element that keeps track of the cardinality of the rows. By default this attribute is num. If you specify an empty string as the rowID attribute, then XSU omits the attribute.

-rowIdColumn row_Id_column_name

Specifies that the value of one of the scalar columns from the query is to be used as the value of the rowID attribute.

-collectionIdAttr collect_id_attr_name

Names the attribute of an XML list element that keeps track of the cardinality of the elements of the list. The generated XML lists correspond to either a cursor query, or collection. If you specify an empty string ("") as the rowID attribute, then XSU omits the attribute.

-useTypeForCollElemTag

Specifies the use type name for the column-element tag. By default XSU uses the column-name_item.

-useNullAttrId

Specifies the attribute NULL (TRUE/FALSE) to indicate the nullness of an element.

-styleSheet stylesheet_URI

Specifies the stylesheet in the XML processing instruction.

-stylesheetType stylesheet_type

Specifies the stylesheet type in the XML processing instruction.

-setXSLT URI

Specifies the XSLT stylesheet to apply to the XML document.

-setXSLTRef URI

Sets the XSLT external entity reference.

-useLowerCase | -useUpperCase

Generates lowercase or uppercase tag names. The default is to match the case of the SQL object names from which the tags are generated.

-withEscaping

Specifies the treatment of characters that are legal in SQL object names but illegal in XML tags. If such a character is encountered, then it is escaped so that it does not throw an exception.

-errorTag error tag_name

Specifies the tag to enclose error messages that are formatted as XML.

-raiseException

Specifies that XSU should throw a Java exception. By default XSU catches any error and produces the XML error.

-raiseNoRowsException

Raises an exception if no rows are returned.

-useStrictLegalXMLCharCheck

Performs strict checking on input data.

-maxRows maximum_rows

Specifies the maximum number of rows to be retrieved and converted to XML.

-skipRows number_of_rows_to_skip

Specifies the number of rows to be skipped.

-encoding encoding_name

Specifies the character set encoding of the generated XML.

-dateFormat date_format

Specifies the date format for the date values in the XML document.

-fileName SQL_query_fileName | SQL_query

Specifies the file name that contains the query or the query itself.


Table 11-3 describes the putXML options.

Table 11-3 putXML Options

putXML Options Description

-user "username/password"

Specifies the username and password to connect to the database. If not specified, the user defaults to scott/tiger. The connect string is also specified; you can specify the username and password as part of the connect string.

-conn "JDBC_connect_string"

Specifies the JDBC database connect string. By default the connect string is: "jdbc:oracle:oci:@".

-batchSize batching_size

Specifies the batch size that controls the number of rows that are batched together and inserted in a single trip to the database to improve performance.

-commitBatch commit_size

Specifies the number of inserted records after which a commit is to be executed. If the autocommit is TRUE (the default), then setting commitBatch has no consequence.

-rowTag tag_name

Specifies the row tag, which is tag used to enclose the data corresponding to a database row. The default row tag is <ROW>. If you specify an empty string for the row tag, then XSU omits the row tag.

-dateFormat date_format

Specifies the date format for the date values in the XML document.

-withEscaping

Turns on reverse mapping if SQL to XML name escaping was used when generating the doc.

-ignoreCase

Makes the matching of the column names with tag names case insensitive. For example, EmpNo matches with EMPNO if ignoreCase is on.

-preserveWhitespace

Preserves the whitespace in the inserted XML document.

-setXSLT URI

Specifies the XSLT to apply to the XML document before inserting.

-setXSLTRef URI

Sets the XSLT external entity reference.

-fileName file_name | -URL URL | -xmlDoc xml_document

Specifies the XML document to insert: a local file, a URL, or an XML document as a string on the command line.

table_name

Specifies the name of the table to put the values into.


Generating XML with the XSU Command-Line Utility

To generate XML from the database schema use the getXML parameter. For example, to generate an XML document by querying the employees table in the hr schema, you can use the following syntax:

java OracleXML getXML -user "hr/password" "SELECT * FROM employees"

The preceding command performs the following tasks:

  1. Connects to the current default database

  2. Executes the specified SELECT query

  3. Converts the SQL result set to XML

  4. Prints the XML to standard output

The getXML parameter supports a wide range of options, which are explained in Table 11-2.

Generating XMLType Data with the XSU Command-Line Utility

You can use XSU to generate XML from tables with XMLType columns. Suppose that you run the demo script setup_xmltype.sql to create and populate the parts table. You can generate XML from this table with XSU as follows:

java OracleXML getXML -user "hr/password" -rowTag "Part" "SELECT * FROM parts"

The output of the command is shown below:

<?xml version = '1.0'?>
<ROWSET>
   <Part num="1">
      <PARTNO>1735</PARTNO>
      <PARTNAME>Gizmo</PARTNAME>
      <PARTDESC>
         <Description>
           <Title>Description of the Gizmo</Title>
           <Author>John Smith</Author>
           <Body>
             The <b>Gizmo</b> is <i>grand</i>.
           </Body>
         </Description>
      </PARTDESC>
   </Part>
</ROWSET>

Performing DML with the XSU Command-Line Utility

To insert an XML document called new_employees.xml into the hr.employees table, use the following syntax:

java OracleXML putXML -user "hr/password" -fileName "new_employees.xml" employees

The preceding command performs the following tasks:

  1. Connects to the current database as hr

  2. Reads the XML document named new_emp.xml

  3. Parses the XML document, matching the tags with column names

  4. Inserts the values appropriately into the employees table

The getXML parameter supports a wide range of options, which are explained in Table 11-2.

Programming with the XSU Java API

This section contains the following topics:

Generating a String with OracleXMLQuery

The testXMLSQL.java demo program uses XSU to generate XML as a String object. This program queries the hr.employees table and prints the result set to standard output.

The testXMLSQL.java program follows these steps:

  1. Register the JDBC driver and create a database connection. The following code fragment uses the OCI JDBC driver and connects with the username hr:

    import oracle.jdbc.*;...Connection conn  = getConnection("hr","password");
    ...
    private static Connection getConnection(String username, String password)
        throws SQLException
    {
    // register the JDBC driver
      DriverManager.registerDriver(new oracle.jdbc.OracleDriver()); 
    // create the connection using the OCI driver
      Connection conn =
        DriverManager.getConnection("jdbc:oracle:oci:@",username,password);
      return conn;
    }
    
  2. Create an XML query object and initialize it with a SQL query. The following code fragment initializes the object with a SELECT statement on hr.employees:

    OracleXMLQuery qry = new OracleXMLQuery(conn, "SELECT * FROM employees");
    
  3. Obtain the query result set as a String object. The getXMLString() method transforms the object-relational data specified in the constructor into an XML document. The following example illustrates this technique:

    String str = qry.getXMLString();
    
  4. Close the query object to release any resources, as shown in the following code:

    qry.close();
    

Running the testXMLSQL Program

To run the testXMLSQL.java program perform the following steps:

  1. Compile testXMLSQL.java with javac.

  2. Execute java testXMLSQL on the command line.

You must have the CLASSPATH pointing to this directory for the Java executable to find the class. Alternatively, use visual Java tools such as Oracle JDeveloper to compile and run this program. When run, this program prints out the XML file to the screen. The following shows sample output with some rows edited out:

<?xml version = '1.0'?>
<ROWSET>
   <ROW num="1">
      <EMPLOYEE_ID>100</EMPLOYEE_ID>
      <FIRST_NAME>Steven</FIRST_NAME>
      <LAST_NAME>King</LAST_NAME>
      <EMAIL>SKING</EMAIL>
      <PHONE_NUMBER>515.123.4567</PHONE_NUMBER>
      <HIRE_DATE>6/17/1987 0:0:0</HIRE_DATE>
      <JOB_ID>AD_PRES</JOB_ID>
      <SALARY>24000</SALARY>
      <DEPARTMENT_ID>90</DEPARTMENT_ID>
   </ROW>
<!-- ROW num="2" through num="107" ... -->
</ROWSET>

Generating a DOM Tree with OracleXMLQuery

To generate a DOM tree from the XML generated by XSU, you can directly request a DOM document from XSU. This technique saves the overhead of creating a string representation of the XML document and then parsing it to generate the DOM tree.

XSU calls the Oracle XML parser to construct the DOM tree from the data values. The domTest.java demo program generates a DOM tree and then traverses it in document order, printing the nodes one by one.

The first two steps in the domTest.java program are the same as for the testXMLSQL.java program described in "Generating a String with OracleXMLQuery". The program proceeds as follows:

  1. Obtain the DOM by invoking getXMLDOM() method. The following example illustrates this technique:

    XMLDocument domDoc = (XMLDocument)qry.getXMLDOM();
    
  2. Print the DOM tree. The following code prints to standard output:

    domDoc.print(System.out);
    

    You can also create a StringWriter and wrap it in a PrintWriter as follows:

    StringWriter s = new StringWriter(10000);
    domDoc.print(new PrintWriter(s));
    System.out.println(" The string version ---> \n"+s.toString());
    

After compiling the program, run it from the command line as follows:

java domTest

Paginating Results with OracleXMLQuery

This section contains the following topics:

Limiting the Number of Rows in the Result Set

In testXMLSQL.java and domTest.java, XSU generated XML from all rows returned by the query. Suppose that you query a table that contains 1000 rows, but you want only 100 rows at a time. One approach is to execute one query to obtain the first 100 rows, another to obtain the next 100 rows, and so on. With this technique you cannot skip the first five rows of the query and then generate the result. To avoid these problems, use the following Java methods:

  • OracleXMLSave.setSkipRows() forces XSU to skip the desired number of rows before starting to generate the result. The command-line equivalent to this method is the -skipRows parameter.

  • OracleXMLSave.setMaxRows() limits the number of rows converted to XML. The command-line equivalent to this method is the -maxRows parameter.

Example 11-1 sets skipRows to a value of 5 and maxRows to a value of 1, which causes XSU to skip the first 5 rows and then generate XML for the next row when querying the hr.employees table.

Example 11-1 Specifying skipRows and maxRows on the Command Line

java OracleXML getXML -user "hr/password" -skipRows 5 -maxRows 1 \
  "SELECT * FROM employees"

The following shows sample output (only row 6 of the query result set is returned):

<?xml version = '1.0'?>
<ROWSET>
   <ROW num="6">
      <EMPLOYEE_ID>105</EMPLOYEE_ID>
      <FIRST_NAME>David</FIRST_NAME>
      <LAST_NAME>Austin</LAST_NAME>
      <EMAIL>DAUSTIN</EMAIL>
      <PHONE_NUMBER>590.423.4569</PHONE_NUMBER>
      <HIRE_DATE>6/25/1997 0:0:0</HIRE_DATE>
      <JOB_ID>IT_PROG</JOB_ID>
      <SALARY>4800</SALARY>
      <MANAGER_ID>103</MANAGER_ID>
      <DEPARTMENT_ID>60</DEPARTMENT_ID>
   </ROW>
</ROWSET>

Keeping the Object Open for the Duration of the User's Session

In some situations you may want to keep the query object open for the duration of the user session. You can handle such cases with the maxRows() method and the keepObjectOpen() method.

Consider a Web search engine that paginates search results. The first page lists 10 results, the next page lists 10 more, and so on. To perform this task with XSU, request 10 rows at a time and keep the ResultSet open so that the next time you ask XSU for more results, it starts generating from where the last generation finished. If OracleXMLQuery creates a result set from the SQL query string, then it typically closes the ResultSet internally because it assumes no more results are required. Thus, you should invoke keepObjectOpen() to keep the cursor active.

A different case requiring an open query object is when the number of rows or number of columns in a row is very large. In this case, you can generate multiple small documents rather than one large document.

Paginating Results with OracleXMLQuery: Example

The paginateResults.java program shows how you can generate an XML page that paginates results. The output XML displays only 20 rows of the hr table.

The first step of the paginateResults.java program, which creates the connection, is the same as in testXMLSQL.java. The program continues as follows:

  1. Create a SQL statement object and initialize it with a SQL query. The following code fragment sets two options in java.sql.ResultSet:

    Statement stmt = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, 
                                          ResultSet.CONCUR_READ_ONLY);
    
  2. Create the query as a string and execute it by invoking Statement.executeQuery(). The return object is of type ResultSet. The following example illustrates this technique:

    String sCmd = "SELECT first_name, last_name FROM hr.employees"; 
    ResultSet rs = stmt.executeQuery(sCmd); 
    
  3. Create the query object, as shown in the following code:

    OracleXMLQuery xmlQry = new OracleXMLQuery(conn, rs);
    
  4. Configure the query object. The following code specifies that the query object should be open for the duration of the session. It also limits the number of rows returned to 20:

    xmlQry.keepObjectOpen(true); 
    xmlQry.setRowsetTag("ROWSET"); 
    xmlQry.setRowTag("ROW"); 
    xmlQry.setMaxRows(20); 
    
  5. Retrieve the result as a String and print:

    String sXML = xmlQry.getXMLString(); 
    System.out.println(sXML);
    

After compiling the program, run it from the command line as follows:

java paginateResults

Generating Scrollable Result Sets

In some situations you may want to perform a query and then retrieve a previous page of results from within the result set. To enable scrolling, instantiate the Oracle.jdbc.ResultSet class. You can use the ResultSet object to move back and forth within the result set and use XSU to generate XML each time.

The pageTest.java program shows how to use the JDBC ResultSet to generate XML a page at a time. Using ResultSet may be necessary in cases that are not handled directly by XSU, for example, when setting the batch size and binding values.

The pageTest.java program creates a pageTest object and initializes it with a SQL query. The constructor for the pageTest object performs the following steps:

  1. Create a JDBC connection by calling the same getConnection() method defined in paginateResults.java:

    Connection conn;
    ...
    conn  = getConnection("hr","password");
    
  2. Create a statement as follows:

    Statement stmt;
    ...
    stmt = conn.createStatement();
    
  3. Execute the query passed to the constructor to obtain the scrollable result set. The following code illustrates this technique:

    ResultSet rset = stmt.executeQuery(sqlQuery);
    
  4. Create a query object by passing references to the connection and result set objects to the constructor. The following code fragment illustrates this technique:

    OracleXMLQuery qry;
    ...
    qry = new OracleXMLQuery(conn,rset); 
    
  5. Configure the query object. The following code fragment specifies that the query object should be kept open and that it should raise an exception when there are no more rows:

    qry.keepObjectOpen(true);
    qry.setRaiseNoRowsException(true);
    qry.setRaiseException(true);
    
  6. After creating the query object by passing it the string "SELECT * FROM employees", the program loops through the result set. The getResult() method receives integer values specifying the start row and end row of the set. It sets the maximum number of rows to retrieve by calculating the difference of these values and then retrieves the result as a string. The following while loop retrieves and prints ten rows at a time:

    int i = 0;
    while ((str = test.getResult(i,i+10))!= null)
    {
      System.out.println(str);
      i+= 10;
    }
    

After compiling the program, run it from the command line as follows:

java pageTest

Generating XML from Cursor Objects

The OracleXMLQuery class provides XML conversion only for query strings or ResultSet objects. If your program uses PL/SQL procedures that return REF cursors, then how do you perform the conversion? You can use the ResultSet conversion mechanism described in "Generating Scrollable Result Sets".

REF cursors are references to cursor objects in PL/SQL. These cursor objects are SQL statements over which a program can iterate to obtain a set of values. The cursor objects are converted into OracleResultSet objects in the Java world. In your Java program you can initialize a CallableStatement object, execute a PL/SQL function that returns a cursor variable, obtain the OracleResultSet object, and then send it to the OracleXMLQuery object to obtain the desired XML.

Consider the testRef PL/SQL package defined in the testRef.sql script. It creates a function that defines a REF cursor and returns it. Every time the testRefCur PL/SQL function is called, it opens a cursor object for the SELECT query and returns that cursor instance. To convert the object to XML, do the following:

  1. Run the testRef.sql script to create the testRef package in the hr schema.

  2. Compile and run the refCurTest.java program to generate XML from the results of the SQL query defined in the testRefCur function.

To apply the stylesheet, you can use the applyStylesheet command, which forces the stylesheet to be applied before generating the output.

Inserting Rows with OracleXMLSave

To insert a document into a table or view, supply the table or view name and then the document. XSU parses the document (if a string is given) and then creates an INSERT statement into which it binds all the values. By default XSU inserts values into all columns of the table or view. An absent element is treated as a NULL value. The following example shows how you can store the XML document generated from the hr.employees table in the table.

Inserting XML into All Columns with OracleXMLSave

The testInsert.java demo program inserts XML values into all columns of the hr.employees table.

The program follows these steps:

  1. Create a JDBC OCI connection. The program calls the same getConnection() method used by the previous examples in this chapter:

    Connection conn = getConnection("hr","password");
    
  2. Create an XML save object. You initialize the object by passing it the Connection reference and the name of the table on which you want to perform DML. The following example illustrates this technique:

    OracleXMLSave sav = new OracleXMLSave(conn, "employees");
    
  3. Insert the data in an input XML document into the hr.employees table. The following code fragment creates a URL from the document filename specified on the command line:

    sav.insertXML(sav.getURL(argv[0]));
    
  4. Close the XML save object as follows:

    sav.close();
    
Running the testInsert Program

Assume that you write the new_emp.xml document to describe new employee Janet Smith, who has employee ID 7369. You pass the filename new_emp.xml as an argument to the testInsert program as follows:

java testInsert "new_emp.xml"

The program inserts a new row in the employees table that contains the values for the columns specified. Any absent element inside the row element is treated as NULL.

Running the program generates an INSERT statement of the following form:

INSERT INTO hr.employees 
  (employee_id, first_name, last_name, email, phone_number, hire_date, 
   salary, commission_pct, manager_id, department_id)
VALUES
  (?, ?, ?, ?, ?, ?, ?, ?, ?, ?);     

XSU matches the element tags in the input XML document that match the column names and binds their values.

Inserting XML into a Subset of Columns with OracleXMLSave

In some circumstances you may not want to insert values into all columns. For example, the group of values that you obtain may not be the complete set, requiring you to use triggers or default values for the remaining columns. The testInsertSubset.java demo program shows how to handle this case.

The program follows these steps:

  1. Create a JDBC OCI connection. The program calls the same getConnection() method used by the previous examples in this chapter:

    Connection conn = getConnection("hr","password");
    
  2. Create an XML save object. Initialize the object by passing it the Connection reference and the name of the table on which you want to perform DML. The following example illustrates this technique:

    OracleXMLSave sav = new OracleXMLSave(conn, "employees");
    
  3. Create an array of strings. Each element of the array should contain the name of a column in which values will be inserted. The following code fragment specifies the names of five columns:

    String [] colNames = new String[5];
    colNames[0] = "EMPLOYEE_ID";
    colNames[1] = "LAST_NAME";
    colNames[2] = "EMAIL";
    colNames[3] = "JOB_ID";
    colNames[4] = "HIRE_DATE";
    
  4. Configure the XML save object to update the specified columns. The following statement passes a reference to the array to the OracleXMLSave.setUpdateColumnList() method:

    sav.setUpdateColumnList(colNames);
    
  5. Insert the data in an input XML document into the hr.employees table. The following code fragment creates a URL from the document filename specified on the command line:

    sav.insertXML(sav.getURL(argv[0]));
    
  6. Close the XML save object as follows:

    sav.close();
    
Running the testInsertSubset Program

Assume that you use the new_emp2.xml document to store data for new employee Adams, who has employee ID 7400. You pass new_emp2.xml as an argument to the testInsert program as follows:

java testInsert new_emp2.xml

The program ignores values for the columns that were not specified in the input file. It performs an INSERT for each ROW element in the input and batches the INSERT statements by default.

The program generates the following INSERT statement:

INSERT INTO hr.employees (employee_id, last_name, email, job_id, hire_date) 
  VALUES (?, ?, ?, ?, ?);

Updating Rows with OracleXMLSave

To update the fields in a table or view, supply the table or view name and then the XML document. XSU parses the document (if a string is given) and then creates one or more UPDATE statements into which it binds all the values. The following examples show how you can use an XML document to update the hr.employees table.

Updating with Key Columns with OracleXMLSave

The testUpdate.java demo program updates the hr.employees table by invoking the OracleXMLSave.setKeyColumnList() method.

The testUpdate.java program follows these steps:

  1. Create a JDBC OCI connection. The program calls the same getConnection() method used by the previous examples in this chapter:

    Connection conn = getConnection("hr","password");
    
  2. Create an XML save object. You initialize the object by passing it the Connection reference and the name of the table on which you want to perform DML. The following example illustrates this technique:

    OracleXMLSave sav = new OracleXMLSave(conn, "employees");
    
  3. Create a single-element String array to hold the name of the primary key column in the table to be updated. The following code fragment specifies the name of the employee_id column:

    String [] keyColNames = new String[1];
    colNames[0] = "EMPLOYEE_ID";
    
  4. Set the XML save object to the primary key specified in the array. The following statement passes a reference to the keyColNames array to the OracleXMLSave.setKeyColumnList() method:

    sav.setKeyColumnList(keyColNames);
    
  5. Update the rows specified in the input XML document. The following statement creates a URL from the filename specified on the command line:

    sav.updateXML(sav.getURL(argv[0]));
    
  6. Close the XML save object as follows:

    sav.close();
    
Running the testUpdate Program

You can use XSU to update specified fields in a table. Example 11-2 shows upd_emp.xml, which contains updated salary and other information for the two employees that you just added, 7369 and 7400.

Example 11-2 upd_emp.xml

<?xml version='1.0'?>
<ROWSET>
 <ROW num="1">
    <EMPLOYEE_ID>7400</EMPLOYEE_ID>
    <SALARY>3250</SALARY>
 </ROW>
 <ROW num="2">
    <EMPLOYEE_ID>7369</EMPLOYEE_ID>
    <JOB_ID>SA_REP</JOB_ID>
    <MANAGER_ID>145</MANAGER_ID>
 </ROW>
<!-- additional rows ... -->
</ROWSET>

For updates, supply XSU with the list of key column names in the WHERE clause of the UPDATE statement. In the hr.employees table the employee_id column is the key.

Pass the filename upd_emp.xml as an argument to the preceding program as follows:

java testUpdate upd_emp.xml

The program generates two UPDATE statements. For the first ROW element, the program generates an UPDATE statement to update the SALARY field as follows:

UPDATE hr.employees SET salary = 3250 WHERE employee_id = 7400;

For the second ROW element the program generates the following statement:

UPDATE hr.employees SET job_id = 'SA_REP' AND MANAGER_ID = 145 
  WHERE employee_id = 7369;

Updating a Column List with OracleXMLSave

You may want to update a table by using only a subset of the elements in an XML document. You can achieve this goal by specifying a list of columns. This technique speeds processing because XSU uses the same UPDATE statement with bind variables for all the ROW elements. You can also ignore other tags in the XML document.

Note:

When you specify a list of columns to update, if an element corresponding to one of the update columns is absent, XSU treats it as NULL.

Suppose you want to update the salary and job title for each employee and ignore the other data. If you know that all the elements to be updated are the same for all ROW elements in the XML document, then you can use the OracleXMLSave.setUpdateColumnNames() method to specify the columns. The testUpdateList.java program illustrates this technique.

The testUpdateList.java program follows these steps:

  1. Create a JDBC OCI connection. The program calls the same getConnection() method used by the previous examples in this chapter:

    Connection conn = getConnection("hr","password");
    
  2. Create an XML save object. You initialize the object by passing it the Connection reference and the name of the table on which you want to perform DML. The following example illustrates this technique:

    OracleXMLSave sav = new OracleXMLSave(conn, "employees");
    
  3. Create an array of type String to hold the name of the primary key column in the table to be updated. The array contains only one element, which is the name of the primary key column in the table to be updated. The following code fragment specifies the name of the employee_id column:

    String [] colNames = new String[1];
    colNames[0] = "EMPLOYEE_ID";
    
  4. Set the XML save object to the primary key specified in the array. The following statement passes a reference to the colNames array to the OracleXMLSave.setKeyColumnList() method:

    sav.setKeyColumnList(keyColNames);
    
  5. Create an array of type String to hold the name of the columns to be updated. The following code fragment specifies the name of the employee_id column:

    String[] updateColNames = new String[2];
    updateColNames[0] = "SALARY";
    updateColNames[1] = "JOB_ID";
    
  6. Set the XML save object to the list of columns to be updated. The following statement performs this task:

    sav.setUpdateColumnList(updateColNames);
    
  7. Update the rows specified in the input XML document. The following code fragment creates a URL from the filename specified on the command line:

    sav.updateXML(sav.getURL(argv[0]));
    
  8. Close the XML save object as follows:

    sav.close();
    
Running the testUpdateList Program

Suppose that you use the sample XML document upd_emp2.xml to store new data for employees Steven King, who has an employee ID of 100, and William Gietz, who has an employee ID of 206. You pass upd_emp2.xml as an argument to the testUpdateList program as follows:

java testUpdateList upd_emp2.xml

In this example, the program generates two UPDATE statements. For the first ROW element, the program generates the following statement:

UPDATE hr.employees SET salary = 8350 AND job_id = 'AC_ACCOUNT' 
  WHERE employee_id = 100;

For the second ROW element the program generates the following statement:

UPDATE hr.employees SET salary = 25000 AND job_id = 'AD_PRES' 
  WHERE employee_id = 206;

Deleting Rows with OracleXMLSave

When deleting from XML documents, you can specify a list of key columns. XSU uses these columns in the WHERE clause of the DELETE statement. If you do not supply the key column names, then XSU creates a new DELETE statement for each ROW element of the XML document. The list of columns in the WHERE clause of the DELETE statement matches those in the ROW element.

Deleting by Row with OracleXMLSave

The testDeleteRow.java demo program accepts an XML document filename as input and deletes the rows corresponding to the elements in the document.

The testDeleteRow.java program follows these steps:

  1. Create a JDBC OCI connection. The program calls the same getConnection() method used by the previous examples in this chapter:

    Connection conn = getConnection("hr","password");
    
  2. Create an XML save object. You initialize the object by passing it the Connection reference and the name of the table on which you want to perform DML. The following example illustrates this technique:

    OracleXMLSave sav = new OracleXMLSave(conn, "employees");
    
  3. Delete the rows specified in the input XML document. The following code fragment creates a URL from the filename specified on the command line:

    sav.deleteXML(sav.getURL(argv[0]));
    
  4. Close the XML save object as follows:

    sav.close();
    
Running the testDelete Program

Suppose that you want to delete the employees 7400 and 7369 that you added in "Inserting Rows with OracleXMLSave".

To make this example work correctly, connect to the database and disable a constraint on the hr.job_history table:

CONNECT hr
ALTER TABLE job_history
  DISABLE CONSTRAINT JHIST_EMP_FK;
EXIT

Now pass upd_emp.xml to the testDeleteRow program as follows:

java testDeleteRow upd_emp.xml

The program forms the DELETE statements based on the tag names present in each ROW element in the XML document. It executes the following statements:

DELETE FROM hr.employees WHERE salary = 3250 AND employee_id = 7400;
DELETE FROM hr.employees WHERE job_id = 'SA_REP' AND MANAGER_ID = 145 
  AND employee_id = 7369;

Deleting by Key with OracleXMLSave

To only use the key values as predicates on the DELETE statement, invoke the OracleXMLSave.setKeyColumnList() method. This approach limits the number of elements used to identify a row, which has the benefit of improving performance by caching the DELETE statement and batching transactions. The testDeleteKey.java program illustrates this technique.

The testDeleteKey.java program follows these steps:

  1. Create a JDBC OCI connection. The program calls the same getConnection() method used by the previous examples in this chapter:

    Connection conn = getConnection("hr","password");
    
  2. Create an XML save object. You initialize the object by passing it the Connection reference and the name of the table on which you want to perform DML. The following example illustrates this technique:

    OracleXMLSave sav = new OracleXMLSave(conn, "employees");
    
  3. Create an array of type String to hold the name of the primary key column in the table. The array contains only one element. The following code fragment specifies the name of the employee_id column:

    String [] colNames = new String[1];
    colNames[0] = "EMPLOYEE_ID";
    
  4. Set the XML save object to the primary key specified in the array. The following statement passes a reference to the colNames array to the OracleXMLSave.setKeyColumnList() method:

    sav.setKeyColumnList(keyColNames);
    
  5. Delete the rows specified in the input XML document. The following code fragment creates a URL from the filename specified on the command line:

    sav.deleteXML(sav.getURL(argv[0]));
    
  6. Close the XML save object as follows:

    sav.close();
    
Running the testDeleteKey Program

Suppose that you want to delete employees 7400 and 7369 that you added in "Updating with Key Columns with OracleXMLSave". Note that if you already deleted these employees in the previous example, you can first add them back to the employees table as follows:

java testInsert new_emp.xml
java testInsert new_emp2.xml

Delete employees 7400 and 7369 by passing the same upd_emp.xml document to the testDeleteRow program as follows:

java testDeleteKey upd_emp.xml

The program forms the following single generated DELETE statement:

DELETE FROM hr.employees WHERE employee_id=?;

The program executes the following DELETE statements, one for each employee:

DELETE FROM hr.employees WHERE employee_id = 7400;
DELETE FROM hr.employees WHERE employee_id = 7369;

Handling XSU Java Exceptions

XSU catches all exceptions that occur during processing and throws oracle.xml.sql.OracleXMLSQLException, which is a generic runtime exception. The calling program does not have to catch this exception if it can still perform the appropriate action. The exception class provides methods to obtain error messages and also get any existing parent exception.

Obtaining the Parent Exception

The testException.java demo program throws a runtime exception and then obtains the parent exception by invoking Exception.getParentException().

Running the preceding program generates the following error message:

Caught SQL Exception:ORA-00904: "SD": invalid identifier

Raising a No Rows Exception

When there are no rows to process, XSU returns a null string. You can throw an exception every time there are no more rows, however, so that the program can process this exception through exception handlers. When a program invokes OracleXMLQuery.setRaiseNoRowsException(), XSU raises an oracle.xml.sql.OracleXMLSQLNoRowsException whenever there are no rows to generate for the output. This is a runtime exception and need not be caught.

The noRowsTest.java demo program instantiates the pageTest class defined in pageTest.java. The condition to check the termination changed from checking whether the result is null to an exception handler.

The noRowsTest.java program creates a pageTest object and initializes it with a SQL query. The program proceeds as follows:

  1. Configure the query object or raise a no rows exception. The following code fragment illustrates this technique:

    pageTest test = new pageTest("SELECT * from employees");
    ...
    test.qry.setRaiseNoRowsException(true);
    
  2. Loop through the result set infinitely, retrieving ten rows at a time. When no rows are available, the program throws an exception. The following code fragment calls pageTest.nextPage(), which scrolls through the result set ten rows at a time:

    try
    {
      while(true)
        System.out.println(test.nextPage());
    }
    
  3. Catch the no rows exception and print "END OF OUTPUT". The following code illustrates this technique:

    catch(oracle.xml.sql.OracleXMLSQLNoRowsException e)
    {
      System.out.println(" END OF OUTPUT "); 
      try
      {
        test.close();
      }
      catch ( Exception ae )
      {
        ae.printStackTrace(System.out);
      }
    }
    

After compiling the program, run it from the command line as follows:

java noRowsTest

Programming with the XSU PL/SQL API

This chapter contains the following topics:

Note:

For increased performance, consider using DBMS_XMLGen and DBMS_XMLStore as alternatives to DBMS_XMLQuery and DBMS_XMLSave. The two former packages are written in C and are built in to the database kernel. You can also use SQL/XML functions such as XML_Element for XML access in the database.

Generating XML from Simple Queries with DBMS_XMLQuery

This section shows how you can use the DBMS_XMLQuery package to generate XML from a SQL query. To make the example work, connect to the database as hr and run the printClobOut.sql script. The script creates printClobOut, which is a simple procedure that prints a CLOB to the output buffer. If you run the printClobOut procedure in SQL*Plus, it prints the input CLOB to the screen. Set server output to ON to see the results. You may have to increase your display buffer to see all the output.

Run the simpleQuery.sql script to select 20 rows from the hr.employees table and obtain an XML document as a CLOB. The program first gets the context handle by passing in a query and then calls the getXML function to obtain the CLOB value. The document is in the same encoding as the database character set. This sample application assumes that you created the printClobOut procedure by running printClobOut.sql.

Specifying Element Names with DBMS_XMLQuery

With the XSU PL/SQL API you can change the default ROW and the ROWSET element names, which are the default names placed around each row of the result and around the whole output XML document. Use the PL/SQL procedures setRowTagName and setRowSetTagName to accomplish this task.

Connect as hr and run the changeElementName.sql script in SQL*Plus to obtain the first 20 rows of the employees table as an XML document. The anonymous PL/SQL block changes the ROW and ROWSET element names to EMP and EMPSET. Note that the block calls the printClobOut procedure that you created by running printClobOut.sql.

The generated XML document has an <EMPSET> document element. Each row is separated with the <EMP> tag.

Paginating Results with DBMS_XMLQuery

You can paginate query results by calling the following PL/SQL functions:

  • setMaxRows sets the maximum number of rows to be converted to XML. This maximum is relative to the current row position from which the previous result was generated.

  • setSkipRows specifies the number of rows to skip before converting the row values to XML.

Run the paginateResult.sql script to execute an anonymous block that paginates results. It skips the first 3 rows of the employees table and prints the rest of the rows 10 at a time by setting skipRows to 3 for the first batch of 10 rows and then to 0 for the rest of the batches. For multiple fetches, you must determine when there are no more rows to fetch, which you can do by calling setRaiseNoRowsException. This procedure raises an exception if no rows are written to the CLOB. This exception can be caught and used as the termination condition.

Setting Stylesheets in XSU

The XSU PL/SQL API provides the ability to set stylesheets on the generated XML documents as follows:

  • Set the stylesheet header in the result with the setStylesheetHeader procedure. This procedure adds the XML processing instruction that includes the stylesheet.

  • Apply a stylesheet to the resulting XML document before generation. This method increases performance dramatically because otherwise the XML document must be generated as a CLOB, sent to the parser again, and have the stylesheet applied. XSU generates a DOM document, calls the parser, applies the stylesheet and then generates the result. To apply the stylesheet to the resulting XML document, use the setXSLT procedure, which uses the stylesheet to generate the result.

Binding Values in XSU

The XSU PL/SQL API provides the ability to bind values to a SQL statement. The SQL statement can contain named bind variables, which must be prefixed with a colon (:). The bindSQLVariables.sql script runs an anonymous PL/SQL block that binds values for EMPLOYEE_ID and FIRST_NAME to columns in the employees table.

Inserting XML with DBMS_XMLSave

To insert a document into a table or view, supply the table or the view name and then the XML document. XSU parses the XML document (if a string is given) and then creates an INSERT statement into which it binds all the values. By default, XSU inserts values into all the columns of the table or view and treats absent elements as NULL.

Inserting Values into All Columns with DBMS_XMLSave

Run the insProc.sql demo script to create a PL/SQL stored procedure, insProc, which accepts the following parameters:

  • An XML document as a CLOB

  • The name of the table in which to insert the document

You can invoke the insProc procedure to insert an XML document into the table.

Run the insertClob.sql script to create a table called xmldocument and store an XML document in the table as a CLOB. The XML document describes employee 7370, Liz Gardner, whom you want to insert into the hr.employees table.

Example 11-3 insertClob.sql

CREATE TABLE hr.xmldocument
  (docid   NUMBER PRIMARY KEY,
  xml_text CLOB);
-- insert an XML document into the CLOB column
INSERT INTO hr.xmldocument (docid,xml_text)
VALUES (1,
       '<?xml version="1.0"?>
       <ROWSET>
        <ROW num="1">
           <EMPLOYEE_ID>7370</EMPLOYEE_ID>
           <FIRST_NAME>Liz</FIRST_NAME>
           <LAST_NAME>Gardner</LAST_NAME>
           <EMAIL>liz.gardner@business.com</EMAIL>
           <PHONE_NUMBER>650-555-6127</PHONE_NUMBER>
           <HIRE_DATE>12/18/2004 0:0:0</HIRE_DATE>
           <SALARY>3000</SALARY>
           <COMMISSION_PCT>0</COMMISSION_PCT>
           <JOB_ID>SH_CLERK</JOB_ID>
           <MANAGER_ID>103</MANAGER_ID>
           <DEPARTMENT_ID>20</DEPARTMENT_ID>
        </ROW>
       </ROWSET>');

Run the insertEmployee.sql script shown in Example 11-4 to call the insProc stored procedure and insert Liz Gardner into the employees table.

Example 11-4 insertEmployee.sql

DECLARE
  v_xml_text CLOB;
BEGIN
  SELECT xml_text 
    INTO v_xml_text
  FROM hr.xmldocument
  WHERE docid = 1;
  insProc(v_xml_text, 'employees');
END;
/

As in "Inserting Rows with OracleXMLSave", running the callinsProc procedure generates an INSERT statement of the form shown in Example 11-5.

Example 11-5 Form of the INSERT Statement

INSERT INTO hr.employees 
  (employee_id, first_name, last_name, email, phone_number, hire_date, 
   salary, commission_pct, manager_id, department_id)
VALUES
  (?, ?, ?, ?, ?, ?, ?, ?, ?, ?);     

XSU matches the element tags in the input XML document that match the column names and binds their values.

Inserting into a Subset of Columns with DBMS_XMLSave

As explained in "Inserting XML into a Subset of Columns with OracleXMLSave", you may not want to insert values into all columns. You can create a list of column names for insert processing and pass it to the DBMS_XMLSave procedure. You can set these values by calling the setUpdateColumnName procedure repeatedly and passing in a column name to update every time. Clear the column name settings by invoking clearUpdateColumnList.

Run the testInsert.sql demo script to create a PL/SQL stored procedure called testInsert. You can use this procedure to insert XML data of type CLOB into the hr.employees table.

Run the insertClob2.sql script shown in Example 11-6 to insert an XML document describing new employee Jordan into a CLOB column of the xmldocument table. Note that the document does not contain an element corresponding to every column in the employees table.

Example 11-6 insertClob2.sql

-- insert an XML document into the CLOB column  of the xmldocument table with only 
-- some of the possible elements
INSERT INTO hr.xmldocument (docid, xml_text)
VALUES (2,
       '<?xml version="1.0"?>
       <ROWSET>
        <ROW num="1">
           <EMPLOYEE_ID>7401</EMPLOYEE_ID>
           <LAST_NAME>Jordan</LAST_NAME>
           <EMAIL>jim.jordan@business.com</EMAIL>
           <JOB_ID>SH_CLERK</JOB_ID>
           <HIRE_DATE>12/17/2004 0:0:0</HIRE_DATE>
        </ROW>
       </ROWSET>');

Running the insertEmployee2.sql script shown in Example 11-7 inserts the data for employee Jim Jordan into a subset of the columns in the hr.employees table.

Example 11-7 insertEmployee2.sql

DECLARE
  v_xml_text CLOB;
BEGIN
  SELECT xml_text 
    INTO v_xml_text
  FROM hr.xmldocument
  WHERE docid = 2;
  testInsert(v_xml_text);
END;
/

As in "Inserting XML into a Subset of Columns with OracleXMLSave", calling testInsert generates the following INSERT statement:

INSERT INTO hr.employees (employee_id, last_name, email, job_id, hire_date) 
  VALUES (?, ?, ?, ?, ?);

Updating with DBMS_XMLSave

As described in "Updating Rows with OracleXMLSave", you can use an XML document to update specified fields in a table. You can either specify a column to use as a key or pass a list of columns for updating.

Updating with Key Columns with DBMS_XMLSave

Run the testUpdateKey.sql script to create a PL/SQL procedure called testUpdateKey. This procedure uses the employee_id column of the hr.employees table as a primary key.

Run the insertClob3.sql script shown in shown in Example 11-8 to insert an XML document into the CLOB column of the xmldocument table. The document specifies a new salary for employee 7400 and a new job ID and manager ID for employee 7369.

Example 11-8 insertClob3.sql

INSERT INTO hr.xmldocument (docid, xml_text)
VALUES (3,
       '<?xml version="1.0"?>
        <ROWSET>
         <ROW num="1">
            <EMPLOYEE_ID>7400</EMPLOYEE_ID>
            <SALARY>3250</SALARY>
         </ROW>
         <ROW num="2">
            <EMPLOYEE_ID>7369</EMPLOYEE_ID>
            <JOB_ID>SA_REP</JOB_ID>
            <MANAGER_ID>145</MANAGER_ID>
         </ROW>
        </ROWSET>');

Run the updateEmployee.sql script shown in Example 11-9 to pass the XML document to the testUpdateKey procedure and generate two UPDATE statements.

Example 11-9 updateEmployee.sql

DECLARE
  v_xml_text CLOB;
BEGIN
  SELECT xml_text 
    INTO v_xml_text
  FROM hr.xmldocument
  WHERE docid = 3;
  testUpdateKey(v_xml_text);
END;
/

For the first ROW element, the program generates an UPDATE statement as follows:

UPDATE hr.employees SET salary = 3250 WHERE employee_id = 7400;

For the second ROW element the program generates the following statement:

UPDATE hr.employees SET job_id = 'SA_REP' AND MANAGER_ID = 145 
  WHERE employee_id = 7369;

Specifying a List of Columns with DBMS_XMLSave: Example

As described in "Updating a Column List with OracleXMLSave", you can specify a list of columns to update.

Run the testUpdateSubset.sql script creates the PL/SQL procedure testUpdateSubset. The procedure uses the employee_id column as key and updates only the salary and job_id columns of the hr.employees table.

Run the insertClob4.sql script to insert an XML document into the xmldocument table. The <ROW> elements in the document describe employees 100 and 206. Each <ROW> element has ten subelements that contain descriptive text.

Run the updateEmployee2.sql script shown in Example 11-10 to pass the XML CLOB to the testUpdateSubset procedure and generate two UPDATE statements.

Example 11-10 updateEmployee2.sql

DECLARE
  v_xml_text CLOB;
BEGIN
  SELECT xml_text 
    INTO v_xml_text
  FROM hr.xmldocument
  WHERE docid = 4;
  testUpdateSubset(v_xml_text);
END;
/

The procedure updates only those columns specified in the setUpdateColumn procedure, salary and email, for employees 100 and 206.

Deleting with DBMS_XMLSave

As described in "Deleting Rows with OracleXMLSave", you can supply a list of key columns that XSU uses to determine which rows to delete. XSU specifies these columns in the WHERE clause of the DELETE statement.

Deleting by Row with DBMS_XMLSave: Example

Create the testDeleteRow PL/SQL procedure by running the testDeleteRow.sql script. The procedure deletes a row from the hr.employees table for every <ROW> element in an input XML document.

Suppose that you want to delete the employee Jim Jordan that you added in Example 11-7. Run the deleteEmployeeByRow.sql script shown in Example 11-11 to pass the XML document as a CLOB to the testDeleteRow stored procedure.

Example 11-11 Deleting by Row

DECLARE
  v_xml_text CLOB;
BEGIN
  SELECT xml_text 
    INTO v_xml_text
  FROM hr.xmldocument
  WHERE docid = 2;
  testDeleteRow(v_xml_text);
END;
/

The preceding call to testDeleteRow generates the following DELETE statement:

DELETE FROM hr.employees
  WHERE employee_id = 7401 AND last_name = 'JORDAN'
  AND email = 'jim.jordan@business.com' AND job_id = 'SH_CLERK'
  AND hire_date = '12/17/2004 0:0:0';

The program forms the DELETE statements based on the tag names present in each <ROW> element in the XML document.

Deleting by Key with DBMS_XMLSave: Example

As explained in "Deleting by Key with OracleXMLSave", you can specify a column to use as a primary key for the deletions. Use the DBMS_XMLSave.setKeyColumn function to specify the key.

The testDeleteKey procedure created by running testDeleteKey.sql deletes a row from the employees table for every <ROW> element in an input XML document.

Suppose that you want to delete the employee Liz Gardner that you added in Example 11-4. Run the deleteEmployeeByKey.sql script shown in Example 11-12 to pass the XML document as a CLOB to the testDeleteKey stored procedure.

Example 11-12 Deleting by Key

DECLARE
  v_xml_text CLOB;
BEGIN
  SELECT xml_text 
    INTO v_xml_text
  FROM hr.xmldocument
  WHERE docid = 1;
  testDeleteKey(v_xml_text);
END;
/

In the preceding procedure call, XSU generates a single DELETE statement of the following form:

DELETE FROM hr.employees WHERE employee_id=?

XSU uses this statement for all ROW elements in the input XML document.

Handling Exceptions in the XSU PL/SQL API

Good PL/SQL coding practice accounts for possible exceptions. The anonymous PL/SQL block in raiseException.sql demonstrates how to invoke the DBMS_XMLQuery.getExceptionContent procedure. Run the script in SQL*Plus to print the following error message:

Exception caught 904 ORA-00904: "Z": invalid identifier

Reusing the Context Handle with DBMS_XMLSave

In the DML examples described in the preceding sections, you can use the same context handle to perform more than one operation. That is, you can perform more than one INSERT with the same context provided that all of the insertions access the same table specified when creating the save context. You can also use the same context to mix DML statements.

The testDML.sql script shows how to use the same context and settings to perform DML depending on user input. The example uses a PL/SQL supplied package static variable to store the context so that the same context can be used for all function calls.

In the testDML package created by the script, you create a context once for the whole package (and thus the session) and reuse the context for multiple DML operations.

Note:

The key column employee_id is used both for updates and deletes as a way of identifying the row.

You can call any of the three procedures created by the script to update the employees table:

testDML.insertXML(xmlclob);
testDML.deleteXML(xmlclob);
testDML.updateXML(xmlclob);

Each procedure call uses the same context, which improves the performance of these operations, particularly if these operations are performed frequently.

Tips and Techniques for Programming with XSU

This section provides additional tips and techniques for writing programs with XSU. It contains the following topics:

How XSU Maps Between SQL and XML

The fundamental component of a table is a column, whereas the fundamental components of an XML document are elements and attributes. How do tables map to XML documents? For example, if the hr.employees table has a column called last_name, how is this structure represented in XML: as an <EMPLOYEES> element with a last_name attribute or as a <LAST_NAME> element within a different root element? This section answers such questions by describing how SQL maps to XML and vice versa. It contains the following topics:

Default SQL to XML Mapping

Assume that you want to display data from some column of the hr.employees table as an XML document. You run XSU at the command line as follows:

java OracleXML getXML -user "hr/password" -withschema \
  "SELECT employee_id, last_name, hire_date FROM employees"

XSU outputs an XML document based on the input query. The root element of the document is <DOCUMENT>. The following shows sample output, with extraneous lines replaced by comments:

<?xml version = '1.0'?>
<DOCUMENT xmlns:xsd="http://www.w3.org/2001/XMLSchema">
   <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
   <!-- children of schema element ... -->
   </xsd:schema>
   <ROWSET xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:noNamespaceSchemaLocation="#/DOCUMENT/xsd:schema[not(@targetNamespace)]">
      <ROW num="1">
         <EMPLOYEE_ID>100</EMPLOYEE_ID>
         <LAST_NAME>King</LAST_NAME>
         <HIRE_DATE>6/17/1987 0:0:0</HIRE_DATE>
      </ROW>
      <!-- additional rows ... -->
   </ROWSET>
</DOCUMENT>

In the generated XML, the rows returned by the SQL query are children of the <ROWSET> element. The XML document has the following features:

  • The <ROWSET> element has zero or more <ROW> child elements corresponding to the number of rows returned. If the query generates no rows, then no <ROW> elements are included; if the query generates one row, then one <ROW> element is included, and so forth.

  • Each <ROW> element contains data from one of the table rows. Specifically, each <ROW> element has one or more child elements whose names and content are identical to the database columns specified in the SELECT statement.

XML Mapping Against an Object-Relational Schema

Assume a case in which you generate an XML document from an object-relational schema. Run the createObjRelSchema.sql script in SQL*Plus to set up and populate an object-relational schema. The schema contains a dept1 table with two columns that employ user-defined types.

You can query the dept1 table as follows by invoking XSU from the command line:

% java OracleXML getXML -user "hr/password" -withschema "SELECT * FROM dept1"

XSU returns the XML document shown in Example 11-13, which is altered so that extraneous lines are replaced by comments.

Example 11-13 XSU-Generated Sample Document

<?xml version='1.0'?>
<DOCUMENT xmlns:xsd="http://www.w3.org/2001/XMLSchema">
   <schema targetNamespace="http://xmlns.oracle.com/xdb/SYSTEM"      
           xmlns="http://www.w3.org/2001/XMLSchema"
           xmlns:SYSTEM="http://xmlns.oracle.com/xdb/SYSTEM">
   <!-- children of schema element ... -->
   </xsd:schema>
   <ROWSET xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:noNamespaceSchemaLocation="#/DOCUMENT/xsd:schema[not(@targetNamespace)]">
      <ROW num="1">
         <DEPTNO>120</DEPTNO>
         <DEPTNAME>Treasury</DEPTNAME>
         <DEPTADDR>
            <STREET>2004 Charade Rd</STREET>
            <CITY>Seattle</CITY>
            <STATE>WA</STATE>
            <ZIP>98199</ZIP>
         </DEPTADDR>
         <EMPLIST>
            <EMPLIST_ITEM>
               <EMPLOYEE_ID>1</EMPLOYEE_ID>
               <LAST_NAME>Mehta</LAST_NAME>
               <SALARY>6000</SALARY>
               <EMPLOYEE_ADDRESS>
                  <STREET>500 Main Road</STREET>
                  <CITY>Seattle</CITY>
                  <STATE>WA</STATE>
                  <ZIP>98199</ZIP>
               </EMPLOYEE_ADDRESS>
            </EMPLIST_ITEM>
         </EMPLIST>
      </ROW>
   </ROWSET>
</DOCUMENT>
 

As in the previous example, the mapping is canonical, that is, <ROWSET> contains <ROW> child elements, which in turn contain child elements corresponding to the columns in dept1. For example, the <DEPTNAME> element corresponds to the dept1.deptname column. The elements corresponding to scalar type columns contain the data from the columns.

Default Mapping of Complex Type Columns to XML

The situation is more complex with elements corresponding to a complex type column. In Example 11-13, <DEPTADDR> corresponds to the dept1.deptAddr column, which is of object type AddressType. Consequently, <DEPTADDR> contains child elements corresponding to the attributes specified in the type AddressType. The AddressType attribute street corresponds to the child XML element <STREET> and so forth. These sub-elements can contain data or subelements of their own, depending on whether the attribute they correspond to is of a simple or complex type.

Default Mapping of Collections to XML

When dealing with elements corresponding to database collections, the situation is also different. In Example 11-13, the <EMPLIST> element corresponds to the emplist column of type EmployeeListType. Consequently, the <EMPLIST> element contains a list of <EMPLIST_ITEM> elements, each corresponding to one of the elements of the collection. Note the following:

  • The <ROW> elements contain a cardinality attribute num.

  • If a particular column or attribute value is NULL, then for that row, the corresponding XML element is left out altogether.

  • If a top-level scalar column name starts with the at sign (@) character, then the column is mapped to an XML attribute instead of an XML element.

Default XML to SQL Mapping

XML to SQL mapping is the reverse of SQL to XML mapping. Consider the following differences when using XSU to map XML to SQL:

  • When transforming XML to SQL, XSU ignores XML attributes. Thus, there is really no mapping of XML attributes to SQL.

  • When transforming SQL to XML, XSU performs the mapping on a single ResultSet created by a SQL query. The query can span multiple database tables or views. When transforming XML into SQL, note the following:

    • To insert one XML document into multiple tables or views, you must create an object-relational view over the target schema.

    • If the view is not updatable, then you can use INSTEAD OF INSERT triggers.

If the XML document does not perfectly map to the target database schema, then you can perform the following actions:

  • Modify the target. Create an object-relational view over the target schema and make the view the new target.

  • Modify the XML document by using XSLT to transform the XML document. You can register the XSLT stylesheet with XSU so that the incoming XML is automatically transformed before it attempts any mapping.

  • Modify XSU's XML-to-SQL mapping. You can instruct XSU to perform case-insensitive matching of XML elements to database columns or attributes. For example, you can instruct XSU to do the following:

    • Use the name of the element corresponding to a database row instead of ROW.

    • Specify the date format to use when parsing dates in the XML document.

Customizing Generated XML

In some circumstances you may need to generate XML with a specific structure. Because the desired structure may differ from the default structure of the generated XML document, you want to have some flexibility in this process. You can customize the structure of a generated XML document by using one of the following methods:

Altering the Database Schema or SQL Query

You can perform source customizations by altering the SQL query or the database schema. The simplest and most powerful source customizations include the following:

  • In the database schema, create an object-relational view that maps to the desired XML document structure.

  • In your query, do the following:

    • Use cursor subqueries or cast-multiset constructs to create nesting in the XML document that comes from a flat schema.

    • Alias column and attribute names to obtain the desired XML element names.

    • Alias top-level scalar type columns with identifiers that begin with the at sign (@) to make them map to an XML attribute instead of an XML element. For example, executing the following statement generates an XML document in which the <ROW> element has the attribute empno:

      SELECT employee_name AS "@empno",... FROM employees;
      

Consider the customer.xml document shown in Example 11-14.

Example 11-14 customer.xml

<?xml version = "1.0"?>
<ROWSET>
 <ROW num="1">
  <CUSTOMER>
   <CUSTOMERID>1044</CUSTOMERID>
   <FIRSTNAME>Paul</FIRSTNAME>
   <LASTNAME>Astoria</LASTNAME>
   <HOMEADDRESS>
    <STREET>123 Cherry Lane</STREET>
    <CITY>SF</CITY>
    <STATE>CA</STATE>
    <ZIP>94132</ZIP>
   </HOMEADDRESS>
  </CUSTOMER>
 </ROW>
</ROWSET>

Suppose that you need to design a set of database tables to store this data. Because the XML is nested more than one level, you can use an object-relational database schema that maps canonically to the preceding XML document. Run the createObjRelSchema2.sql script in SQL*Plus to create such a database schema.

You can load the data in the customer.xml document into the customer_tab table created by the script. Invoke XSU for Java from the command line as follows:

java OracleXML putXML -user "hr/password" -fileName customer.xml customer_tab

To load customer.xml into a database schema that is not object-relational, you can create objects in views on top of a standard relational schema. For example, you can create a relational table that contains the necessary columns, then create a customer view that contains a customer object on top of it, as shown in the createRelSchema.sql script in Example 11-15.

Example 11-15 createRelSchema.sql

CREATE TABLE hr.cust_tab
 ( customerid NUMBER(10), 
   firstname VARCHAR2(20), 
   lastname VARCHAR2(20),
   street VARCHAR2(40),
   city VARCHAR2(20),
   state VARCHAR2(20),
   zip VARCHAR2(20)
 );

CREATE VIEW customer_view 
AS
SELECT customer_type(customerid, firstname, lastname,
       address_type(street,city,state,zip)) customer
FROM cust_tab;

You can load data into customer_view as follows:

java OracleXML putXML -user "hr/password" -fileName customer.xml customer_view

Alternatively, you can flatten your XML by means of XSLT and then insert it directly into a relational schema. However, this is the least recommended option.

Suppose that you want to map a particular column or a group of columns to an XML attribute instead of an XML element. To achieve this functionality, you can create an alias for the column name and prepend the at sign (@) before the name of this alias. For example, you can use the mapColumnToAtt.sql script to query the hr.employees table, rendering employee_id as an XML attribute.

You can run the mapColumnToAtt.sql script from the command line as follows:

java OracleXML getXML -user "hr/password" -fileName "mapColumnToAtt.sql"

Note:

All attributes must appear before any non-attribute.
Modifying XSU

XSU enables you to modify the rules that it uses to transform SQL data into XML. You can make any of the following changes when mapping SQL to XML:

  • Change or omit the <ROWSET> or <ROW> tag.

  • Change or omit the attribute num, which is the cardinality attribute of the <ROW> element.

  • Specify the case for the generated XML element names.

  • Specify that XML elements corresponding to elements of a collection must have a cardinality attribute.

  • Specify the format for dates in the XML document.

  • Specify that null values in the XML document have to be indicated with a nullness attribute rather then by omission of the element.

How XSU Processes SQL Statements

This section describes how XSU interacts with the database:

How XSU Queries the Database

XSU executes SQL queries and retrieves the ResultSet from the database. XSU then acquires and analyzes metadata about the ResultSet. Using the mapping described in "Default SQL to XML Mapping", XSU processes the SQL result set and converts it into an XML document.

XSU cannot handle certain types of queries, especially those that mix columns of type LONG or LONG RAW with CURSOR() expressions in the SELECT clause. LONG and LONG RAW are two examples of datatypes that JDBC accesses as streams and whose use is deprecated. If you migrate these columns to CLOBs, then the queries succeed.

How XSU Inserts Rows

When inserting the contents of an XML document into a table or view, XSU performs the following steps:

  1. Retrieves metadata about the target table or view.

  2. Generates a SQL INSERT statement based on the metadata. For example, assume that the target table is dept1 and the XML document is generated from dept1. XSU generates the following INSERT statement:

    INSERT INTO dept1 (deptno, deptname, deptaddr, emplist) VALUES (?,?,?,?)
    
  3. Parses the XML document, and for each record, it binds the appropriate values to the appropriate columns or attributes. For example, it binds the values for INSERT statement as follows:

    deptno   <- 100
    deptname <- SPORTS
    deptaddr <- AddressType('100 Redwood Shores Pkwy','Redwood Shores',
                            'CA','94065')
    emplist  <- EmployeeListType(EmployeeType(7369,'John',100000,
                AddressType('300 Embarcadero','Palo Alto','CA','94056'),...)
    
  4. Executes the statement. You can optimize INSERT processing to insert in batches and commit in batches.

How XSU Updates Rows

Updates and delete statements differ from inserts in that they can affect more than one row in the database table. For inserts, each <ROW> element of the XML document can affect at most one row in the table if no triggers or constraints are on the table. With updates and deletes, the XML element can match more than one row if the matching columns are not key columns in the table.

For update statements, you must provide a list of key columns that XSU must identify the row to update. For example, assume that you have an XML document that contains the following fragment:

<ROWSET>
  <ROW num="1">
    <DEPTNO>100</DEPTNO>
    <DEPTNAME>SportsDept</DEPTNAME>
  </ROW>
</ROWSET>

You want to change the DEPTNAME value from Sports to SportsDept. If you supply the DEPTNO as the key column, then XSU generates the following UPDATE statement:

UPDATE dept1 SET deptname = ? WHERE deptno = ?

XSU binds the values in the following way:

deptno <- 100
deptname <- SportsDept

For updates, you can also choose to update only a set of columns and not all the elements present in the XML document.

How XSU Deletes Rows

For deletes, you can choose to provide a set of key columns so that XSU can identify the rows to be deleted. If you do not provide the set of key columns, then the DELETE statement tries to match all the columns in the document. Assume that you pass the following document to XSU:

<ROWSET>
 <ROW num="1">
  <DEPTNO>100</DEPTNO>
  <DEPTNAME>Sports</DEPTNAME>
  <DEPTADDR>
      <STREET>100 Redwood Shores Pkwy</STREET>
      <CITY>Redwood Shores</CITY>
      <STATE>CA</STATE>
      <ZIP>94065</ZIP>
  </DEPTADDR>
 </ROW>
 <!-- additional rows ... -->
</ROWSET>

XSU builds a DELETE statement for each ROW element:

DELETE FROM dept1 WHERE deptno = ? AND deptname = ? AND deptaddr = ?

The binding is as follows:

deptno   <- 100
deptname <- sports
deptaddr <- addresstype('100 redwood shores pkwy','redwood city','ca',
            '94065')

How XSU Commits After DML

By default XSU performs no explicit commits. If AUTOCOMMIT is on, which is the default for a JDBC connection, then after each batch of statement executions XSU executes a COMMIT. You can override this behavior by turning AUTOCOMMIT off and then using setCommitBatch to specify the number of statement executions before XSU should commit. If an error occurs, then XSU rolls back to either the state the target table was in before the call to XSU, or the state after the last commit made during the current call to XSU.