4
Managing Oracle Objects

This chapter explains how Oracle objects work in combination with the rest of the database, and how to perform DML and DDL operations on them. It contains the following major sections:

• Privileges on Object Types and Their Methods
• Dependencies and Incomplete Types
• Synonyms for User-Defined Types
• Tools
• Utilities

Privileges on Object Types and Their Methods

Privileges for object types exist at the system level and the schema object level.

System Privileges

Oracle defines the following system privileges for object types:

• CREATE TYPE enables you to create object types in your own schema
• CREATE ANY TYPE enables you to create object types in any schema
• ALTER ANY TYPE enables you to alter object types in any schema
• DROP ANY TYPE enables you to drop named types in any schema
• EXECUTE ANY TYPE enables you to use and reference named types in any schema
• UNDER ANY TYPE enables you to create subtypes under any non-final object types
• UNDER ANY VIEW enables you to create subviews under any object view

The CONNECT and RESOURCE roles include the CREATE TYPE system privilege. The DBA role includes all of these privileges.

Schema Object Privileges

Two schema object privileges apply to object types:

• EXECUTE on an object type enables you to use the type to:
  • Define a table.
  • Define a column in a relational table.
  • Declare a variable or parameter of the named type.

  EXECUTE lets you invoke the type's methods, including the constructor.

  Method execution and the associated permissions are the same as for stored PL/SQL procedures.

• UNDER enables you to create a subtype/subview under the type/view on which the privilege is granted

  The UNDER privilege on a subtype or subview can be granted only if the grantor has the UNDER privilege on the direct supertype or superview WITH GRANT OPTION.

The phrase WITH HIERARCHY OPTION grants a specified object privilege on all subobjects of the object. This option is meaningful only with the SELECT object privilege granted on an object view in an object view hierarchy. In this case, the privilege applies to all subviews of the view on which the privilege is granted.

Using Types in New Types or Tables

In addition to the permissions detailed in the previous sections, you need specific privileges to:

• Create types or tables that use types created by other users.
• Grant use of your new types or tables to other users.

You must have the EXECUTE ANY TYPE system privilege, or you must have the EXECUTE object privilege for any type you use in defining a new type or table. You must have received these privileges explicitly, not through roles.

If you intend to grant access to your new type or table to other users, you must have either the required EXECUTE object privileges with the GRANT option or the EXECUTE ANY TYPE system privilege with the option WITH ADMIN OPTION. You must have received these privileges explicitly, not through roles.

Example

Assume that three users exist with the CONNECT and RESOURCE roles: USER1, USER2, and USER3.

USER1 performs the following DDL in the USER1 schema:

CREATE TYPE type1 AS OBJECT ( attr1 NUMBER );
CREATE TYPE type2 AS OBJECT ( attr2 NUMBER );
GRANT EXECUTE ON type1 TO user2;
GRANT EXECUTE ON type2 TO user2 WITH GRANT OPTION;

USER2 performs the following DDL in the USER2 schema:

CREATE TABLE tab1 OF user1.type1;
CREATE TYPE type3 AS OBJECT ( attr3 user1.type2 );
CREATE TABLE tab2 (col1 user1.type2 );

The following statements succeed because USER2 has EXECUTE on USER1's TYPE2 with the GRANT option:

GRANT EXECUTE ON type3 TO user3;
GRANT SELECT on tab2 TO user3;

However, the following grant fails because USER2 does not have EXECUTE on USER1.TYPE1 with the GRANT option:

GRANT SELECT ON tab1 TO user3;

USER3 can successfully perform the following actions:

CREATE TYPE type4 AS OBJECT (attr4 user2.type3);
CREATE TABLE tab3 OF type4;

Privileges on Type Access and Object Access

While object types only make use of EXECUTE privilege, object tables use all the same privileges as relational tables:

• SELECT lets you access an object and its attributes from the table.
• UPDATE lets you modify attributes of objects in the table.
• INSERT lets you add new objects to the table.
• DELETE lets you delete objects from the table.

Similar table and column privileges regulate the use of table columns of object types.

Selecting columns of an object table does not require privileges on the type of the object table. Selecting the entire row object, however, does.

Consider the following schema:

CREATE TYPE emp_type as object (
  eno    NUMBER,
  ename  CHAR(31),
  eaddr  addr_t );

CREATE TABLE emp OF emp_type;

and the following two queries:

SELECT VALUE(e) FROM emp e;
SELECT eno, ename FROM emp;

For either query, Oracle checks the user's SELECT privilege for the emp table. For the first query, the user needs to obtain the emp_type type information to interpret the data. When the query accesses the emp_type type, Oracle checks the user's EXECUTE privilege.

Execution of the second query, however, does not involve named types, so Oracle does not check type privileges.

Additionally, using the schema from the previous section, USER3 can perform the following queries:

SELECT tab1.col1.attr2 from user2.tab1 tab1;
SELECT t.attr4.attr3.attr2 FROM tab3 t;

Note that in both selects by USER3, USER3 does not have explicit privileges on the underlying types, but the statement succeeds because the type and table owners have the necessary privileges with the GRANT option.

Oracle checks privileges on the following requests, and returns an error if the requestor does not have the privilege for the action:

• Pinning an object in the object cache using its REF value causes Oracle to check SELECT privilege on the object table containing the object and EXECUTE privilege on the object type. (For more information about the OCI object cache, see "LNOCI Tips and Techniques for Objects".)
• Modifying an existing object or flushing an object from the object cache, causes Oracle to check UPDATE privilege on the destination object table. Flushing a new object causes Oracle to check INSERT privilege on the destination object table.
• Deleting an object causes Oracle to check DELETE privilege on the destination table.
• Invoking a method causes Oracle to check EXECUTE privilege on the corresponding object type.

Oracle does not provide column level privileges for object tables.

Dependencies and Incomplete Types

Types can depend upon each other for their definitions. For example, you might want to define object types employee and department in such a way that one attribute of employee is the department the employee belongs to and one attribute of department is the employee who manages the department.

Types that depend on each other in this way, either directly or through intermediate types, are called mutually dependent. In a diagram that uses arrows to show the dependency relationships among a set of types, connections among mutually dependent types form a loop.

To define such a circular dependency, you must use REFs for at least one segment of the circle.

For example, you can define the following types:

CREATE TYPE department;

CREATE TYPE employee AS OBJECT (
  name    VARCHAR2(30),
  dept    REF department,
  supv    REF employee );

CREATE TYPE emp_list AS TABLE OF employee;

CREATE TYPE department AS OBJECT (
  name    VARCHAR2(30),
  mgr     REF employee,
  staff   emp_list );

This is a legal set of mutually dependent types and a legal sequence of SQL DDL statements. Oracle compiles it without errors.

Notice that the preceding code creates the type department twice. The first statement:

CREATE TYPE department;

is an optional, incomplete declaration of department that serves as a placeholder for the REF attribute of employee to point to. The declaration is incomplete in that it omits the AS OBJECT phrase and lists no attributes or methods. These are specified later in the full declaration that completes the type. In the meantime, department is created as an incomplete object type. This enables the compilation of employee to proceed without errors.

To complete an incomplete type, you execute a CREATE TYPE statement that specifies the attributes and methods of the type, as shown at the end of the example. Complete an incomplete type after all the types that it refers to are created.

If you do not create incomplete types as placeholders, types that refer to the missing types still compile, but the compilation proceeds with errors.

For example, if department did not exist at all, Oracle would create it as an incomplete type and compile employee with errors. Then employee would be recompiled the next time that some operation attempts to access it. This time, if all the types it depends on are created and its dependencies are satisfied, it will compile without errors.

Incomplete types also enable you to create types that contain REF attributes to a subtype that has not yet been created. To create such a supertype, first create an incomplete type of the subtype to be referenced. Create the complete subtype after you create the supertype.

A subtype is just a specialized version of its direct supertype and consequently has an explicit dependency on it. To ensure that subtypes are not left behind after a supertype is dropped, all subtypes must be dropped first: a supertype cannot be dropped until all its subtypes are dropped.

Completing Incomplete Types

When all the types that an incomplete type refers to have been created, there is no longer any need for the incomplete type to remain incomplete, and you should complete the declaration of the type. Completing the type recompiles it and enables the system to release various locks.

You must complete an incomplete object type as an object type: you cannot complete an object type as a collection type (a nested table type or an array type). The only alternative to completing a type declaration is to drop the type.

You must also complete any incomplete types that Oracle creates for you because you did not explicitly create them yourself. The example in the preceding section explicitly creates department as an incomplete type. If department were not explicitly created as an incomplete type, Oracle would create it as one so that the employee type can compile (with errors). You must complete the declaration of department as an object type whether you or Oracle declared it as an incomplete type.

Manually Recompiling a Type

If a type was created with compilation errors, and you attempt some operation on it, such as creating tables or inserting rows, you may receive an error, Recompile type <typename> before attempting this operation. To manually recompile a type, execute an ALTER TYPE typename RECOMPILE statement. After you have successfully compiled the type, attempt the operation again.

Type Dependencies of Substitutable Tables and Columns

A substitutable table or column of type T is dependent not only on T but on all subtypes of T as well. This is because a hidden column is added to the table for each attribute added in a subtype of T. The hidden columns are added even if the substitutable table or column contains no data of that subtype.

So, for example, a persons table of type Person_typ is dependent not only on Person_typ but also on the Person_typ subtypes Student_typ and PartTimeStudent_typ.

If you attempt to drop a subtype that has a dependent type, table, or column, the DROP TYPE statement returns an error and aborts. For example, trying to drop PartTimeStudent_typ will raise an error because of the dependent persons table.

If dependent tables or columns exist but contain no data of the type that you want to drop, you can use the VALIDATE keyword to drop the type. The VALIDATE keyword causes Oracle to check for actual stored instances of the specified type and to drop the type if none are found. Hidden columns associated with attributes unique to the type are removed as well.

For example, the first DROP TYPE statement in the following example fails because PartTimeStudent_typ has a dependent table (persons). But if persons contains no instances of PartTimeStudent_typ (and no other dependent table or column does, either), the VALIDATE keyword causes the second DROP TYPE statement to succeed:

DROP TYPE PartTimeStudent_typ; -- Error due to presence of Persons table 
DROP TYPE PartTimeStudent_typ VALIDATE; -- Succeeds if there are no stored 
                                        -- instances of PartTimeStudent_typ

Note: Oracle recommends that you always use the VALIDATE option while dropping subtypes.

The FORCE Option

The DROP TYPE statement also has a FORCE option that causes the type to be dropped even though it may have dependent types or tables. The FORCE option should be used only with great care, as any dependent types or tables that do exist are marked invalid and become inaccessible when the type is dropped. Data in a table that is marked invalid because a type it depends on has been dropped can never be accessed again. The only action that can be performed on such a table is to drop it.

See Also: "Type Evolution" in Chapter 6 for information about how to alter a type

Synonyms for User-Defined Types

Just as you can create synonyms for tables, views, and various other schema objects, you can also define synonyms for user-defined types.

Synonyms for types have the same advantages as synonyms for other kinds of schema objects: they provide a location-independent way to reference the underlying schema object. An application that uses public type synonyms can be deployed without alteration in any schema of a database without having to qualify a type name with the name of the schema in which the type was defined.

See Also: Oracle9i Database Administrator's Guide for more information on synonyms in general

Creating a Type Synonym

You create a type synonym with a CREATE SYNONYM statement. The statement has the following syntax:

CREATE [OR REPLACE] [PUBLIC] SYNONYM [<schema>.]<name> FOR
[<schema>.]<type>[@<dblink>];

where <type> is a user-defined type.

For example, these statements create a type typ1 and then create a synonym for it:

CREATE TYPE typ1 AS OBJECT (x number);
CREATE SYNONYM syn1 FOR typ1;

Synonyms can be created for collection types, too. The following example creates a synonym for a nested table type:

CREATE TYPE typ2 AS TABLE OF NUMBER;
CREATE SYNONYM syn2 FOR typ2;

You create a public synonym by using the PUBLIC keyword:

CREATE TYPE shape AS OBJECT ( name VARCHAR2(10) );
CREATE PUBLIC SYNONYM pub_shape FOR shape;

The REPLACE option enables you to have the synonym point to a different underlying type. For example, the following statement causes syn1 to point to type typ2 instead of the type it formerly pointed to:

CREATE OR REPLACE SYNONYM syn1 FOR typ2;

Using a Type Synonym

You can use a type synonym anywhere that you can refer to a type. For instance, you can use a type synonym in a DDL statement to name the type of a table column or type attribute. In the following example, synonym syn1 is used to specify the type of an attribute in type typ3:

CREATE TYPE typ1 AS OBJECT (x number);
CREATE SYNONYM syn1 FOR typ1;
CREATE TYPE typ3 AS OBJECT ( a syn1 );

The next example shows a type synonym syn1 used to call the constructor of the user-defined type typ1, for which syn1 is a synonym. The statement returns an object instance of typ1:

SELECT syn1(0) FROM dual;

In the following example, syn2 is a synonym for a nested table type. The example shows the synonym used in place of the actual type name in a CAST expression:

SELECT CAST(MULTISET(SELECT sal FROM SCOTT.EMP) AS syn2) FROM dual;

Table 4-1 lists the kinds of statements in which type synonyms can be used.

Table 4-1

DML Statements	DDL Statements
SELECT	AUDIT
INSERT	NOAUDIT
UPDATE	GRANT
DELETE	REVOKE
EXPLAIN PLAN	COMMENT
LOCK TABLE

Describing Schema Objects That Use Synonyms

If a type or table has been created using type synonyms, the DESCRIBE command will show the synonyms in place of the types they represent. Similarly, catalog views (such as USER_TYPE_ATTRS) that show type names will show the associated type synonym names in their place.

You can query the catalog view USER_SYNONYMS to find out the underlying type of a type synonym.

Dependents of Type Synonyms

A type that directly or indirectly references a synonym in its type declaration is a dependent of that synonym. Thus, in the following example, type typ3 is a dependent type of synonym syn1.

CREATE TYPE typ3 AS OBJECT ( a syn1 );

Other kinds of schema objects that reference synonoyms in their DDL statements also become dependents of those synonyms. An object that depends on a type synonym depends on both the synonym and on the synonym's underlying type.

A synonym's dependency relationships affect your ability to drop or rename the synonym. Dependent schema objects are also affected by some operations on synonyms. The following sections describe these various ramifications.

Restriction on Replacing a Type Synonym

You can replace a synonym only if it has no dependent tables or valid user defined types.

Replacing a synonym is equivalent to dropping it and then re-creating a new synonym with the same name.

Dropping Type Synonyms

You drop a synonym with the DROP SYNONYM statement:

DROP SYNONYM pubsyn1;

You cannot drop a type synonym if it has table or valid user-defined types as dependents unless you use the FORCE option. The FORCE option causes any columns that directly or indirectly depend on the synonym to be marked unused, just as if the actual types of the columns were dropped. (A column indirectly depends on a synonym if, for instance, the synonym is used to specify the type of an attribute of the declared type of the column.)

Any dependent schema objects of a dropped synonym are invalidated. They can be revalidated by creating a local object of the same name as the dropped synonym or by creating a new public synonym with same name.

Dropping the underlying base type of a type synonym has the same effect on dependent objects as dropping the synonym.

Renaming Type Synonyms

You can rename a type synonym with the RENAME statement. The following example renames synonym employee:

RENAME employee TO emp;

Renaming a synonym is equivalent to dropping it and then re-creating it with a new name.

You cannot rename a type synonym if it has dependent tables or valid user-defined types.

Public Type Synonyms and Local Schema Objects

You cannot create a local schema object that has the same name as a public synonym if the public synonym has a dependent table or valid user-defined type in the local schema where you want to create the new schema object. Nor can you create a local schema object that has the same name as a private synonym in the same schema.

For instance, in the following example, table tab1 is a dependent table of public synonym pubsyn1 because the table has a column that uses the synonym in its type definition. Consequently, the attempt to create a table that has the same name as public synonym pubsyn1--in the same schema as the dependent table--will fail:

CREATE TABLE tab1 ( c1 pubsyn1 );    -- Uses public synonym pubsyn1
CREATE TABLE pubsyn1 ( c1 NUMBER );  -- Not allowed

Tools

This section describes several Oracle tools that provide support for Oracle objects.

JDeveloper

JDeveloper is a full-featured, integrated development environment for creating multitier Java applications. It enables you to develop, debug, and deploy Java client applications, dynamic HTML applications, web and application server components and database stored procedures based on industry-standard models.

JDeveloper provides powerful features in the following areas:

• Oracle Business Components for Java
• Web Application Development
• Java Client Application Development
• Java in the Database
• Component-Based Development with JavaBeans
• Simplified Database Access
• Visual Integrated Development Environment
• Java Language Support

JDeveloper runs on Windows NT. It provides a standard GUI based Java development environment that is well integrated with Oracle's Application Server and Database.

Business Components for Java (BC4J)

Supporting standard EJB and CORBA deployment architectures, Oracle Business Components for Java simplifies the development, delivery, and customization of Java business applications for the enterprise. Oracle Business Components for Java is an application component framework providing developers a set of reusable software building blocks that manage all the common facilities required to:

• Author and test business logic in components which integrate with relational databases
• Reuse business logic through multiple SQL-based views of data
• Access and update the views from servlets, JavaServer Pages (JSPs), and thin-Java Swing clients
• Customize application functionality in layers without requiring modification of the delivered application

JPublisher

JPublisher is a utility, written entirely in Java, that generates Java classes to represent the following user-defined database entities in your Java program:

• Database object types
• Database reference (REF) types
• Database collection types (varrays or nested tables)
• PL/SQL packages

JPublisher enables you to specify and customize the mapping of database object types, reference types, and collection types (varrays or nested tables) to Java classes, in a strongly typed paradigm.

See Also: Oracle9i JPublisher User's Guide

Utilities

Import/Export of Object Types

The Export and Import utilities move data into and out of Oracle databases. They also back up or archive data and aid migration to different releases of the Oracle RDBMS.

Export and Import support object types. Export writes object type definitions and all of the associated data to the dump file. Import then re-creates these items from the dump file.

Types

The definition statements for derived types are exported. On an Import, a subtype may be created before the supertype definition has been imported. In this case, the subtype will be created with compilation errors, which may be ignored. The type will be revalidated after its supertype is created.

Object View Hierarchies

View definitions for all views belonging to a view hierarchy are exported

SQL*Loader

The SQL*Loader utility moves data from external files into tables in an Oracle database. The files may contain data consisting of basic scalar datatypes, such as INTEGER, CHAR, or DATE, as well as complex user-defined datatypes such as row and column objects (including objects that have object, collection, or REF attributes), collections, and LOBs. Currently, SQL*Loader supports single-level collections only: you cannot yet use SQL*Loader to load multilevel collections, that is, collections whose elements are, or contain, other collections.

SQL*Loader uses control files, which contain SQL*Loader data definition language (DDL) statements, to describe the format, content, and location of the datafile(s).

SQL*Loader provides two approaches to loading data:

• Conventional path loading, which uses the SQL INSERT statement and a bind array buffer to load data into database tables
• Direct path loading, which uses the Direct Path Load API to write data blocks directly to the database on behalf of the SQL*Loader client.

  Direct path loading does not use a SQL interface and thus avoids the overhead of processing the associated SQL statements. Consequently, direct path loading tends to provide much better performance than conventional path loading.

Either approach can be used to load data of supported object and collection datatypes.

See Also: Oracle9i Database Utilities for instructions on how to use SQL*Loader