|Oracle9i Application Developer's Guide - Object-Relational Features
Release 2 (9.2)
Part Number A96594-01
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 for object types exist at the system level and the schema object level.
Oracle defines the following system privileges for object types:
CREATE TYPEenables you to create object types in your own schema
CREATE ANY TYPEenables you to create object types in any schema
ALTER ANY TYPEenables you to alter object types in any schema
DROP ANY TYPEenables you to drop named types in any schema
EXECUTE ANY TYPEenables you to use and reference named types in any schema
UNDER ANY TYPEenables you to create subtypes under any non-final object types
UNDER ANY VIEWenables you to create subviews under any object view
RESOURCE roles include the
CREATE TYPE system privilege. The DBA role includes all of these privileges.
Two schema object privileges apply to object types:
EXECUTEon an object type enables you to use the type to:
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.
UNDERenables you to create a subtype/subview under the type/view on which the privilege is granted
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.
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.
In addition to the permissions detailed in the previous sections, you need specific privileges to:
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.
Assume that three users exist with the
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
TYPE2 with the
However, the following grant fails because
USER2 does not have
USER1.TYPE1 with the
USER3 can successfully perform the following actions:
While object types only make use of
EXECUTE privilege, object tables use all the same privileges as relational tables:
SELECTlets you access an object and its attributes from the table.
UPDATElets you modify attributes of objects in the table.
INSERTlets you add new objects to the table.
DELETElets 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:
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
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:
Note that in both selects by
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
Oracle checks privileges on the following requests, and returns an error if the requestor does not have the privilege for the action:
SELECTprivilege on the object table containing the object and
EXECUTEprivilege on the object type. (For more information about the OCI object cache, see "LNOCI Tips and Techniques for Objects".)
UPDATEprivilege on the destination object table. Flushing a new object causes Oracle to check
INSERTprivilege on the destination object table.
DELETEprivilege on the destination table.
EXECUTEprivilege on the corresponding object type.
Oracle does not provide column level privileges for object tables.
Types can depend upon each other for their definitions. For example, you might want to define object types
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:
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.
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.
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.
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
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
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
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.
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.
Oracle9i Database Administrator's Guide for more information on synonyms in general
You create a type synonym with a
CREATE SYNONYM statement. The statement has the following syntax:
<type> is a user-defined type.
For example, these statements create a type
typ1 and then create a synonym for it:
Synonyms can be created for collection types, too. The following example creates a synonym for a nested table type:
You create a public synonym by using 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:
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
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
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
Table 4-1 lists the kinds of statements in which type synonyms can be used.
|DML Statements||DDL Statements|
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.
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
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.
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.
You drop a synonym with the
DROP SYNONYM statement:
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.
You can rename a type synonym with the
RENAME statement. The following example renames synonym
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.
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
This section describes several Oracle tools that provide support for Oracle objects.
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:
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.
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:
JPublisher is a utility, written entirely in Java, that generates Java classes to represent the following user-defined database entities in your Java program:
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.
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.
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.
View definitions for all views belonging to a view hierarchy are exported
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
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:
SQL INSERTstatement and a bind array buffer to load data into database tables
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.
Oracle9i Database Utilities for instructions on how to use SQL*Loader