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

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 the above 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 "OCI 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. A diagram of mutually dependent types, with arrows representing the dependencies, always reveals a path of arrows starting and ending at one of the types.

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. The first statement:

CREATE TYPE department;

is optional. It makes the compilation proceed without errors. It establishes department as an incomplete object type. A REF to an incomplete object type compiles without error, so the compilation of employee proceeds.

When Oracle reaches the statement that completes the definition of department, all of the components of department have compiled successfully, so the compilation finishes without errors.

Without the optional declaration of department as an incomplete type, employee compiles with errors. Oracle then automatically adds employee to its library of schema objects as an incomplete object type. This makes the declarations of emp_list and department compile without errors. When employee is recompiled after emp_list and department are complete, employee compiles without errors and becomes a complete object type.

Incomplete types also enable you to create types that contain REF attributes to a subtype, which 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 avoid leaving behind subtypes that lack a supertype, a supertype cannot be dropped unless all its subtypes are dropped first.

Completing Incomplete Types

Once you have declared an incomplete object type, you must complete it as an object type. You cannot, for example, declare it to be a table type or an array type. The only alternative is to drop the type.

This is also true if Oracle has made the type an incomplete object type for you--as it did when EMPLOYEE failed to compile in the previous section.

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 below will fail 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 will cause 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

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 multi-level 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.