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UTL_REF

Oracle8i supports user-defined composite type or object type. Any instance of an object type is called an object. An object type can be used as the type of a column or as the type of a table.

In an object table, each row of the table stores an object. You can uniquely identify an object in an object table with an object identifier.

A reference is a persistent pointer to an object, and each reference can contain an object identifier. The reference can be an attribute of an object type, or it can be stored in a column of a table. Given a reference, an object can be retrieved.

The UTL_REF package provides PL/SQL procedures to support reference-based operations. Unlike SQL, UTL_REF procedures enable you to write generic type methods without knowing the object table name.

Requirements

The procedural option is needed to use this package. This package must be created under SYS (connect internal). Operations provided by this package are performed under the current calling user, not under the package owner SYS.

Datatypes

An object type is a composite datatype defined by the user or supplied as a library type. You can create the object type employee_type using the following syntax:

CREATE TYPE employee_type AS OBJECT (

name    VARCHAR2(20),
id      NUMBER,

member function GET_ID
    (name VARCHAR2) 
   RETURN MEMBER);

The object type employee_type is a user-defined type that contains two attributes, name and id, and a member function, GET_ID().

You can create an object table using the following SQL syntax:

CREATE TABLE employee_table OF employee_type;

Exceptions

Exceptions can be returned during execution of UTL_REF functions for various reasons. For example, the following scenarios would result in exceptions:

• The object selected does not exist. This could be because either:
  1. The object has been deleted, or the given reference is dangling (invalid).

  2. The object table was dropped or does not exist.

• The object cannot be modified or locked in a serializable transaction. The object was modified by another transaction after the serializable transaction started.

• You do not have the privilege to select or modify the object. The caller of the UTL_REF subprogram must have the proper privilege on the object that is being selected or modified.

  Table 64-1 UTL_REF Exceptions

  Exceptions	Description
  errnum == 942	Insufficient privileges.
  errnum == 1031	Insufficient privileges.
  errnum == 8177	Unable to serialize, if in a serializable transaction.
  errnum == 60	Deadlock detected.
  errnum == 1403	No data found (if the REF is null, etc.).

The UTL_REF package does not define any named exceptions. You may define exception handling blocks to catch specific exceptions and to handle them appropriately.

Security

You can use the UTL_REF package from stored PL/SQL procedures/packages on the server, as well as from client/side PL/SQL code.

When invoked from PL/SQL procedures/packages on the server, UTL_REF verifies that the invoker has the appropriate privileges to access the object pointed to by the REF.

Note: This is in contrast to PL/SQL packages/procedures on the server which operate with definer's privileges, where the package owner must have the appropriate privileges to perform the desired operations.

Thus, if UTL_REF is defined under user SYS, and user A invokes UTL_REF.SELECT to select an object from a reference, then user A (the invoker) requires the privileges to check.

When invoked from client-side PL/SQL code, UTL_REF operates with the privileges of the client session under which the PL/SQL execution is being done.