Monday, July 24, 2017

Document deprecated program units with new pragma (12.2)


Software is constantly evolving: bugs fixed, new features added, and better ways to do things discovered and implemented.

A great example of this dynamic from PL/SQL itself is the UTL_CALL_STACK package. This package was first introduced in Oracle Database 12c Release 1, and it improves upon the functionality already provided by the following functions in the DMBS_UTILITY package: FORMAT_CALL_STACK, FORMAT_ERROR_STACK, and FORMAT_ERROR_BACKTRACE.

The same thing happens in PL/SQL code that is developed by customers. The now-outdated subprograms (or other elements) of one's API cannot be removed immediately; that would break existing code. But everyone would like to make sure that any new code uses the new API.

The new DEPRECATE pragma (compiler directive) in Oracle Database 12.2 will help you accomplish this transition in a smooth, error-free fashion. It provides a formal way to communicate information about deprecated elements [my change ok? SF YES] with a power that ordinary external documentation cannot convey.

You can apply this new pragma to a whole unit, to a subprogram within a unit, at any level of nesting, to any definition, and so on. When a unit is compiled that makes a reference to a deprecated element, a warning is displayed (when you have compile time warnings enabled).

Let's take a look at some examples.

1. Deprecate an entire package.

CREATE PACKAGE pkg AUTHID DEFINER 
AS
   PRAGMA DEPRECATE(pkg);

   PROCEDURE proc;
   FUNCTION func RETURN NUMBER;
END;

2. Deprecate a subprogram in a package. Note the comment added to the pragma. This text will be displayed along with the warning/error information.

CREATE PACKAGE pkg AUTHID DEFINER
AS
  PROCEDURE proc;
  PRAGMA DEPRECATE (
    proc,
    ’pkg.proc deprecated. Use pkg.new_proc instead.’);

  PROCEDURE new_proc;
END;

Let's try using that deprecated procedure, with warnings enabled.

ALTER SESSION SET plsql_warnings = 'enable:all'
/

CREATE OR REPLACE PROCEDURE use_deprecated
   AUTHID DEFINER
IS
BEGIN
   pkg.proc;
END;
/

Procedure USE_DEPRECATED compiled with warnings

PLW-06020: reference to a deprecated entity: PROC declared in unit PKG[4,14]. pkg.proc deprecated. 
   Use pkg.new_proc instead.

Deprecation Warnings

PL/SQL in Oracle Database 12.2 has four new warnings to help you utilize the DEPRECATE pragma:

6019. The entity was deprecated and could be removed in a future release. Do not use the deprecated entity.

6020. The referenced entity was deprecated and could be removed in a future release. Do not use the deprecated entity. Follow the specific instructions in the warning if any are given.

6021. Misplaced pragma. The DEPRECATE pragma should follow immediately after the declaration of the entity that is being deprecated. Place the pragma immediately after the declaration of the entity that is being deprecated.

6022. This entity cannot be deprecated. Deprecation only applies to entities that may be declared in a package or type specification as well as to top-level procedure and function definitions. Remove the pragma.

Try it on LiveSQL!

I know, I know. You'd love to start exploring this and other new features in 12.2, but you don't yet have 12.2 installed at work. No problem!

LiveSQL offers free, 24x7 access to a 12.2 schema. You can execute SQL and PL/SQL code to your heart's content.

You can also run scripts that others, including myself, have uploaded to LiveSQL.

Here's one on the deprecate pragma. Enjoy!

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