Constants in object-CodePudding

I have an object type like below:

CREATE OR REPLACE TYPE MYOBJ AS OBJECT( Att VARCHAR2(200) );

I wish to have some constants attributes there. How should I program it? I mean I wish to have something like:

Att CONSTANT VARCHAR2(200) := 'Something'

Can I do it in spec? Or in constructor? Is it possible at all?

CodePudding user response：

You cannot have a CONSTANT attribute of an object.

There are two alternate methods you can take:

initialise a non-constant value in the constructor (and never change it); or
create a static function:

CREATE OR REPLACE TYPE MYOBJ AS OBJECT(
  Att VARCHAR2(200),
  
  CONSTRUCTOR FUNCTION myobj RETURN SELF AS RESULT,
  STATIC FUNCTION const_value RETURN VARCHAR2
);

CREATE OR REPLACE TYPE BODY MYOBJ AS
  CONSTRUCTOR FUNCTION myobj RETURN SELF AS RESULT
  IS
  BEGIN
    SELF.att := 'ABC';
    RETURN;
  END;

  STATIC FUNCTION const_value RETURN VARCHAR2
  IS
  BEGIN
    RETURN 'ABC';
  END;
END;
/

Then:

SELECT MYOBJ().ATT FROM DUAL;

Creates an instance of the object, initialises the att attribute in the constructor and then returns it. However, the value is not a constant so it is possible to modify it (but if you never change it then it will be effectively constant).

Or you can call the static function:

SELECT MYOBJ.const_value() FROM DUAL;

Which will be constant but it is not an attribute of the object.

db<>fiddle here