Passing objects by reference in PL/SQL

Question

Hi,
I have come across an unexpected problem using object types in PL/SQL that is causing me some grief. I'm from a Java background and am relatively new to Oracle Objects but what I'm trying to do is fairly trivial, I think. The code below illustrates the problem.
--- cut here ---
CREATE OR REPLACE TYPE test_obj_t AS OBJECT
num INTEGER,
CONSTRUCTOR FUNCTION test_obj_t RETURN SELF AS RESULT
CREATE OR REPLACE TYPE BODY test_obj_t IS
CONSTRUCTOR FUNCTION test_obj_t RETURN SELF AS RESULT IS
BEGIN
num := 0;
RETURN;
END;
END;
CREATE OR REPLACE PACKAGE test_obj_ref AS
PROCEDURE init(o IN test_obj_t);
PROCEDURE inc;
FUNCTION get_num RETURN INTEGER;
END;
CREATE OR REPLACE PACKAGE BODY test_obj_ref IS
obj test_obj_t;
PROCEDURE init(o IN test_obj_t) IS
BEGIN
obj := o;
END;
PROCEDURE inc IS
BEGIN
obj.num := obj.num + 1;
END;
FUNCTION get_num RETURN INTEGER IS
BEGIN
RETURN obj.num;
END;
END;
--- cut here ---
The object type test_obj_t holds a integer and the test_obj_ref package holds a 'reference' to an instance of the object.
To test the above code I run this PL/SQL block:
declare
obj test_obj_t;
begin
obj := test_obj_t;
test_obj_ref.init(obj);
dbms_output.put_line('obj.num='||obj.num);
dbms_output.put_line('test_obj_ref.get_num='||test_obj_ref.get_num);
test_obj_ref.inc;
dbms_output.put_line('obj.num='||obj.num);
dbms_output.put_line('test_obj_ref.get_num='||test_obj_ref.get_num);
test_obj_ref.inc;
dbms_output.put_line('obj.num='||obj.num);
dbms_output.put_line('test_obj_ref.get_num='||test_obj_ref.get_num);
end;
giving the output:
obj.num=0
test_obj_ref.get_num=0
obj.num=0
test_obj_ref.get_num=1
obj.num=0
test_obj_ref.get_num=2
It appears that the object held by the test_obj_ref package is being incremented as expected, but I would have expected the object declared in the PL/SQL block to be pointing to the same object and so should report the same incremented values.
I suspect that the object is copied in the call to test_obj_ref.init() so I end up with two object instances, one that is held by the test_obj_ref package and one in the anonymous block. Although, I thought that all IN parameters in PL/SQL are passed by reference and not copied!
Am I right?
Is passing objects by reference possible in PL/SQL, if so how?
I'm using Oracle 10.2.0.3.
Cheers,
Andy.

Answer 1

the object being passed to the test_obj_ref.init+ procedure is passed by reference; however, when you assign it to your package variable obj it is being copied to a new instance. you can pass object instances as parameters to procedures using the +IN OUT [NOCOPY]+ *calling mode, in which case modifications to the attributes of the passed object will be reflected in the calling scope's instance variable.
oracle's only other notion of an object reference is the +"REF <object-type>"+ datatype, which holds a reference to an object instance stored in an object table or constructed by an object view.
hope this helps...
gerard