Pass PL/SQL collection as function parameter over DBLink

Question

Hi all,
I am trying to do the following;
---Remote database
--create SQL type
create type attributeidarray as table of varchar2(255);
--create a package specs
CREATE OR REPLACE PACKAGE testp
AS
TYPE ref_res IS REF CURSOR;
FUNCTION foo (i NUMBER)
RETURN NUMBER;
FUNCTION foo1 (i NUMBER, j attributeidarray)
RETURN NUMBER;
END;
--create package body
CREATE OR REPLACE PACKAGE BODY testp
IS
--Function does nothing other than return number
FUNCTION foo (i NUMBER)
RETURN NUMBER
IS
res ref_res;
a array_n;
BEGIN
OPEN res
FOR
SELECT *
FROM DUAL;
RETURN 1;
END;
--Function takes the collection as imput and does nothing with it. Function just returns number
FUNCTION foo1 (i NUMBER, j attributeidarray)
RETURN NUMBER
IS
res ref_res;
a array_n;
BEGIN
OPEN res
FOR
SELECT *
FROM DUAL;
RETURN 1;
END;
END;
--"Near" Database ..
--create a SQL type
--This is the exactly the same as in remote database
create type attributeidarray as table of varchar2(255);
--create a DBLink
create database link con_to_remote_db
connect to remotedbuser
identified by "swordfish"
using 'remotedb'
--call the remote functions and pass a collection object
SQL> DECLARE
2 a attributeidarray;
3 BEGIN
4 SELECT CAST (attributeidarray (1, 2) AS attributeidarray)
5 INTO a
6 FROM DUAL;
7
8 :b := testp.foo@con_to_remote_db (2);
9 END;
10 /
PL/SQL procedure successfully completed.
SQL> print b
B
1
SQL>
--so far so good...
SQL> DECLARE
2 a attributeidarray;
3 BEGIN
4 SELECT CAST (attributeidarray (1, 2) AS attributeidarray)
5 INTO a
6 FROM DUAL;
7
8 :b := testp.foo1@con_to_remote_db (2, a);
9 END;
10 /
:b := testp.foo1@con_to_remote_db (2, a);
ERROR at line 8:
ORA-06550: line 8, column 10:
PLS-00306: wrong number or types of arguments in call to 'FOO1'
ORA-06550: line 8, column 4:
PL/SQL: Statement ignored
--Oops...doesn't seem to recognize the collection type :( /b]
So I wish to know the following;
- Even though the definition for type is the same, why is the remote DB not recognizing my type?
- It would be helpful if any one can let me know the correct method to pass a collection type with a example.
I would appreciate any help in resolving this issue.
Thanks,
prashant

Answer 1

Not possible. For valid technical reasons.
Definitions are local to a database. You can define a SQL user type called TMyType in your database. I can define one in mine with the same name.
Can you now call my database, passing a collection of your TMyType to me? How do we (or Oracle) know that your definition and my definition is the same? Or if they were the same when you compiled your code (and your Oracle checked my Oracle to confirm), that they still are the same and that I did not in the meantime altered the type? Or even dropped it?
For types/collections to be transparently passed across to database links, we need something along the lines of:
a) global types
b) runtime checking of types
Both are problematic to implement and maintain. With (a) there is the issue of dependencies. The global type cannot be changed before all dependencies on all subscribers have been resolved. With (b) there is the issue of performance, checking the type definitions with every single call on the local & remote instances to compare.
It would be a nice feature to have... but it would fail to live up to expectation if not implemented in a robust and performant way.
Alternative. "Insert" data via a remote proc into a remote collection. This allows you to push data into a PGA memory structure on the remote side and when done, allows you to tell that remote proc to "flush" (forall insert/update/delete) the contents of that structure to disk.