Monday, July 11, 2005

The IN Thing: The example

OK, so how do we actually implement the Table cast lookup with a ref cursor?

First, we bear in mind that this is the most complex TABLE cast we can perform, since we need the data and definition to be available outside of the function that is performing the table cast.

The example given has a very simple main cursor, which is effectively:

SELECT *
FROM product


This makes the method appear a little overtly complex. In reality, the main cursor would have to be a lot more complex in order to merit this approach. Additionally, it is most useful when the results are pulled into a higher tier that is not Oracle bound. E.G. An object oriented tier in Java / PHP or the like, where you want to ensure that the record you get back is always in the same form, so you can construct a complete object.

The Example:

Please forgive the scrolling window...



In order to have something to access, we need the tables and data:


CREATE TABLE product
( id NUMBER
, descr VARCHAR2( 100 ) )
/

INSERT INTO product ( id, descr ) VALUES ( 1, 'one' );
INSERT INTO product ( id, descr ) VALUES ( 2, 'two' );
INSERT INTO product ( id, descr ) VALUES ( 3, 'three' );
INSERT INTO product ( id, descr ) VALUES ( 4, 'four' );
INSERT INTO product ( id, descr ) VALUES ( 5, 'five' );
INSERT INTO product ( id, descr ) VALUES ( 6, 'six' );

COMMIT;



In order to perform the cast we need to declare a type for the row in the table, and then the table type itself:


CREATE TYPE gt_id_type AS OBJECT ( id NUMBER )
/

CREATE TYPE gt_id_list_type AS TABLE OF gt_id_type
/


Then we define the package that will perform the cast.
We have the following functions

  • GET_PRODUCTS, which is passed a table of IDs, and returns a ref cursor containing the products requested.

  • GET_PRODS_BY_NAME, which is passed a string, and returns all the products that have a description containing that string. This function uses GET_PRODUCTS to return the product details

  • GET_ID_LIST, which is a helper function used by GET_PRODUCTS in order to make the list of product IDs available to the outside world (so the ref cursor doesn't fail when it's fetched from).



CREATE OR REPLACE PACKAGE product_pkg AS
TYPE gt_product_cur IS REF CURSOR;
FUNCTION get_products ( pt_id_list gt_id_list_type )
RETURN gt_product_cur;
FUNCTION get_prods_by_name ( pc_product_name VARCHAR2 )
RETURN gt_product_cur;
FUNCTION get_id_list RETURN gt_id_list_type;
END;
/

CREATE OR REPLACE PACKAGE BODY product_pkg AS
--
gt_id_list gt_id_list_type;
--
FUNCTION get_id_list RETURN gt_id_list_type IS
BEGIN
RETURN gt_id_list;
END;
--
FUNCTION get_products
( pt_id_list gt_id_list_type )
RETURN gt_product_cur IS
--
vt_product_cur gt_product_cur;
--
BEGIN
--
gt_id_list := pt_id_list;
--
OPEN vt_product_cur FOR
SELECT *
FROM product
WHERE id IN ( SELECT id
FROM TABLE( product_pkg.get_id_list()));
--
RETURN vt_product_cur;
--
END;
--
FUNCTION get_prods_by_name
( pc_product_name VARCHAR2 )
RETURN gt_product_cur IS
--
vt_product_ids gt_id_list_type;
--
BEGIN
--
SELECT gt_id_type( id )
BULK COLLECT
INTO vt_product_ids
FROM product
WHERE descr LIKE '%'|| pc_product_name|| '%';
--
RETURN get_products( vt_product_ids );
--
END;
--
END;
/



Finally, we have some code to run the GET_PRODS_BY_NAME function and return its set of values.


SET SERVEROUTPUT ON SIZE 1000000

DECLARE
--
vt_cur product_pkg.gt_product_cur;
vr_product_rec product%ROWTYPE;
--
BEGIN
--
vt_cur := product_pkg.get_prods_by_name( 't' );
--
LOOP
--
FETCH vt_cur INTO vr_product_rec;
EXIT WHEN vt_cur%NOTFOUND;
DBMS_OUTPUT.PUT_LINE( vr_product_rec.descr );
--
END LOOP;
--
END;
/


And the output:


two
three


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