User-defined constructor in SQL

Question

Below is a SQL*Plus script to create an object type and a collection
type, followed by an anonymous block. The anonymous block attempts to
create 3 instances of the object type.
1. With the default constructor in a SELECT.. INTO.. - it succeeds.
2. With a user-defined constructor in an assignment statement - it succeeds.
3. With a user-defined constructor in a SELECT.. INTO.. - it fails.
Why does the third attempt fail?
The server is Oracle9i Enterprise Edition Release 9.2.0.1.0 and the
results are the same on Linux and Solaris.
My attempts to search this forum resulted in "The page caused an ESI
processing exception.", my apologies if my question has already been
discussed.
Thanks
----------------------------- Sample code -------------------------------------
CREATE OR REPLACE TYPE t_thing AS OBJECT
( n INTEGER,
x VARCHAR2(20),
CONSTRUCTOR FUNCTION t_thing (i_n IN INTEGER) RETURN SELF AS RESULT
CREATE OR REPLACE TYPE BODY t_thing AS
CONSTRUCTOR FUNCTION t_thing (i_n IN INTEGER) RETURN SELF AS RESULT IS
BEGIN
SELF.n := i_n;
SELF.x := 'some default';
DBMS_OUTPUT.PUT_LINE('Constructor built thing ' || SELF.n);
RETURN;
END t_thing;
END;
CREATE TYPE t_things IS TABLE OF t_thing NOT NULL;
DECLARE
v_things t_things;
v_one_thing t_thing;
BEGIN
-- 1.
SELECT NEW t_thing(1, 'a') BULK COLLECT INTO v_things FROM dual;
FOR i IN v_things.FIRST..v_things.LAST
LOOP
DBMS_OUTPUT.PUT_LINE
( 'This thing has n `' || v_things(i).n || ''''
|| ' and x `' || v_things(i).x || '''.'
END LOOP;
-- 2.
v_one_thing := NEW t_thing(2);
-- 3.
SELECT NEW t_thing(3) BULK COLLECT INTO v_things FROM dual;
END;
------------------------ The output from the sample code ----------------------
SQL> @test
Type created.
Type body created.
Type created.
This thing has n `1' and x `a'.
Constructor built thing 2
DECLARE
ERROR at line 1:
ORA-06552: PL/SQL: Statement ignored
ORA-06553: PLS-302: component 'T_THING' must be declared
ORA-06512: at line 21

Answer 1

William,
You can use the default constructor in 9i release. In addition, a static method can be used as user-defined constructors. Please check out the documentation at http://otn.oracle.com/docs/products/oracle9i/doc_library/901_doc/appdev.901/a88878/adobjdes.htm#444053
Regards,
Geoff
Hi, I am currently working in O/R model in a 9i DB. I have a type hierarchy in which there are a super-type (not instantiable) and some sub-types that add new attributes. I want to create an instance(object) of an specific sub-type using the specific constructor for this sub-type(with his own parameters list, in this case the parameters that correspond to the new attributes added), inside this constructor I will set the values to the attributes that the sub-type inherited from his parent and the values passed to the new added attributes.
Is it possible programming in PL/SQL?