TREAT into an SQL request VS into pl/sql block

Question

Hello,
Something escape my understanding. The question is a little bit long for a probably short answer.
Thanks bothering reading it.
Claude
Situation:
CREATE OR REPLACE TYPE "A" AS OBJECT (v_a NUMBER) NOT FINAL;
CREATE OR REPLACE TYPE "B" UNDER A (v_b NUMBER)
ALTER TYPE B ADD MEMBER FUNCTION f_60 RETURN VARCHAR2 CASCADE;
CREATE OR REPLACE TYPE BODY "B" AS
MEMBER FUNCTION f_60 RETURN VARCHAR2 IS
BEGIN
RETURN 'FROM F_60';
END f_60;
END;
CREATE TABLE "TA" OF "A";
I INSERT successfully 3 instances of A and 2 instances of B INTO TA.
After I launch this working fine: SELECT TREAT( VALUE(p) AS B).f_60() FROM TA p;
Result-->
TREAT(VALUE(P)ASB).F_60()
FROM F_60
FROM F_60
<---
...But after that I try the following PL/SQL block:
DECLARE
TYPE list_A IS TABLE OF A;
v_list list_A;
BEGIN
SELECT VALUE(p) BULK COLLECT INTO v_list
FROM TA p; -- (ok if uncommented ->) WHERE VALUE(p) IS OF (B);
FOR r IN v_list.FIRST .. v_list.LAST LOOP
DBMS_OUTPUT.PUT_LINE(TREAT( v_list(r) AS B).f_60 );
END LOOP;
END;
Result: ORA-06502: PL/SQL: numeric or value error: cannot assign supertype instance to subtype
My question: in both cases the function f_60 is called in (it seems for me) the same condition. I mean in both cases the f_60 is called from a null object. Why the result differs then?
Thanks for any help on this.
Claude

Answer 1

You can do this by creating a string which is the full sql statement
and the executing it in PL/SQL.
For example, you have str1 := 'SDO_GEOMETRY(2006, 600000, NULL, SDO_ELEM_INFO_ARRAY(1, 2, 1, 13, 2, 1), SDO_ORDINATE_ARRAY(196741, 219623, 196743, 219623, 196745, 219623, 196746, 219637, 196742, 219639, 196741, 219623, 196746, 219637, 196746, 219637, 196746, 219637, 196746, 219637)) ';
Then make a SQL statement like this:
str2 := 'INSERT INTO new_linestrings (id,geom,orig_id) values ' || '('|| to_char(se_new_linestrings.nextval)|| ', ' ||str1|| ', ' ||to_char(orig_id) ') ';
execute immediate str2;
====
you may have to read in se_new_linestrings.nextval to a local variable
first.
siva