IS OF TYPE generates an exception - oracle

Question

I read about IS OF TYPE and I expected that it should return TRUE, FALSE or NULL.
I have two object types:
CREATE TYPE o1 AS OBJECT ( id NUMBER );
/
CREATE TYPE o2 AS OBJECT ( id NUMBER );
/
When I run the code below, everything is OK.
DECLARE
type1 o1;
BEGIN
type1 := o1(id=>1);
if (type1 IS OF (o1)) then
DBMS_OUTPUT.PUT_LINE('type1 is o1');
END if;
END;
/
But when I try to run:
DECLARE
type1 o1;
BEGIN
type1 := o1(id=>1);
if (type1 IS OF (o2)) then
DBMS_OUTPUT.PUT_LINE('type1 is o1');
END if;
END;
/
I received the following exceptions
Error report:
ORA-06550: line 6, column 21:
PLS-00382: expression is of wrong type
ORA-06550: line 6, column 4:
PL/SQL: Statement ignored
06550. 00000 - "line %s, column %s:\n%s"
*Cause: Usually a PL/SQL compilation error.
*Action:
In the documentation there isn't clear explanation, should I catch exception if something is of the wrong type? Or, should I expect false in the IF condition?

Answer 1

If you have declared your variable as O1 type then you can use is of [type] condition to test only whether your variable is of o1 type or is of o1's subtype. Here is an example(variables must be instantiated):
-- base type
SQL> create or replace type o1 as object(
2 prop number
3 )not final;
4 /
Type created
-- O1's subtype
SQL> create or replace type o2 under o1(
2 prop1 number
3 );
4 /
-- test if the l_o1 is of O1 type
SQL> declare
2 l_o1 o1;
3 begin
4 l_o1 := o1(prop=>1);
5 if l_o1 is of (o1)
6 then
7 dbms_output.put_line('Yes');
8 else
9 dbms_output.put_line('No');
10 end if;
11 end;
12 /
Yes
PL/SQL procedure successfully completed
-- test if the l_o1 is of O2 type
SQL> declare
2 l_o1 o1;
3 begin
4 l_o1 := o1(prop=>1);
5 if l_o1 is of (o2)
6 then
7 dbms_output.put_line('Yes');
8 else
9 dbms_output.put_line('No');
10 end if;
11 end;
12 /
No
PL/SQL procedure successfully completed
-- test if the l_o2 is of O2 type
SQL> declare
2 l_o2 o2;
3 begin
4 l_o2 := o2(prop=>1, prop1 => 1);
5 if l_o2 is of (o2)
6 then
7 dbms_output.put_line('Yes');
8 else
9 dbms_output.put_line('No');
10 end if;
11 end;
12 /
Yes
PL/SQL procedure successfully completed
Update:
Take a look at this to get more information about is of[type]. Usually data type of a variable is known at compile time, but if you have to deal with dynamic typing you may look at anydata(object data type). Here is a simple example:
SQL> declare
2 l_o1 o1;
3
4 -- Here is a procedure(for the sake of simplicity has not
5 -- been written as a schema object)
6 -- that doesn't not know
7 -- variable of what dada type will be passed in
8 -- at compile time;
9 procedure DoSomething(p_var anydata)
10 is
11 begin
12 case p_var.gettypename
13 when 'HR.O1'
14 then dbms_output.put_line('O1 data type. Do something');
15 when 'HR.O2'
16 then dbms_output.put_line('O2 data type. Do something');
17 else
18 dbms_output.put_line('Unknown data type');
19 end case;
20 end;
21
22 begin
23 l_o1 := o1(prop => 1);
24 DoSomething(anydata.ConvertObject(l_o1));
25 end;
26 /
O1 data type. Do something
PL/SQL procedure successfully completed