Value function (inheritance) in case clause

Question

I need to use the Value function to verify if it is an instance of the object in a clause marries. It is possible?
example:
-- structure:
-- create type object1 is object(field1 number);
-- create type object2 under object1(field2 number);
-- create type ot is table of object1;
-- objs ot;
select case when (value(t) is of (object1)) then 1
when (value(t) is of ((object2)) then 2
and case
from table (cast (objs as ot)) t
help me please. thanks

Answer 1

Try creating object1 with NOT FINAL. Also, if you are going to use the supertype first in your CASE expression, you need to use IS OF (ONLY object1). Else put the child types first...
SQL> create or replace type object1 is object(field1 number) not final;
Type created.
SQL> create type object2 under object1(field2 number);
Type created.
SQL> create or replace type ot is table of object1;
Type created.
SQL> select case
  2            when value(t) is of type (object1)
  3            then 1
  4            when value(t) is of type (object2)
  5            then 2
  6         end as supertype_goes_first
  7  from   table (cast(ot(object1(1),object2(1,2),object1(99),object2(2,100)) as ot)) t;
SUPERTYPE_GOES_FIRST
                   1
                   1
                   1
                   1
SQL>
SQL> select case
  2            when value(t) is of (only object1)
  3            then 1
  4            when value(t) is of type (object2)
  5            then 2
  6         end as is_of_only
  7  from   table (cast(ot(object1(1),object2(1,2),object1(99),object2(2,100)) as ot)) t;
IS_OF_ONLY
         1
         2
         1
         2
SQL>
SQL> select case
  2            when value(t) is of type (object2)
  3            then 1
  4            when value(t) is of type (object1)
  5            then 2
  6         end as subtype_before_supertype
  7  from   table (cast(ot(object1(1),object2(1,2),object1(99),object2(2,100)) as ot)) t;
SUBTYPE_BEFORE_SUPERTYPE
                       2
                       1
                       2
                       1