ORA-22979: cannot INSERT object view REF or user-defined REF

Question

I'm getting this error when trying to insert a parent_type object into an object table. The parent object contains a nested table of parent object references.
CREATE TYPE cl_ArgList AS TABLE OF REF cl_Expression
CREATE TYPE cl_Expression AS OBJECT (
args cl_ArgList;
Somehow the system-generated parent object REF that is returned from one STATIC function (using MAKE_REF) turns into a incompatible REF by the time it is passed to aother STATIC function and used in the constructor of the nested table for a new args instance.
Does anybody know how this might be happening?
Is there any way to test if a REF is a valid system-generated REF vs. a user-defined REF?
I don't even know what a user-defined REF is, how I might be getting one, and what's wrong with it anyway. Shouldn't strong-typing ensure that the REF is okay if it is of the appropriate type?
Glenn.

Answer 1

Okay, solved that.
FYI the problem is that the nested table arguments (REF cl_Expression) have to be SCOPED REFs, ie. constrained to refer only to objects in a particular table (although I don't really understand why).
Then of course the trick is how to constrain the arguments in the nested table, because you can't do it in the CREATE TYPE statement. You also can't do it when you create the containing table, when you define how the nested table is stored:
CREATE TABLE <containing table> OF cl_Expression (
NESTED TABLE args STORE AS t_args
Instead you have to modify the nested table properties after it has been created:
ALTER TABLE t_args ADD (SCOPE FOR (column_value) IS t_Induhvidual);
'column_value' is the actual syntax, not your own column name.
But you probably knew that ;-)