Adding a constraint to an attributes of an existing object

Question

Hi ,
I need to to add a CHECK constraint into a user defined object. This object exists already and used in a table , I cannot find the correct syntax to add the CHECK constraint to one of the attributes of the object.
I have added the following, a NOT NULL constraint to it without any errors.
ALTER TYPE USER_OBJ
MODIFY ATTRIBUTE (ATTRB_A VARCHAR2(30) NOT NULL)
CASCADE;
But when I try and do the same with a CHECK (IN ) constraint I keep getting errors stating wrong syntax or expecting an operator.
I have searched and just cannot find if what I am attempting is possible or not in Oracle 9i - Is it and if it is how does one do it ?
Thanks for any assistance in this
Regards
Eoin

Answer 1

If you read the documentation you will see that Oracle does not support constraints and defaults in type specifications. I think the fact that the ALTER TYPE statement works is a bug.
Consider what happens when we try to create a type with a NOT NULL attribute...
SQL> CREATE TYPE  user_obj AS OBJECT (attrb_a VARCHAR2(30) NOT NULL)
  2  /
Warning: Type created with compilation errors.
SQL> show error
Errors for TYPE USER_OBJ:
LINE/COL ERROR
1/27     PLS-00218: a variable declared NOT NULL must have an
         initialization assignmentHmmm, can't do that. So let's go down the ALTER route...
SQL> CREATE OR REPLACE TYPE  user_obj AS OBJECT (attrb_a VARCHAR2(30) )
  2  /
Type created.
SQL> ALTER  TYPE user_obj
  2     MODIFY ATTRIBUTE (ATTRB_A  NOT NULL)
  3  /
ALTER  TYPE user_obj
ERROR at line 1:
ORA-06545: PL/SQL: compilation error - compilation aborted
ORA-06550: line 3, column 31:
PLS-00103: Encountered the symbol "NOT" when expecting one of the following:
<an identifier> <a double-quoted delimited-identifier> LONG_
double ref char time timestamp interval date binary national
character nchar
The symbol "<an identifier>" was substituted for "NOT" to continue.
ORA-06550: line 0, column 0:
PLS-00565: USER_OBJ must be completed as a potential REF target (object type)
SQL>  ALTER  TYPE user_obj
  2      MODIFY ATTRIBUTE (ATTRB_A  VARCHAR2(30)  NOT NULL)
  3  /
ALTER  TYPE user_obj
ERROR at line 1:
ORA-22324: altered type has compilation errors
ORA-22328: object "APC"."USER_OBJ" has errors.
PLS-00719: only widening of attribute 'ATTRB_A' constraints is allowed
ORA-06550: line 0, column 0:
PL/SQL: Compilation unit analysis terminated
SQL>  ALTER  TYPE user_obj     MODIFY ATTRIBUTE (ATTRB_A  VARCHAR2(31)  NOT NULL)
  2  /
Type altered.Anything with so wacky a syntax just cannot be correct. Was the effort worth while?
SQL> declare
  2   u user_obj;
  3  begin
  4   u := USER_OBJ('APC');
  5  end;
  6  /
PL/SQL procedure successfully completed.
SQL> declare
  2   u user_obj;
  3  begin
  4   u := USER_OBJ(NULL);
  5  end;
  6  /
PL/SQL procedure successfully completed.
SQL> desc user_obj
Name                                      Null?    Type
ATTRB_A                                            VARCHAR2(31)
SQL> That'll be a "No" then.
Cheers, APC