create trigger to save CONSTRAINTs changes on tables in oracle - oracle

Question

I want to create table to save all CONSTRAINTs changes in my oracle database,
so i have created this table(table name , constraint name , date , mode like [insert|update|delete] )
CREATE TABLE CONS
(
C_ID NUMBER NOT NULL
, C_NAME VARCHAR2(50) NOT NULL
, T_NAME VARCHAR2(50) NOT NULL
, EXE_DATE DATE NOT NULL
, MODE VARCHAR2(50) NOT NULL
);
the problem was by insert data,
I was thinking of creating trigger on user_cons_columns after insert or update or delete,
but I found that user_cons_columns is a view and i can't create trigger on it,
so how can I do this work?
or what is the tables that I can create trigger on it to do this???
thanks .......

Answer 1

User_Cons_Columns is metadata view in oracle and you can not use it for monitoring constraint changes.
I think, You can use this metadata view :
SELECT *
FROM ALL_CONSTRAINTS T
It shows which constraint has changed by LAST_CHANGE Column and other data that you can use them.

Answer 2

I don't know if we can create DML TRIGGERs on data dictionary tables in Oracle, but that sounds like a bad idea.
My suggestion to you would be to create a DDL Trigger on the ALTER event
Firstly, as a one time activity, you could store all the available constraints in your CONS table.
Then in your trigger, you could use these conditions to check if a table and column was altered.
if (ora_sysevent = 'ALTER' and
ora_dict_obj_type = 'TABLE')
then alter_column :=
ora_is_alter_column('FOO');
end if;
You could then query the user_cons_columns , ALL_CONSTRAINTS and CONS - whichever you find is relevant to store your data - to find if a new constraint was added or not. If it was indeed added or modified, make an entry into CONS or else update it ( using MERGE statement )

Answer 3

As you said, you can't create that type of a trigger on USER_CONS_COLUMNS:
SQL> create or replace trigger trg_myucc
2 before insert
3 on user_cons_columns
4 begin
5 null;
6 end;
7 /
create or replace trigger trg_myucc
*
ERROR at line 1:
ORA-25001: cannot create this trigger type on this type of view
Why wouldn't we try INSTEAD OF TRIGGER?
SQL> create or replace trigger trg_myucc
2 instead of insert
3 on user_cons_columns
4 for each row
5 begin
6 null;
7 end;
8 /
on user_cons_columns
*
ERROR at line 3:
ORA-01031: insufficient privileges
OK, that won't work either. But, what prevents us on creating a view upon a view, and then create INSTEAD OF trigger on that newly created view?
SQL> create or replace view my_ucc as select * from user_cons_columns;
View created.
SQL> create or replace trigger trg_myucc
2 instead of insert
3 on my_ucc
4 for each row
5 begin
6 null;
7 end;
8 /
Trigger created.
Fine; now you have a way to do what you're supposed to do. More about triggers here.