Master/Details tables with CASCADE delete giving "table mutating" error

Question

Hi,
I have two tables in a master/details configuration (table 1 is "master", table 2 is "details").
The details has a FK contraint relation to the master with a CASCADE delete (so when the master is deleted, all associated details are deleted).
The master table has a column "last_updated_datetime" which is updated by a master table update trigger whenever most (excluding the last_updated_datetime column) columns are updated.
The details table has an update trigger which also updates the master table's last_updated_datetime column (whenever a detail row is changed).
The details table also has a delete trigger which also updated the master table's last_updated_datetime column (whenever a detail row is deleted).
The problem I have is: When the master record is deleted, which cascade deletes the details record(s), the delete trigger on the details table throws a "table is mutating" error.
I understand that the "mutating" error is "correct" because the master record is being deleted.
But is there some way I can get around this problem (for example, having the details table delete trigger not update the master table last_updated_datetime) when it's this cascade delete?
Thanks for your help!

Answer 1

create table master (
  id number primary key,
  changed date not null
create table detail (
  id number primary key,
  master_id references master (id) on delete cascade
create or replace package pkg is
  master_deleted boolean := false;
end;
create or replace trigger bds_master
  before delete on master
begin
  pkg.master_deleted := true;
end;
create or replace trigger ads_master
  after delete on master
begin
  pkg.master_deleted := false;
end;
create or replace trigger adr_detail
  after delete on detail
  for each row
begin
if not pkg.master_deleted then
    update master
       set changed = sysdate
     where id = :old.master_id;
  end if;
end;
insert into master values (1, sysdate - 10);
insert into detail values (11, 1);
insert into detail values (12, 1);
insert into master values (2, sysdate - 10);
insert into detail values (21, 2);
insert into detail values (22, 2);
insert into master values (3, sysdate - 10);
insert into detail values (31, 3);
insert into detail values (32, 3);
commit;
select * from master order by id;
        ID CHANGED                                                             
         1 01.09.08                                                            
         2 01.09.08                                                            
         3 01.09.08                                                            
select * from detail order by id;
        ID  MASTER_ID                                                          
        11          1                                                          
        12          1                                                          
        21          2                                                          
        22          2                                                          
        31          3                                                          
        32          3                                                          
delete detail where id = 21;
select * from master order by id;
        ID CHANGED                                                             
         1 01.09.08                                                            
         2 11.09.08
         3 01.09.08                                                            
select * from detail order by id;
        ID  MASTER_ID                                                          
        11          1                                                          
        12          1                                                          
        22          2                                                          
        31          3                                                          
        32          3                                                          
delete master where id in (1, 2);
select * from master order by id;
        ID CHANGED                                                             
         3 01.09.08                                                            
select * from detail order by id;
        ID  MASTER_ID                                                          
        31          3                                                          
        32          3                                                           Regards,
Zlatko
Edited by: Zlatko Sirotic on Sep 11, 2008 11:15 PM
This is disaster - ten attempts to format code!