Stoyan Genov wrote:
> ...
> I would like also to build a rule which works on the "reverse DELETE"
> condition, and disallows deleting t1 records if there is a "child" in t2
> present.
> Does somebody have any ideas? Thanks in advance.
You can use ap pair of triggers to keep the referential integrity.
example:
create table master ( mid int4 not null, name text);
create unique index master_idx on master(mid);
/* foreign key mid in detail references the primary key mid in master */
create table detail ( did int4 not null, name text, mid int4 not null);
create unique index detail_idx on detail(did);
/* allow PL/pgSQL procedures */
create function plpgsql_call_handler () returns opaque as '/usr/local/pgsql/lib/plpgsql.so' language 'C';
create trusted procedural language 'plpgsql' handler plpgsql_call_handler lancompiler 'PL/pgSQL';
/* handle delete and update in master */
create function del_master_fun () returns opaque as ' declare id int4; begin select did into id from detail d
where d.mid = old.mid; if found then raise exception ''cannot %'', tg_op; end if; if tg_op = ''DELETE''
then return old; else return new; end if; end;
' language 'plpgsql';
create trigger del_master_trg before delete or update on master for each row execute procedure del_master_fun();
/* handle insert and update in detail */
create function ins_detail_fun () returns opaque as ' declare id int4; begin select mid into id from master m
where m.mid = new.mid; if not found then raise exception ''cannot %'', tg_op; end if; return new; end;
' language 'plpgsql';
create trigger ins_detail_trg before insert or update on detail for each row execute procedure ins_detail_fun();
I hope this will help you.
Gerhard
