Appling Constraints To Avoid Cyclic In Oracle

Question

Hi Guys,
I have a table category_defn ,In this table there are 3 columns category_id,parent_category_id,bank_id.
I have a requirement like if 1 has two children 2 and 3 , I need to have a constraint which will restrict the data entry
1 as a child of 3.That means it should not allow the cyclic order in the parent and child
I am wondering is there any constraint or way to achieve this in Oracle with out the help of triggers.
Any ideas,suggestions will be highly appreciated.
Thanks,
Papi

Answer 1

957590 wrote:
Is there any way even if in the complex manner to achieve this.Here's a try. It seems to "work", but it makes the hierarchy much harder to change.
The idea is:
- Use purely technical IDs for primary key and parent
- Never allow a parent id to be greater than a child id (check constraint)
- Have your "real" category_id be UNIQUE.
- Make the constraint on the "real" id DEFERRABLE so you can update it.drop sequence s;
create sequence s;
drop table t;
create table t (
  tech_id number primary key,
  parent_tech_id number,
  category_id number unique deferrable,
  check(parent_tech_id < tech_id)
alter table t add constraint fk_t
foreign key (parent_tech_id) references t(tech_id);
insert into t values(s.nextval,null, 1);
insert into t values(s.nextval,(select max(tech_id) from t), 2);
insert into t values(s.nextval,(select max(tech_id) from t), 3);
select * from t;
   TECH_ID PARENT_TECH_ID CATEGORY_ID
         1                          1
         2              1           2
         3              2           3 Test of the check constraint:update t set parent_tech_id = 3 where tech_id = 1;
SQL Error: ORA-02290: check constraint (STEW.SYS_C0034169) violatedUpdate the "real" IDset constraints all deferred;
update t set category_id =
case category_id when 1 then 3 when 3 then 1 end
where category_id in(1,3);
set constraints all immediate;
commit;The drawback to this idea is that some changes to the hierarchy are harder to do. What if you have lots of descendants and you just want to put the ancestor under a newer row? You either have to manually adjust the TECH_ID of the newer row, or do lots of UPDATEs, or do lots of DELETEs + INSERTs. Does this solution reduce complexity or just move it somewhere else?
At least with this solution you don't need triggers!
P.S. I did this "quick and dirty". In real life, always put names on deferrable constraints so you can defer them by name.
Edited by: Stew Ashton on Jan 28, 2013 1:44 PM