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Thread: State of the art for foreign keys to child tables?

State of the art for foreign keys to child tables?

From
François Beausoleil
Date:
What's the state of the art for foreign keys on child tables?

My use case is this:

CREATE TABLE parties(party_id serial primary key);
CREATE TABLE positions( PRIMARY KEY(party_id) ) INHERITS(parties);
CREATE TABLE organizations( PRIMARY KEY(party_id) ) INHERITS(parties);
CREATE TABLE party_names( party_id int REFERENCES parties, surname text, PRIMARY KEY(party_id, surname) );

INSERT INTO organizations VALUES (1);
INSERT INTO party_names VALUES (1, 'foo');

This currently fails with:

ERROR:  insert or update on table "party_names" violates foreign key constraint "party_names_party_id_fkey"
DETAIL:  Key (party_id)=(1) is not present in table "parties".

I found http://stackoverflow.com/questions/10252603/parent-and-child-table-foreign-key which suggests using something like this:

CREATE RULE parties_ref
AS ON INSERT TO party_names
WHERE new.party_id NOT IN (SELECT party_id FROM parties)
DO INSTEAD NOTHING;

When using that and no foreign key reference, then the INSERT "succeeds" in inserting 0 records, which doesn't raise an exception... Then I found older posts on this mailing list:


These mention using triggers to reproduce foreign key checks.

Is that information still current as of 9.2?

Thanks!
François

Re: State of the art for foreign keys to child tables?

From
"Albe Laurenz"
Date:
François Beausoleil wrote:
> What's the state of the art for foreign keys on child tables?
>
> My use case is this:
>
>
> CREATE TABLE parties(party_id serial primary key);
> CREATE TABLE positions( PRIMARY KEY(party_id) ) INHERITS(parties);
> CREATE TABLE organizations( PRIMARY KEY(party_id) ) INHERITS(parties);
> CREATE TABLE party_names( party_id int REFERENCES parties, surname text, PRIMARY KEY(party_id,
> surname) );
>
> INSERT INTO organizations VALUES (1);
> INSERT INTO party_names VALUES (1, 'foo');
>
> This currently fails with:
>
> ERROR:  insert or update on table "party_names" violates foreign key constraint
> "party_names_party_id_fkey"
> DETAIL:  Key (party_id)=(1) is not present in table "parties".
>
> I found http://stackoverflow.com/questions/10252603/parent-and-child-table-foreign-key which suggests
> using something like this:
>
> CREATE RULE parties_ref
> AS ON INSERT TO party_names
> WHERE new.party_id NOT IN (SELECT party_id FROM parties)
> DO INSTEAD NOTHING;
>
> When using that and no foreign key reference, then the INSERT "succeeds" in inserting 0 records, which
> doesn't raise an exception... Then I found older posts on this mailing list:
>
> http://postgresql.1045698.n5.nabble.com/Foreign-keys-to-inherited-tables-td1900234.html
> http://postgresql.1045698.n5.nabble.com/Inheritance-on-foreign-key-td1924951.html
> http://postgresql.1045698.n5.nabble.com/Partitioned-Tables-Foreign-Key-Constraints-Problem-
> td2066267.html
>
> These mention using triggers to reproduce foreign key checks.
>
> Is that information still current as of 9.2?

I'm afraid that a trigger is still the best you can do.

Yours,
Laurenz Albe