Foreign keys + table inheritance in PostgreSQL?

Question

I have three tables: organization, organization_teams and org_users. Here organization_teams is inherited from organization. So suppose if a record is added in organizations_teams it will get the organization table id as value for id column in organization_teams.

org_users has foreign key on id column of organization. Now when I try to insert data in org_users it giving me error as below

insert or update on table "org_users" violates foreign key constraint "org_users_organizations"
DETAIL:  Key (org_id)=(12) is not present in table "organizations"

Why?

Solution 1

It's covered in the user manual.

The short version: you can use foreign keys, or table inheritance, but not both. This isn't inherently impossible, it's just that it's technically quite difficult to implement unique indexes that span inherited tables in PostgreSQL in a fast, reliable manner. Without that, you can't have a useful foreign key. Nobody's successfully implemented it well enough for a patch adding support to be accepted into PostgreSQL yet.

A foreign key can point to a table that is part of an inheritance hierarchy, but it'll only find rows in that table exactly. Not in any parent or child tables. To see which rows the foreign key sees, do a SELECT * FROM ONLY thetable. The ONLY keyword means "ignoring inheritance" and that's what the foreign key lookup will do.

Solution 2

The only workaround i have found is:

1. create function returning trigger for checking existence of some id in inherited table
2. create a constraint trigger instead of FK

Comments

[Andrew Wolfe]

Would it be 'safe' to only apply foreign keys at the 'leaf' tables of a table inheritance hierarchy?

[Craig Ringer]

@AndrewWolfe If referencing and referenced tables are partitioned on the same key you can have FKs between corresponding partitions. That's about all.