PostgreSQL FOREIGN KEY with second database

Question

I'm running the following queries on PostgreSQL 9.3:

CREATE TABLE "app_item" 
  ( 
     "id"          SERIAL NOT NULL PRIMARY KEY, 
     "location_id" UUID NOT NULL 
  ); 

CREATE INDEX app_item_e274a5da 
  ON "app_item" ("location_id"); 

ALTER TABLE "app_item" 
  ADD CONSTRAINT app_item_location_id_5cecc1c0b46e12e2_fk_fias_addrobj_aoguid 
  FOREIGN KEY ("location_id") REFERENCES "fias_addrobj" ("aoguid") deferrable 
  initially deferred;

Third query returns:

ERROR: relation "fias_addrobj" does not exist

• app_item - table in first database
• fias_addrobj - table in second database

How to do correct query with this databases?

Answer 1

I've not had occasion to use this myself, but you might want to look into Foreign Data Wrappers , which are essentially the successor to dblink . In particular, postgres-fdw .

Once the general setup of the fdw is in place (steps 1-3 in the link above), you could create a foreign table via CREATE FOREIGN TABLE , defined like the table in your remote DB, and then use that table as part of the foreign key CONSTRAINT , and see if it works.

If that doesn't work, another option would be to have a process which ETL's the data (say, via a Python script) from the remote server over to the local server (say, on an hourly or daily basis, depending on the size), and then you would have a true local table to use in the foreign key CONSTRAINT . It wouldn't be real-time, but depending on your needs, may suffice.

Answer 2

A local table must be referenced

However, as stated within the below link, you could maybe use a trigger which uses a cross server join (facilitated by dblink ) to simulate the built-in methods for constraining?

For instance, you could have a trigger set up that on INSERT , checks to see if a given FK exists to aid with enforcing referential integrity, or on DELETE to cascade

http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=101322

PS Would avoid this at all costs.