How to make a foreign key with a constraint on the referenced table in PostgreSQL

Question

Suppose I have the following tables

CREATE TABLE plugins (
id int primary key,
type text);

insert into plugins values (1,\'matrix\');
insert into plugins va         


        

Answer 1

Use a compound key in the referenced table and a CHECK constraint in the referencing table e.g.

CREATE TABLE plugins (
id int primary key,
type text, 
UNIQUE (type, id)
);

CREATE TABLE matrix_params (
id int primary key,
plugintype text DEFAULT 'matrix' NOT NULL
   CHECK (plugintype = 'matrix'),
pluginid int NOT NULL,
FOREIGN KEY (plugintype, pluginid)
   references plugins (type, id)
);