Does anyone know how I can make a constraint on a key to enforce a 1
to n relationship where n>0?
I've invented an example to show the sort of constraint I need:
CREATE TABLE permissions (
id int4,
userid int4,
perm int4,
primary key (id,userid)
);
CREATE TABLE objects (
id int4,
perm int4 NOT NULL,
data text
);
INSERT INTO permissions (id,userid,perm) VALUES (1,1001,7);
INSERT INTO permissions (id,userid,perm) VALUES (1,1002,6);
INSERT INTO permissions (id,userid,perm) VALUES (1,1003,4);
INSERT INTO permissions (id,userid,perm) VALUES (2,1001,0);
So I want to allow something like:
INSERT INTO objects (id,perm,data) VALUES (1,1,'everyone can read');
INSERT INTO objects (id,perm,data) VALUES (2,1,'everyone can read');
INSERT INTO objects (id,perm,data) VALUES (3,2,'nobody can read');
But disallow an insert like:
INSERT INTO objects (id,perm,data) VALUES (9999,1,'bad perm example');
Is this possible?
-Michael
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