Row level security is a great Postgres feature that allows to grant privileges to selected rows only, without having to create additional data structures. The common setup is to add a column with users’ names, and a policy that compares this column value with CURRENT_USER:
CREATE TABLE issues(id integer generated always as identity primary key, title varchar, description varchar, status varchar, assignee varchar); ALTER TABLE issues ENABLE ROW LEVEL SECURITY; CREATE POLICY issue_rls ON issues FOR ALL TO public USING (assignee = CURRENT_USER);
And then, any user that isn’t a superuser or hasn’t the BYPASSRLS privilege will see (and be able to edit) only rows with relevant “assignee” value. And it works well in an environment with only handful of users. But as the number of users grow, it can become difficult to maintain: sometimes we’ll want to assign some rows to multiple users, or a whole group of users. What to do then?
Enter the pg_has_role function. It checks if a particular user has given role. Its usage is quite simple:
SELECT pg_has_role('chinook', 'service', 'USAGE');
the first argument is the user name, the second is a role name, and the third is a bit tricky: ‘MEMBER’ determines if user is an actual member of role or can execute SET ROLE to become a member, while ‘USAGE’ checks for actual membership only. As users are in fact specific case of roles with LOGIN privilege (for very old Postgres versions – 8.0 and earlier – this isn’t true, but those versions don’t have row level security anyway) , this function works equally well for individual users and group roles.
So, we’ll modify the policy as such:
DROP POLICY issue_rls; CREATE POLICY issue_rls ON issues FOR ALL TO public USING (pg_has_role(current_user, assignee, 'USAGE'));
…and now the rows can be assigned to individual users or whole roles.