Postgres - Create trigger that can exist in multiple schemas - postgresql

Question

I have a postgres trigger that I have written. It works 100%, I've tested it thoroughly. However, when my application writes to that database table, it fails. I'll put the code below, then I'll explain the failure.
CREATE OR REPLACE FUNCTION validate_client_user_role()
RETURNS trigger AS
$BODY$
DECLARE role_has_client INT;
DECLARE user_has_client INT;
BEGIN
IF NEW.client_id IS NULL THEN
RAISE EXCEPTION 'client_id cannot be null';
END IF;
IF NEW.user_id IS NULL THEN
RAISE EXCEPTION 'user_id cannot be null';
END IF;
IF NEW.role_id IS NULL THEN
RAISE EXCEPTION 'role_id cannot be null';
END IF;
SELECT COUNT(*)
INTO role_has_client
FROM roles
WHERE id = NEW.role_id
AND client_id = NEW.client_id;
SELECT COUNT(*)
INTO user_has_client
FROM client_users
WHERE user_id = NEW.user_id
AND client_id = NEW.client_id;
IF role_has_client = 0 THEN
RAISE EXCEPTION 'Role is not allowed by client';
END IF;
IF user_has_client = 0 THEN
RAISE EXCEPTION 'User is not allowed by client';
END IF;
RETURN NEW;
END
$BODY$ LANGUAGE plpgsql;
CREATE TRIGGER client_user_role_validation
BEFORE INSERT OR UPDATE
ON client_user_roles
FOR EACH ROW
EXECUTE PROCEDURE validate_client_user_role();
So, my application database has multiple schemas, one for dev, qa, prod, etc. When I first write this DDL statement, I run this first:
set search_path to dev;
This then adds it properly to the "dev" schema. As long as I'm in my DB query console, I can validate this trigger is working perfectly.
However, when my application tries to write to the tables, the trigger fails, saying the relations (roles, client_users) that it tries to do selects from don't exist. I can fix this by modifying the function code to explicitly reference the "dev" schema for each table. I don't want to do this, though. I would prefer code that I can execute as a DDL statement for dev/qa/prod without needing to replace all the schema references or keep multiple copies of it.
I'm hoping someone can explain if there is some way to do this. Obviously the trigger is not inheriting from the schema it is assigned to when I execute it. However, if there is some postgres trick I'm not aware of to make this work, I would appreciate the guidance. Thank you.

Answer 1

You can use the TG_TABLE_SCHEMA variable and set_config() with IS_LOCAL = true to accomplish this:
CREATE OR REPLACE FUNCTION validate_client_user_role()
RETURNS trigger AS
$BODY$
DECLARE role_has_client INT;
DECLARE user_has_client INT;
BEGIN
IF NEW.client_id IS NULL THEN
RAISE EXCEPTION 'client_id cannot be null';
END IF;
IF NEW.user_id IS NULL THEN
RAISE EXCEPTION 'user_id cannot be null';
END IF;
IF NEW.role_id IS NULL THEN
RAISE EXCEPTION 'role_id cannot be null';
END IF;
PERFORM set_config('search_path', TG_TABLE_SCHEMA, true); -- <-- This line
SELECT COUNT(*)
INTO role_has_client
FROM roles
WHERE id = NEW.role_id
AND client_id = NEW.client_id;
SELECT COUNT(*)
INTO user_has_client
FROM client_users
WHERE user_id = NEW.user_id
AND client_id = NEW.client_id;
IF role_has_client = 0 THEN
RAISE EXCEPTION 'Role is not allowed by client';
END IF;
IF user_has_client = 0 THEN
RAISE EXCEPTION 'User is not allowed by client';
END IF;
RETURN NEW;
END
$BODY$ LANGUAGE plpgsql;