User_roles table constraints

backend/internal/database/migrations/0050_user_roles.sql

@@ -4,4 +4,13 @@ CREATE TABLE IF NOT EXISTS user_roles (
   role STRING NOT NULL, -- 'admin' or 'member'
   FOREIGN KEY (user_id) REFERENCES users (id)
   FOREIGN KEY (project_id) REFERENCES projects (id)
+  PRIMARY KEY (user_id, project_id)
 );
+
+-- Make sure that the role is either 'admin' or 'member'
+CREATE TRIGGER IF NOT EXISTS user_role_admin_or_member
+  BEFORE INSERT ON user_roles
+  FOR EACH ROW
+  BEGIN
+    SELECT RAISE(ABORT, 'Invalid role') WHERE NEW.role NOT IN ('admin', 'member');
+  END;