Add trigger to update label positions before insert and delete

packages/db/migrations/0090.do.add_position_to_labels.sql

@@ -20,6 +20,25 @@ WITH positions AS (
   WHERE
       omnivore.labels.id = positions.id;
 
-ALTER TABLE omnivore.labels ADD constraint labels_position_user_id_unique UNIQUE(user_id, position);
+CREATE OR REPLACE FUNCTION update_label_position()
+    RETURNS TRIGGER AS $$
+    DECLARE
+        new_position INTEGER;
+    BEGIN
+        IF (TG_OP = 'DELETE') THEN
+            UPDATE omnivore.labels SET position = position - 1 WHERE user_id = OLD.user_id AND position > OLD.position;
+            RETURN OLD;
+        ELSIF (TG_OP = 'INSERT') THEN
+            SELECT MAX(position) + 1 INTO new_position FROM omnivore.labels WHERE user_id = NEW.user_id;
+            NEW.position = new_position;
+            RETURN NEW;
+        END IF;
+    END;
+$$ LANGUAGE 'plpgsql';
+
+CREATE TRIGGER update_label_position
+    BEFORE INSERT OR DELETE ON omnivore.labels
+    FOR EACH ROW
+    EXECUTE FUNCTION update_label_position();
 
 COMMIT;

packages/db/migrations/0090.undo.add_position_to_labels.sql

@@ -4,6 +4,10 @@
 
 BEGIN;
 
+DROP TRIGGER IF EXISTS update_label_position ON omnivore.labels;
+
+DROP FUNCTION IF EXISTS update_label_position;
+
 ALTER TABLE omnivore.labels DROP COLUMN IF EXISTS position;
 
 COMMIT;