Make media subscriptions unique

platform/priv/repo/migrations/20231120174841_make_subscriptions_unique.exs

@@ -0,0 +1,22 @@
+defmodule Platform.Repo.Migrations.MakeSubscriptionsUnique do
+  use Ecto.Migration
+
+  def change do
+    # Delete all non-unique media_subscriptions
+    execute """
+    WITH CTE AS (
+        SELECT
+            id,
+            ROW_NUMBER() OVER (PARTITION BY user_id, media_id ORDER BY inserted_at) as rn
+        FROM
+        media_subscriptions
+    )
+    DELETE FROM
+      media_subscriptions
+    WHERE
+      id IN (SELECT id FROM CTE WHERE rn > 1)
+    """
+
+    create unique_index(:media_subscriptions, [:user_id, :media_id])
+  end
+end