Make actors deletion cascade to followers

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

priv/repo/migrations/20191023133805_delete_actors_cascade_to_followers.exs

@@ -0,0 +1,23 @@
+defmodule Mobilizon.Storage.Repo.Migrations.DeleteActorsCascadeToFollowers do
+  use Ecto.Migration
+
+  def up do
+    drop(constraint(:followers, "followers_actor_id_fkey"))
+    drop(constraint(:followers, "followers_target_actor_id_fkey"))
+
+    alter table(:followers) do
+      modify(:actor_id, references(:actors, on_delete: :delete_all))
+      modify(:target_actor_id, references(:actors, on_delete: :delete_all))
+    end
+  end
+
+  def down do
+    drop(constraint(:followers, "followers_actor_id_fkey"))
+    drop(constraint(:followers, "followers_target_actor_id_fkey"))
+
+    alter table(:followers) do
+      modify(:actor_id, references(:actors, on_delete: :nothing))
+      modify(:target_actor_id, references(:actors, on_delete: :nothing))
+    end
+  end
+end