Implement related events

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

priv/repo/migrations/20190411161557_event_event_tag_on_delete.exs

@@ -0,0 +1,23 @@
+defmodule Mobilizon.Repo.Migrations.EventEventTagOnDelete do
+  use Ecto.Migration
+
+  def up do
+    drop(constraint(:events_tags, "events_tags_event_id_fkey"))
+    drop(constraint(:events_tags, "events_tags_tag_id_fkey"))
+
+    alter table(:events_tags) do
+      modify(:event_id, references(:events, on_delete: :delete_all))
+      modify(:tag_id, references(:tags, on_delete: :delete_all))
+    end
+  end
+
+  def down do
+    drop(constraint(:events_tags, "events_tags_event_id_fkey"))
+    drop(constraint(:events_tags, "events_tags_tag_id_fkey"))
+
+    alter table(:events_tags) do
+      modify(:event_id, references(:events))
+      modify(:tag_id, references(:tags))
+    end
+  end
+end