DB migration to include visualization_id in the assets table

db/migrate/20190521171900_add_visualization_id_assets.rb

@@ -0,0 +1,22 @@
+require 'carto/db/migration_helper'
+
+include Carto::Db::MigrationHelper
+
+migration(
+  Proc.new do
+    alter_table :assets do
+      add_foreign_key :visualization_id,
+                      :visualizations,
+                      type: :uuid,
+                      on_delete: :cascade
+
+      add_index [:visualization_id]
+    end
+  end,
+  Proc.new do
+    alter_table :assets do
+      drop_index :visualization_id
+      drop_column :visualization_id
+    end
+  end
+)