db migration to add index on user_id of user_assets table

ruby/db/migrate/20210611200219_add_index_on_user_assets_user_id.rb

@@ -0,0 +1,9 @@
+  class AddIndexOnUserAssetsUserId < ActiveRecord::Migration
+    def self.up
+      execute("CREATE INDEX index_user_assets_user_id ON public.user_assets USING btree (user_id);");
+    end
+
+    def self.down
+      execute("DROP INDEX index_user_assets_user_id")
+    end
+  end