FEATURE: backend for inviting a user to a group

db/migrate/20140508053815_add_invited_groups.rb

@@ -0,0 +1,9 @@
+class AddInvitedGroups < ActiveRecord::Migration
+  def change
+    create_table :invited_groups do |t|
+      t.integer :group_id
+      t.integer :invite_id
+      t.timestamps
+    end
+  end
+end