diff --git a/app/models/group_user.rb b/app/models/group_user.rb
new file mode 100644
--- /dev/null
+++ b/app/models/group_user.rb
@@ -0,0 +1,7 @@
+class GroupUser < ActiveRecord::Base
+  self.table_name = 'groups_users'
+  
+  belongs_to :user
+  belongs_to :group
+  validates_uniqueness_of :user_id, scope: :group_id, message: ->(object, data) { "'#{User.find(data[:value]).full_name}' is already in the group" }
+end