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