1 files changed, 37 insertions, 0 deletions
diff --git a/app/models/group_membership.rb b/app/models/group_membership.rb
new file mode 100644
index 0000000..0f04ae1
--- /dev/null
+++ b/app/models/group_membership.rb
@@ -0,0 +1,37 @@
+class GroupMembership < ActiveRecord::Base
+  attr_accessible :group_id, :item_type, :item_id
+
+  belongs_to :group
+  belongs_to :item, :polymorphic => true
+
+  validates :item_id,
+            :presence => true,
+            :uniqueness => { :scope => [:group_id, :item_type] }
+
+  validates :item_type,
+            :presence => true,
+            :uniqueness => { :scope => [:group_id, :item_id] }
+
+  validate  :validate_item_type_consitency
+
+  validates :item,
+            :presence => true
+
+  def to_s
+    "#{self.item_type}: #{self.item}"
+  end
+
+  def item_type_allowed
+    fist_item = self.group.group_memberships.first.try(:item)
+    if fist_item
+      return fist_item.class.name
+    end
+  end
+
+  def validate_item_type_consitency
+    type_allowed = self.item_type_allowed
+    if type_allowed && type_allowed != self.item_type
+      errors.add(:item_type, "must be of type: #{type_allowed}")
+    end
+  end
+end