Fix Mongoid has_many association _ids helper issue

- fix #332

lib/aasm/persistence/mongoid_persistence.rb

@@ -96,7 +96,13 @@ module AASM
         #
         def aasm_ensure_initial_state
           AASM::StateMachine[self.class].keys.each do |state_machine_name|
-            send("#{self.class.aasm(state_machine_name).attribute_name}=", aasm(state_machine_name).enter_initial_state.to_s) if send(self.class.aasm(state_machine_name).attribute_name).blank?
+            attribute_name = self.class.aasm(state_machine_name).attribute_name.to_s
+            # Do not load initial state when object attributes are not loaded,
+            # mongoid has_many relationship does not load child object attributes when
+            # only ids are loaded, for example parent.child_ids will not load child object.
+            if attribute_names.include?(attribute_name) && attributes[attribute_name].blank? && !attribute_missing?(attribute_name)
+              send("#{self.class.aasm(state_machine_name).attribute_name}=", aasm(state_machine_name).enter_initial_state.to_s)
+            end
           end
         end
       end # InstanceMethods

spec/models/mongoid/mongoid_relationships.rb

@@ -0,0 +1,26 @@
+class Parent
+  include Mongoid::Document
+  include AASM
+
+  field :status, :type => String
+  has_many :childs
+
+  aasm column: :status do
+    state :unknown_scope
+    state :new
+  end
+end
+
+class Child
+  include Mongoid::Document
+  include AASM
+  field :parent_id
+
+  field :status, :type => String
+  belongs_to :parent
+
+  aasm column: :status do
+    state :unknown_scope
+    state :new
+  end
+end

spec/unit/persistence/mongoid_persistence_spec.rb

@@ -71,6 +71,17 @@ describe 'mongoid' do
 
     end
 
+    describe "relations object" do
+
+      it "should load relations object ids" do
+        parent  =  Parent.create
+        child_1 = Child.create(parent_id: parent.id)
+        child_2 = Child.create(parent_id: parent.id)
+        expect(parent.child_ids).to eql [child_1.id, child_2.id]
+      end
+
+    end
+
   rescue LoadError
     puts "--------------------------------------------------------------------------"
     puts "Not running Mongoid specs because mongoid gem is not installed!!!"