Make sure m:m joins join with the FK of the inner association properly

[#903 state:resolved]

lib/dm-core/query/conditions/comparison.rb

@@ -471,8 +471,10 @@ def matches?(record)
         #
         # @api semipublic
         def foreign_key_mapping
-          inverse = subject.inverse
-          Query.target_conditions(value, inverse.source_key, inverse.target_key)
+          relationship = subject.inverse
+          relationship = relationship.links.first if relationship.respond_to?(:links)
+
+          Query.target_conditions(value, relationship.source_key, relationship.target_key)
         end
 
         private

spec/public/associations/many_to_many/read_multiple_join_spec.rb

@@ -0,0 +1,67 @@
+require File.expand_path(File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper'))
+
+describe 'Many to Many Associations read across multiple join associations' do
+  before :all do
+    class User
+      include DataMapper::Resource
+
+      property :id, Serial
+
+      has n, :sales
+      has n, :sale_items, :through => :sales
+      has n, :items,      :through => :sale_items
+    end
+
+    class Sale
+      include DataMapper::Resource
+
+      property :id, Serial
+
+      belongs_to :user
+      has n, :sale_items
+      has n, :items, :through => :sale_items
+    end
+
+    class SaleItem
+      include DataMapper::Resource
+
+      property :id, Serial
+
+      belongs_to :sale
+      belongs_to :item
+    end
+
+    class Item
+      include DataMapper::Resource
+
+      property :id, Serial
+
+      has n, :sale_items
+    end
+  end
+
+  supported_by :all do
+    before :all do
+      @user = User.create
+      @sale = @user.sales.create
+
+      5.times { @sale.items.create }
+    end
+
+    before :all do
+      @no_join = defined?(DataMapper::Adapters::InMemoryAdapter) && @adapter.kind_of?(DataMapper::Adapters::InMemoryAdapter) ||
+                 defined?(DataMapper::Adapters::YamlAdapter)     && @adapter.kind_of?(DataMapper::Adapters::YamlAdapter)
+
+      @skip = @no_join
+    end
+
+    before do
+      pending if @skip
+    end
+
+    it 'should return all the created entries' do
+      @user.items.to_a.should == Item.all.to_a
+      @sale.items.to_a.should == Item.all.to_a
+    end
+  end
+end