Add lazy support for scopes with different foreign key names

README.md

@@ -25,9 +25,13 @@ class Item
   include Mongoid::Orderable
 
   # belongs_to :group
+  # belongs_to :drawer, :class_name => "Office::Drawer",
+  #            :foreign_key => "legacy_drawer_key_id"
 
   # orderable
   # orderable :scope => :group, :column => :pos
+  # be lazy with different foreign keys
+  # orderable :scope => drawer, :column => :pos
   # orderable :scope => lambda { |document| where(:group_id => document.group_id) }
   # orderable :index => false # this one if you want specify indexes manually
   # orderable :base => 0 # count position from zero as the top-most value (1 is the default value)

lib/mongoid/orderable.rb

@@ -11,7 +11,15 @@ def orderable options = {}
       }
 
       configuration.merge! options if options.is_a?(Hash)
-      configuration[:scope] = "#{configuration[:scope]}_id".to_sym if configuration[:scope].is_a?(Symbol) && configuration[:scope].to_s !~ /_id$/
+
+      if configuration[:scope].is_a?(Symbol) && configuration[:scope].to_s !~ /_id$/
+        scope_relation = self.relations[configuration[:scope].to_s]
+        if scope_relation
+          configuration[:scope] = scope_relation.key.to_sym
+        else
+          configuration[:scope] = "#{configuration[:scope]}_id".to_sym
+        end
+      end
 
       field configuration[:column], orderable_field_opts(configuration)
       if configuration[:index]

spec/mongoid/orderable_spec.rb

@@ -74,6 +74,16 @@ class Apple < Fruit
   class Orange < Fruit
   end
 
+  class ForeignKeyDiffersOrderable
+    include Mongoid::Document
+    include Mongoid::Orderable
+
+    belongs_to  :different_scope, :class_name => "ForeignKeyDiffersOrderable",
+                :foreign_key => "different_orderable_id"
+
+    orderable :scope => :different_scope
+  end
+
   describe SimpleOrderable do
 
     before :each do
@@ -558,4 +568,21 @@ def positions
       fruit2.position.should == 2
     end
   end
+
+  describe ForeignKeyDiffersOrderable do
+
+    it 'uses the foreign key of the relationship as scope' do
+      orderable1, orderable2, orderable3 = nil
+      parent_scope1 = ForeignKeyDiffersOrderable.create
+      parent_scope2 = ForeignKeyDiffersOrderable.create
+      expect do
+        orderable1 = ForeignKeyDiffersOrderable.create(:different_scope => parent_scope1)
+        orderable2 = ForeignKeyDiffersOrderable.create(:different_scope => parent_scope1)
+        orderable3 = ForeignKeyDiffersOrderable.create(:different_scope => parent_scope2)
+      end.to_not raise_error
+      expect(orderable1.position).to eq 1
+      expect(orderable2.position).to eq 2
+      expect(orderable3.position).to eq 1
+    end
+  end
 end