add option to support specifying reverse association field

lib/couchrest/model/associations.rb

@@ -111,9 +111,11 @@ def associations
         private
 
         def merge_belongs_to_association_options(attrib, options = nil)
+          class_name = options.delete(:class_name) if options.is_a?(Hash)
+          class_name ||= attrib
           opts = {
             :foreign_key => attrib.to_s.singularize + '_id',
-            :class_name  => attrib.to_s.singularize.camelcase,
+            :class_name  => class_name.to_s.singularize.camelcase,
             :proxy_name  => attrib.to_s.pluralize,
             :allow_blank => false
           }
@@ -161,9 +163,9 @@ def #{attrib}=(value)
                 self.#{options[:foreign_key]} = value.nil? ? nil : value.id
               unless value.nil?
                 binding = value
-                binding.set_back_association(self, self.class.name)
+                binding.set_back_association(self, self.class.name, '#{options[:reverse_association]}')
               else
-                binding.set_back_association(nil, self.class.name)
+                binding.set_back_association(nil, self.class.name, '#{options[:reverse_association]}')
               end
               register_dirty_association(binding)
               @#{attrib} = value
@@ -193,14 +195,23 @@ def #{attrib}=(value)
 
       end
 
-      def set_back_association(value, class_name)
-        assoc = self.class.associations.detect { |ass| ass[:options][:class_name] == class_name }
-        return unless assoc
-        case assoc[:type]
-        when :belongs_to
-          send("#{assoc[:options][:foreign_key]}=", (value.nil? ? nil : value.id))
-        when :collection_of
-          instance_eval("#{assoc[:options][:foreign_key]}.push('#{value.nil? ? nil : value.id}')")
+      def set_back_association(value, class_name, reverse_association = nil)
+        if reverse_association && !reverse_association.empty?
+          prop = self.class.properties.detect { |prop|  prop.name =~ %r{#{reverse_association}_id} }
+          if prop.type.ancestors.include? Enumerable
+            instance_eval("#{prop.name}.push('#{value.nil? ? nil : value.id}')")
+          else
+            send("#{prop.name}=", (value.nil? ? nil : value.id))
+          end
+        else
+          assoc = self.class.associations.detect { |ass| ass[:options][:class_name] == class_name }
+          return unless assoc
+          case assoc[:type]
+          when :belongs_to
+            send("#{assoc[:options][:foreign_key]}=", (value.nil? ? nil : value.id))
+          when :collection_of
+            instance_eval("#{assoc[:options][:foreign_key]}.push('#{value.nil? ? nil : value.id}')")
+          end
         end
       end
 

spec/fixtures/models/kid.rb

@@ -1,7 +1,7 @@
 class  Kid < CouchRest::Model::Base
   property :name, String
 
-  belongs_to :dad, :class_name => 'Husband'
-  belongs_to :mum, :class_name => 'Wife'
+  belongs_to :dad, :class_name => 'Parent'
+  belongs_to :mum, :class_name => 'Parent'
 
 end

spec/fixtures/models/parent.rb

@@ -0,0 +1,10 @@
+class  Parent < CouchRest::Model::Base
+  property :name, String
+
+  belongs_to :super_power
+  belongs_to :husband, :class_name => :parent, :reverse_association => :wife
+  belongs_to :wife, :class_name => :parent, :reverse_association => :husband
+  belongs_to :lives_with, :class_name => :parent, :reverse_association => :lives_with
+
+  collection_of :children, :class_name => 'Kid'
+end

spec/fixtures/models/super_power.rb

@@ -0,0 +1,5 @@
+class SuperPower < CouchRest::Model::Base
+  property :description, String
+
+  belongs_to :parent
+end

spec/unit/assocations_dual_spec.rb

@@ -3,28 +3,40 @@
 
 describe 'Associations' do
 
-  let(:father) { Husband.create(name: 'bob')}
-  let(:mummy)  { Wife.create(   name: 'claire')}
+  let(:father) { Parent.create(name: 'Bob')}
+  let(:can_fly){ SuperPower.create(description: 'Can fly when there is no cloud')}
+  let(:mummy)  { Parent.create(   name: 'Claire')}
   let(:kid)    { Kid.create(    name: 'Vladimir')}
 
   describe 'of type belongs_to' do
     context 'with the other side also belongs_to (1-1)' do
-      it 'should set the other side property too' do
-        father.wife = mummy
-        mummy.husband.should eql(father)
+      context '[non ambiguous association]' do
+        it 'should set the other side property too' do
+          father.super_power = can_fly
+          can_fly.parent.should eql father
+        end
       end
 
-      it 'should remove the other side if value is nil' do
-        father.wife = mummy
-        father.wife = nil
-        mummy.husband.should be_nil
+      context '[ambiguous association]' do
+        it 'should set the other side property too' do
+          father.wife = mummy
+          mummy.husband.should eql(father)
+        end
+      end
+
+      context '[cyclic association]' do
+        it 'should set the other side property too' do
+          father.lives_with = mummy
+          mummy.lives_with.should eql(father)
+        end
       end
     end
 
     context 'with the other side do not back associate (1-0)' do
       let(:invoice) { SaleInvoice.create(:price => 2000) }
       let(:client)  { Client.create(:name => "Sam Lown") }
       it 'should set property without error' do
+        invoice.client = client
         lambda { invoice.client = client }.should_not raise_error
       end