From 9ee697c533d2d1c0093a8621313fcc4f19f8e575 Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Tue, 20 Jan 2015 18:49:06 +0000
Subject: [PATCH 01/21] [back_assignments] create fixture models and spec
 titles

---
 spec/fixtures/models/husband.rb    |  7 +++++++
 spec/fixtures/models/kid.rb        |  7 +++++++
 spec/fixtures/models/sale_entry.rb |  2 +-
 spec/fixtures/models/wife.rb       |  7 +++++++
 spec/unit/assocations_dual_spec.rb | 22 ++++++++++++++++++++++
 spec/unit/assocations_spec.rb      |  2 +-
 6 files changed, 45 insertions(+), 2 deletions(-)
 create mode 100644 spec/fixtures/models/husband.rb
 create mode 100644 spec/fixtures/models/kid.rb
 create mode 100644 spec/fixtures/models/wife.rb
 create mode 100644 spec/unit/assocations_dual_spec.rb

diff --git a/spec/fixtures/models/husband.rb b/spec/fixtures/models/husband.rb
new file mode 100644
index 00000000..d5434fa4
--- /dev/null
+++ b/spec/fixtures/models/husband.rb
@@ -0,0 +1,7 @@
+class  Husband < CouchRest::Model::Base
+  property :name, [String]
+
+  belongs_to :wife
+
+  collection_of :children, :class_name => 'Kid'
+end
diff --git a/spec/fixtures/models/kid.rb b/spec/fixtures/models/kid.rb
new file mode 100644
index 00000000..bb81baff
--- /dev/null
+++ b/spec/fixtures/models/kid.rb
@@ -0,0 +1,7 @@
+class  Kid < CouchRest::Model::Base
+  property :name, [String]
+
+  belongs_to :dad, :class_name => 'Husband'
+  belongs_to :mum, :class_name => 'Wife'
+
+end
diff --git a/spec/fixtures/models/sale_entry.rb b/spec/fixtures/models/sale_entry.rb
index 4c4b8e38..30741dbc 100644
--- a/spec/fixtures/models/sale_entry.rb
+++ b/spec/fixtures/models/sale_entry.rb
@@ -7,5 +7,5 @@ class SaleEntry < CouchRest::Model::Base
   design do
     view :by_description
   end
-  
+
 end
diff --git a/spec/fixtures/models/wife.rb b/spec/fixtures/models/wife.rb
new file mode 100644
index 00000000..b24f5f8c
--- /dev/null
+++ b/spec/fixtures/models/wife.rb
@@ -0,0 +1,7 @@
+class  Wife < CouchRest::Model::Base
+  property :name, [String]
+
+  belongs_to :husband
+
+  collection_of :children, :class_name => 'Kid'
+end
diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
new file mode 100644
index 00000000..798a1ffc
--- /dev/null
+++ b/spec/unit/assocations_dual_spec.rb
@@ -0,0 +1,22 @@
+# encoding: utf-8
+require 'spec_helper'
+
+describe 'Associations' do
+
+  describe 'of type belongs' do
+    context 'the other side also belongs_to' do
+      it 'should set the other side property too' do
+      end
+    end
+
+    context 'the other side do not share association' do
+      it 'should set property without error' do
+      end
+    end
+
+    context 'the other side associate as a collection' do
+      it 'should be part of the collection weh setting the property' do
+      end
+    end
+  end
+end
diff --git a/spec/unit/assocations_spec.rb b/spec/unit/assocations_spec.rb
index 04e95039..2582bf3d 100644
--- a/spec/unit/assocations_spec.rb
+++ b/spec/unit/assocations_spec.rb
@@ -29,7 +29,7 @@ def SaleInvoice.merge_assoc_opts(*args)
       o = SaleInvoice.merge_assoc_opts(:cat)
       o[:proxy].should eql('self.company.cats')
     end
-    
+
   end
 
   describe "of type belongs to" do

From 9fdeae50923a0d8a7e0b3ef65d32df55de0cbcd7 Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Tue, 20 Jan 2015 18:59:10 +0000
Subject: [PATCH 02/21] [back_assignments] finish spec cases enumeration

---
 spec/unit/assocations_dual_spec.rb | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index 798a1ffc..7d437d79 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -3,20 +3,31 @@
 
 describe 'Associations' do
 
-  describe 'of type belongs' do
-    context 'the other side also belongs_to' do
+  describe 'of type belongs_to' do
+    context 'the other side also belongs_to (1-1)' do
       it 'should set the other side property too' do
       end
     end
 
-    context 'the other side do not share association' do
+    context 'the other side do not back associate (1-0)' do
       it 'should set property without error' do
       end
     end
 
-    context 'the other side associate as a collection' do
+    context 'the other side associate as a collection (1-n)' do
       it 'should be part of the collection weh setting the property' do
       end
     end
   end
+
+  descibe 'of type collection_of' do
+    context 'the other side is a belongs_to (n-1)' do
+      it 'should populate the belongs_to property when added to the collection'
+    end
+
+    context 'the other side do not back associate (n-0)' do
+      it 'should set property without error' do
+      end
+    end
+  end
 end

From 8dc8f44dba27561ba2cd21a29681b1df3de9e508 Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Tue, 20 Jan 2015 21:38:04 +0000
Subject: [PATCH 03/21] [back_assignments] simplier name for fixture models

---
 spec/fixtures/models/husband.rb | 2 +-
 spec/fixtures/models/kid.rb     | 2 +-
 spec/fixtures/models/wife.rb    | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/spec/fixtures/models/husband.rb b/spec/fixtures/models/husband.rb
index d5434fa4..291e33bc 100644
--- a/spec/fixtures/models/husband.rb
+++ b/spec/fixtures/models/husband.rb
@@ -1,5 +1,5 @@
 class  Husband < CouchRest::Model::Base
-  property :name, [String]
+  property :name, String
 
   belongs_to :wife
 
diff --git a/spec/fixtures/models/kid.rb b/spec/fixtures/models/kid.rb
index bb81baff..bb125870 100644
--- a/spec/fixtures/models/kid.rb
+++ b/spec/fixtures/models/kid.rb
@@ -1,5 +1,5 @@
 class  Kid < CouchRest::Model::Base
-  property :name, [String]
+  property :name, String
 
   belongs_to :dad, :class_name => 'Husband'
   belongs_to :mum, :class_name => 'Wife'
diff --git a/spec/fixtures/models/wife.rb b/spec/fixtures/models/wife.rb
index b24f5f8c..8aa06308 100644
--- a/spec/fixtures/models/wife.rb
+++ b/spec/fixtures/models/wife.rb
@@ -1,5 +1,5 @@
 class  Wife < CouchRest::Model::Base
-  property :name, [String]
+  property :name, String
 
   belongs_to :husband
 

From 0bdf3f12c76ffa062d49c084d00721731b00b8b7 Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Tue, 20 Jan 2015 21:38:29 +0000
Subject: [PATCH 04/21] [back_assignments] make examples 'not implemented yet'

---
 spec/unit/assocations_dual_spec.rb | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index 7d437d79..cb686571 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -5,29 +5,26 @@
 
   describe 'of type belongs_to' do
     context 'the other side also belongs_to (1-1)' do
-      it 'should set the other side property too' do
-      end
+      it 'should set the other side property too'
     end
 
     context 'the other side do not back associate (1-0)' do
-      it 'should set property without error' do
-      end
+      it 'should set property without error'
+
     end
 
     context 'the other side associate as a collection (1-n)' do
-      it 'should be part of the collection weh setting the property' do
-      end
+      it 'should be part of the collection weh setting the property'
     end
   end
 
-  descibe 'of type collection_of' do
+  describe 'of type collection_of' do
     context 'the other side is a belongs_to (n-1)' do
       it 'should populate the belongs_to property when added to the collection'
     end
 
     context 'the other side do not back associate (n-0)' do
-      it 'should set property without error' do
-      end
+      it 'should set property without error'
     end
   end
 end

From e48dd9f7df597f0deb1060add3e4eac135456b3a Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Tue, 20 Jan 2015 21:40:06 +0000
Subject: [PATCH 05/21] [back_assignments] partial try to remember associations

---
 lib/couchrest/model/associations.rb | 18 ++++++++++++++----
 spec/unit/assocations_dual_spec.rb  |  9 ++++++++-
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index 6916069f..9b93cf9a 100644
--- a/lib/couchrest/model/associations.rb
+++ b/lib/couchrest/model/associations.rb
@@ -3,11 +3,13 @@ module Model
     module Associations
 
       # Basic support for relationships between CouchRest::Model::Base
-      
+
       def self.included(base)
         base.extend(ClassMethods)
       end
 
+      Association = Struct.new(:type, :attribute, :options, :target)
+
       module ClassMethods
 
         # Define an association that this object belongs to.
@@ -15,14 +17,14 @@ module ClassMethods
         # An attribute will be created matching the name of the attribute
         # with '_id' on the end, or the foreign key (:foreign_key) provided.
         #
-        # Searching for the assocated object is performed using a string 
+        # Searching for the assocated object is performed using a string
         # (:proxy) to be evaulated in the context of the owner. Typically
         # this will be set to the class name (:class_name), or determined
         # automatically if the owner belongs to a proxy object.
         #
         # If the association owner is proxied by another model, than an attempt will
         # be made to automatically determine the correct place to request
-        # the documents. Typically, this is a method with the pluralized name of the 
+        # the documents. Typically, this is a method with the pluralized name of the
         # association inside owner's owner, or proxy.
         #
         # For example, imagine a company acts as a proxy for invoices and clients.
@@ -32,7 +34,7 @@ module ClassMethods
         #
         #    self.company.clients
         #
-        # If the name of the collection proxy is not the pluralized assocation name, 
+        # If the name of the collection proxy is not the pluralized assocation name,
         # it can be set with the :proxy_name option.
         #
         def belongs_to(attrib, *options)
@@ -40,6 +42,8 @@ def belongs_to(attrib, *options)
 
           property(opts[:foreign_key], String, opts)
 
+          associations.push(Association.new(:belongs_to, attrib, options, nil))
+
           create_association_property_setter(attrib, opts)
           create_belongs_to_getter(attrib, opts)
           create_belongs_to_setter(attrib, opts)
@@ -91,6 +95,8 @@ def collection_of(attrib, *options)
 
           property(opts[:foreign_key], [String], opts)
 
+          associations.push(Association.new(:belongs_to, attrib, options, nil))
+
           create_association_property_setter(attrib, opts)
           create_collection_of_getter(attrib, opts)
           create_collection_of_setter(attrib, opts)
@@ -99,6 +105,10 @@ def collection_of(attrib, *options)
 
         private
 
+        def associations
+          @_associations ||= []
+        end
+
         def merge_belongs_to_association_options(attrib, options = nil)
           opts = {
             :foreign_key => attrib.to_s.singularize + '_id',
diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index cb686571..02a3b9fc 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -3,9 +3,16 @@
 
 describe 'Associations' do
 
+  let(:father) { Husband.create(name: 'bob')}
+  let(:mummy)  { Wife.create(   name: 'claire')}
+  let(:kid)    { Kid.create(    name: 'Vladimir')}
+
   describe 'of type belongs_to' do
     context 'the other side also belongs_to (1-1)' do
-      it 'should set the other side property too'
+      it 'should set the other side property too' do
+        father.wife = mummy
+        expect(mummy.husband).to eq(father)
+      end
     end
 
     context 'the other side do not back associate (1-0)' do

From 6c8d3aead004b4f3e140ab66bfdc37aa54c2ec71 Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Tue, 20 Jan 2015 23:35:53 +0000
Subject: [PATCH 06/21] [back_assignments] belongs_to (1-1) back asignment
 works

---
 lib/couchrest/model/associations.rb | 14 ++++++++++----
 spec/unit/assocations_dual_spec.rb  |  2 +-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index 9b93cf9a..2676aa6b 100644
--- a/lib/couchrest/model/associations.rb
+++ b/lib/couchrest/model/associations.rb
@@ -42,7 +42,7 @@ def belongs_to(attrib, *options)
 
           property(opts[:foreign_key], String, opts)
 
-          associations.push(Association.new(:belongs_to, attrib, options, nil))
+          associations.push(Association.new(:belongs_to, attrib, opts, nil))
 
           create_association_property_setter(attrib, opts)
           create_belongs_to_getter(attrib, opts)
@@ -95,7 +95,7 @@ def collection_of(attrib, *options)
 
           property(opts[:foreign_key], [String], opts)
 
-          associations.push(Association.new(:belongs_to, attrib, options, nil))
+          associations.push(Association.new(:belongs_to, attrib, opts, nil))
 
           create_association_property_setter(attrib, opts)
           create_collection_of_getter(attrib, opts)
@@ -103,12 +103,12 @@ def collection_of(attrib, *options)
         end
 
 
-        private
-
         def associations
           @_associations ||= []
         end
 
+        private
+
         def merge_belongs_to_association_options(attrib, options = nil)
           opts = {
             :foreign_key => attrib.to_s.singularize + '_id',
@@ -157,6 +157,7 @@ def create_belongs_to_setter(attrib, options)
           class_eval <<-EOS, __FILE__, __LINE__ + 1
             def #{attrib}=(value)
               self.#{options[:foreign_key]} = value.nil? ? nil : value.id
+              value.set_back_association(self, #{options})
               @#{attrib} = value
             end
           EOS
@@ -184,6 +185,11 @@ def #{attrib}=(value)
 
       end
 
+      def set_back_association(value, options)
+        assoc = self.class.associations.detect { |assoc| assoc[:options][:class_name] == value.class.name }
+        send("#{assoc[:options][:foreign_key]}=", (value.nil? ? nil : value.id))
+      end
+
     end
 
     # Special proxy for a collection of items so that adding and removing
diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index 02a3b9fc..b3804367 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -11,7 +11,7 @@
     context 'the other side also belongs_to (1-1)' do
       it 'should set the other side property too' do
         father.wife = mummy
-        expect(mummy.husband).to eq(father)
+        mummy.husband.should eql(father)
       end
     end
 

From 1df987d13084172f2839148c890a90cc4160f263 Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Thu, 22 Jan 2015 21:37:51 +0000
Subject: [PATCH 07/21] [back_assignments] from belongs_to done

---
 lib/couchrest/model/associations.rb | 12 +++++++++---
 spec/unit/assocations_dual_spec.rb  | 11 +++++++++--
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index 2676aa6b..4420e899 100644
--- a/lib/couchrest/model/associations.rb
+++ b/lib/couchrest/model/associations.rb
@@ -95,7 +95,7 @@ def collection_of(attrib, *options)
 
           property(opts[:foreign_key], [String], opts)
 
-          associations.push(Association.new(:belongs_to, attrib, opts, nil))
+          associations.push(Association.new(:collection_of, attrib, opts, nil))
 
           create_association_property_setter(attrib, opts)
           create_collection_of_getter(attrib, opts)
@@ -186,8 +186,14 @@ def #{attrib}=(value)
       end
 
       def set_back_association(value, options)
-        assoc = self.class.associations.detect { |assoc| assoc[:options][:class_name] == value.class.name }
-        send("#{assoc[:options][:foreign_key]}=", (value.nil? ? nil : value.id))
+        assoc = self.class.associations.detect { |ass| ass[:options][:class_name] == value.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
diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index b3804367..b0c621fb 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -16,12 +16,19 @@
     end
 
     context 'the other side do not back associate (1-0)' do
-      it 'should set property without error'
+      let(:invoice) { SaleInvoice.create(:price => 2000) }
+      let(:client)  { Client.create(:name => "Sam Lown") }
+      it 'should set property without error' do
+        lambda { invoice.client = client }.should_not raise_error
+      end
 
     end
 
     context 'the other side associate as a collection (1-n)' do
-      it 'should be part of the collection weh setting the property'
+      it 'should be part of the collection when setting the property' do
+        kid.dad = father
+        father.children.should include(kid)
+      end
     end
   end
 

From 83ab20843e3b9075723d00295cb44f0597dee82e Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Sat, 24 Jan 2015 00:14:27 +0000
Subject: [PATCH 08/21] [back_assignments] - unset belongs_to when setting
 origin to nil - set/unset collection_of

---
 lib/couchrest/model/associations.rb | 21 +++++--
 spec/unit/assocations_dual_spec.rb  | 95 +++++++++++++++++++++++++++--
 2 files changed, 108 insertions(+), 8 deletions(-)

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index 4420e899..c59ef0b0 100644
--- a/lib/couchrest/model/associations.rb
+++ b/lib/couchrest/model/associations.rb
@@ -156,8 +156,13 @@ def #{attrib}
         def create_belongs_to_setter(attrib, options)
           class_eval <<-EOS, __FILE__, __LINE__ + 1
             def #{attrib}=(value)
-              self.#{options[:foreign_key]} = value.nil? ? nil : value.id
-              value.set_back_association(self, #{options})
+                old_binding = @#{attrib}
+                self.#{options[:foreign_key]} = value.nil? ? nil : value.id
+              unless value.nil?
+                value.set_back_association(self, self.class.name)
+              else
+                old_binding.set_back_association(nil, self.class.name)
+              end
               @#{attrib} = value
             end
           EOS
@@ -185,8 +190,8 @@ def #{attrib}=(value)
 
       end
 
-      def set_back_association(value, options)
-        assoc = self.class.associations.detect { |ass| ass[:options][:class_name] == value.class.name }
+      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
@@ -215,34 +220,42 @@ def initialize(array, property, parent)
       def << obj
         check_obj(obj)
         casted_by[casted_by_property.to_s] << obj.id
+        obj.set_back_association(casted_by, casted_by.class.name)
         super(obj)
       end
 
       def push(obj)
         check_obj(obj)
         casted_by[casted_by_property.to_s].push obj.id
+        obj.set_back_association(casted_by, casted_by.class.name)
         super(obj)
       end
 
       def unshift(obj)
         check_obj(obj)
         casted_by[casted_by_property.to_s].unshift obj.id
+        obj.set_back_association(casted_by, casted_by.class.name)
         super(obj)
       end
 
       def []= index, obj
         check_obj(obj)
         casted_by[casted_by_property.to_s][index] = obj.id
+        obj.set_back_association(casted_by, casted_by.class.name)
         super(index, obj)
       end
 
       def pop
+        obj = casted_by.send(casted_by_property.options[:proxy_name]).last
         casted_by[casted_by_property.to_s].pop
+        obj.set_back_association(nil, casted_by.class.name)
         super
       end
 
       def shift
+        obj = casted_by.send(casted_by_property.options[:proxy_name]).first
         casted_by[casted_by_property.to_s].shift
+        obj.set_back_association(nil, casted_by.class.name)
         super
       end
 
diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index b0c621fb..ba2ac095 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -33,12 +33,99 @@
   end
 
   describe 'of type collection_of' do
-    context 'the other side is a belongs_to (n-1)' do
-      it 'should populate the belongs_to property when added to the collection'
+    context 'with the other side is a belongs_to (n-1).' do
+      context 'Adding to the collection using <<' do
+        it 'should populate the belongs_to property' do
+          father.children << kid
+          kid.dad.should eq(father)
+        end
+      end
+
+      context 'Adding to the collection using push' do
+        it 'should populate the belongs_to property' do
+          father.children.push kid
+          kid.dad.should eq(father)
+        end
+      end
+
+      context 'Adding to the collection using unshift' do
+        it 'should populate the belongs_to property' do
+          father.children.unshift kid
+          kid.dad.should eq(father)
+        end
+      end
+
+      context 'Adding to the collection using [n]=' do
+        it 'should populate the belongs_to property' do
+          father.children[3]= kid
+          kid.dad.should eq(father)
+        end
+      end
+
+      context 'removing from the collection using pop' do
+        it 'should set nil the belongs_to property' do
+          father.children.push kid
+          father.children.pop
+          kid.dad.should be_nil
+        end
+      end
+
+      context 'removing from the collection using shift' do
+        it 'should set nil the belongs_to property' do
+          father.children.push kid
+          father.children.shift
+          kid.dad.should be_nil
+        end
+      end
+
     end
 
-    context 'the other side do not back associate (n-0)' do
-      it 'should set property without error'
+    context 'with the other side do not back associate (n-0)' do
+      let(:invoice) { SaleInvoice.create(:price => 2000) }
+      let(:entry)  { SaleEntry.create(:description => 'test line 1', :price => 500) }
+
+      context 'Adding to the collection using <<' do
+        it 'should set property without error' do
+          lambda { invoice.entries << entry}.should_not raise_error
+        end
+      end
+
+      context 'Adding to the collection using push' do
+        it 'should set property without error' do
+          lambda { invoice.entries.push entry}.should_not raise_error
+        end
+
+      context 'Adding to the collection using unshift' do
+        it 'should set property without error' do
+          lambda { invoice.entries.unshift entry}.should_not raise_error
+        end
+      end
+
+      context 'Adding to the collection using []=' do
+        it 'should set property without error' do
+          lambda { invoice.entries[3]= entry}.should_not raise_error
+        end
+      end
+
+      context 'removing from the collection using pop' do
+        it 'should set nil the belongs_to property' do
+          invoice.entries.push entry
+          lambda { invoice.entries.pop }.should_not raise_error
+        end
+      end
+
+      context 'removing from the collection using shift' do
+        it 'should set nil the belongs_to property' do
+          invoice.entries.push entry
+          lambda { invoice.entries.shift }.should_not raise_error
+        end
+      end
+
+      end
     end
   end
+
+  describe 'when object is saved' do
+    it 'should also save other side'
+  end
 end

From 8f0635598f7e1f5ccca7ad4b2bdb8920585f8eb2 Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Sun, 25 Jan 2015 22:54:39 +0000
Subject: [PATCH 09/21] [back_assignments] remove belongs_to other side when
 setting 1-1 assoc to nil

---
 spec/unit/assocations_dual_spec.rb | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index ba2ac095..9e46d589 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -8,14 +8,20 @@
   let(:kid)    { Kid.create(    name: 'Vladimir')}
 
   describe 'of type belongs_to' do
-    context 'the other side also belongs_to (1-1)' 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)
       end
+
+      it 'should remove the other side if value is nil' do
+        father.wife = mummy
+        father.wife = nil
+        mummy.husband.should be_nil
+      end
     end
 
-    context 'the other side do not back associate (1-0)' do
+    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
@@ -24,7 +30,7 @@
 
     end
 
-    context 'the other side associate as a collection (1-n)' do
+    context 'with the other side associate as a collection (1-n)' do
       it 'should be part of the collection when setting the property' do
         kid.dad = father
         father.children.should include(kid)

From 98f7fedb910369acf2a35bc8a7765d2e84dc132b Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Sun, 25 Jan 2015 22:55:26 +0000
Subject: [PATCH 10/21] [back_assignments] put callbacks before association
 when including in model.base.rb to be able to define a after_save for dirty
 associations.

---
 lib/couchrest/model/base.rb | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/lib/couchrest/model/base.rb b/lib/couchrest/model/base.rb
index d6acfd2c..ae0a7387 100644
--- a/lib/couchrest/model/base.rb
+++ b/lib/couchrest/model/base.rb
@@ -13,13 +13,13 @@ class Base < CouchRest::Document
       include ExtendedAttachments
       include Proxyable
       include PropertyProtection
-      include Associations
       include Validations
       include Callbacks
+      include Associations
       include Designs
       include CastedBy
       include Dirty
-      
+
 
       def self.subclasses
         @subclasses ||= []
@@ -68,13 +68,13 @@ def initialize(attributes = {}, options = {})
       alias :new_record? :new?
       alias :new_document? :new?
 
-      # Compare this model with another by confirming to see 
+      # Compare this model with another by confirming to see
       # if the IDs and their databases match!
       #
-      # Camparison of the database is required in case the 
+      # Camparison of the database is required in case the
       # model has been proxied or loaded elsewhere.
       #
-      # A Basic CouchRest document will only ever compare using 
+      # A Basic CouchRest document will only ever compare using
       # a Hash comparison on the attributes.
       def == other
         return false unless other.is_a?(Base)

From 4cd377d899418d08d5e4afc5eee68b9db64f3c8a Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Sun, 25 Jan 2015 23:40:46 +0000
Subject: [PATCH 11/21] [back_assignments] propagate save for 1-1 associations

---
 lib/couchrest/model/associations.rb | 27 ++++++++++++++++++++++-----
 spec/unit/assocations_dual_spec.rb  | 12 +++++++++---
 2 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index c59ef0b0..b177739a 100644
--- a/lib/couchrest/model/associations.rb
+++ b/lib/couchrest/model/associations.rb
@@ -1,11 +1,12 @@
 module CouchRest
   module Model
     module Associations
+      extend ActiveSupport::Concern
 
       # Basic support for relationships between CouchRest::Model::Base
 
-      def self.included(base)
-        base.extend(ClassMethods)
+      included do
+        after_save :save_dirty_association if respond_to?(:after_save)
       end
 
       Association = Struct.new(:type, :attribute, :options, :target)
@@ -156,13 +157,15 @@ def #{attrib}
         def create_belongs_to_setter(attrib, options)
           class_eval <<-EOS, __FILE__, __LINE__ + 1
             def #{attrib}=(value)
-                old_binding = @#{attrib}
+                binding = @#{attrib}
                 self.#{options[:foreign_key]} = value.nil? ? nil : value.id
               unless value.nil?
-                value.set_back_association(self, self.class.name)
+                binding = value
+                binding.set_back_association(self, self.class.name)
               else
-                old_binding.set_back_association(nil, self.class.name)
+                binding.set_back_association(nil, self.class.name)
               end
+              register_dirty_association(binding)
               @#{attrib} = value
             end
           EOS
@@ -201,6 +204,20 @@ def set_back_association(value, class_name)
         end
       end
 
+      def dirty_associations
+        @_dirty_associations ||= []
+      end
+
+      def register_dirty_association(obj)
+        dirty_associations << obj unless @_dirty_associations.include?(obj)
+      end
+
+      def save_dirty_association
+        dirty_associations.each do |obj|
+          obj.save
+        end
+      end
+
     end
 
     # Special proxy for a collection of items so that adding and removing
diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index 9e46d589..932c1f12 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -36,6 +36,15 @@
         father.children.should include(kid)
       end
     end
+
+    describe 'when object is saved' do
+      it 'should also save other side' do
+        father.wife = mummy
+        mummy.should_receive(:save)
+        father.save
+      end
+  end
+
   end
 
   describe 'of type collection_of' do
@@ -131,7 +140,4 @@
     end
   end
 
-  describe 'when object is saved' do
-    it 'should also save other side'
-  end
 end

From 330c1b87951d25f6813cdf5b9747830ea71093ad Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Mon, 26 Jan 2015 23:13:32 +0000
Subject: [PATCH 12/21] [back_assignments] - do not call save more than once -
 propagate save for collection_of associations

---
 lib/couchrest/model/associations.rb |  9 ++-
 spec/unit/assocations_dual_spec.rb  | 92 ++++++++++++++++++++++-------
 2 files changed, 80 insertions(+), 21 deletions(-)

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index b177739a..ef433513 100644
--- a/lib/couchrest/model/associations.rb
+++ b/lib/couchrest/model/associations.rb
@@ -213,7 +213,8 @@ def register_dirty_association(obj)
       end
 
       def save_dirty_association
-        dirty_associations.each do |obj|
+        while !dirty_associations.empty? do
+          obj = dirty_associations.pop
           obj.save
         end
       end
@@ -238,6 +239,7 @@ def << obj
         check_obj(obj)
         casted_by[casted_by_property.to_s] << obj.id
         obj.set_back_association(casted_by, casted_by.class.name)
+        casted_by.register_dirty_association(obj)
         super(obj)
       end
 
@@ -245,6 +247,7 @@ def push(obj)
         check_obj(obj)
         casted_by[casted_by_property.to_s].push obj.id
         obj.set_back_association(casted_by, casted_by.class.name)
+        casted_by.register_dirty_association(obj)
         super(obj)
       end
 
@@ -252,6 +255,7 @@ def unshift(obj)
         check_obj(obj)
         casted_by[casted_by_property.to_s].unshift obj.id
         obj.set_back_association(casted_by, casted_by.class.name)
+        casted_by.register_dirty_association(obj)
         super(obj)
       end
 
@@ -259,6 +263,7 @@ def []= index, obj
         check_obj(obj)
         casted_by[casted_by_property.to_s][index] = obj.id
         obj.set_back_association(casted_by, casted_by.class.name)
+        casted_by.register_dirty_association(obj)
         super(index, obj)
       end
 
@@ -266,6 +271,7 @@ def pop
         obj = casted_by.send(casted_by_property.options[:proxy_name]).last
         casted_by[casted_by_property.to_s].pop
         obj.set_back_association(nil, casted_by.class.name)
+        casted_by.register_dirty_association(obj)
         super
       end
 
@@ -273,6 +279,7 @@ def shift
         obj = casted_by.send(casted_by_property.options[:proxy_name]).first
         casted_by[casted_by_property.to_s].shift
         obj.set_back_association(nil, casted_by.class.name)
+        casted_by.register_dirty_association(obj)
         super
       end
 
diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index 932c1f12..cae97339 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -43,8 +43,14 @@
         mummy.should_receive(:save)
         father.save
       end
-  end
-
+      it 'should not call save twice in a row' do
+        father.wife = mummy
+        mummy.should_receive(:save).exactly(1)
+        father.save
+        father.name = 'rogers'
+        father.save
+      end
+    end
   end
 
   describe 'of type collection_of' do
@@ -54,6 +60,13 @@
           father.children << kid
           kid.dad.should eq(father)
         end
+        describe 'when object is saved' do
+          it 'should also save other side' do
+            father.children << kid
+            kid.should_receive(:save)
+            father.save
+          end
+        end
       end
 
       context 'Adding to the collection using push' do
@@ -61,6 +74,13 @@
           father.children.push kid
           kid.dad.should eq(father)
         end
+        describe 'when object is saved' do
+          it 'should also save other side' do
+            father.children.push kid
+            kid.should_receive(:save)
+            father.save
+          end
+        end
       end
 
       context 'Adding to the collection using unshift' do
@@ -68,6 +88,13 @@
           father.children.unshift kid
           kid.dad.should eq(father)
         end
+        describe 'when object is saved' do
+          it 'should also save other side' do
+            father.children.unshift kid
+            kid.should_receive(:save)
+            father.save
+          end
+        end
       end
 
       context 'Adding to the collection using [n]=' do
@@ -75,6 +102,13 @@
           father.children[3]= kid
           kid.dad.should eq(father)
         end
+        describe 'when object is saved' do
+          it 'should also save other side' do
+            father.children[4] = kid
+            kid.should_receive(:save)
+            father.save
+          end
+        end
       end
 
       context 'removing from the collection using pop' do
@@ -83,6 +117,15 @@
           father.children.pop
           kid.dad.should be_nil
         end
+        describe 'when object is saved' do
+          it 'should also save other side' do
+            father.children.push kid
+            father.save
+            father.children.pop
+            kid.should_receive(:save)
+            father.save
+          end
+        end
       end
 
       context 'removing from the collection using shift' do
@@ -91,6 +134,15 @@
           father.children.shift
           kid.dad.should be_nil
         end
+        describe 'when object is saved' do
+          it 'should also save other side' do
+            father.children.push kid
+            father.save
+            father.children.shift
+            kid.should_receive(:save)
+            father.save
+          end
+        end
       end
 
     end
@@ -110,31 +162,31 @@
           lambda { invoice.entries.push entry}.should_not raise_error
         end
 
-      context 'Adding to the collection using unshift' do
-        it 'should set property without error' do
-          lambda { invoice.entries.unshift entry}.should_not raise_error
+        context 'Adding to the collection using unshift' do
+          it 'should set property without error' do
+            lambda { invoice.entries.unshift entry}.should_not raise_error
+          end
         end
-      end
 
-      context 'Adding to the collection using []=' do
-        it 'should set property without error' do
-          lambda { invoice.entries[3]= entry}.should_not raise_error
+        context 'Adding to the collection using []=' do
+          it 'should set property without error' do
+            lambda { invoice.entries[3]= entry}.should_not raise_error
+          end
         end
-      end
 
-      context 'removing from the collection using pop' do
-        it 'should set nil the belongs_to property' do
-          invoice.entries.push entry
-          lambda { invoice.entries.pop }.should_not raise_error
+        context 'removing from the collection using pop' do
+          it 'should set nil the belongs_to property' do
+            invoice.entries.push entry
+            lambda { invoice.entries.pop }.should_not raise_error
+          end
         end
-      end
 
-      context 'removing from the collection using shift' do
-        it 'should set nil the belongs_to property' do
-          invoice.entries.push entry
-          lambda { invoice.entries.shift }.should_not raise_error
+        context 'removing from the collection using shift' do
+          it 'should set nil the belongs_to property' do
+            invoice.entries.push entry
+            lambda { invoice.entries.shift }.should_not raise_error
+          end
         end
-      end
 
       end
     end

From b97403b8ead703fc06c6c1e2ec20d72110ede0ae Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Wed, 11 Mar 2015 23:07:29 +0000
Subject: [PATCH 13/21] add option to support specifying reverse association
 field

---
 lib/couchrest/model/associations.rb | 33 +++++++++++++++++++----------
 spec/fixtures/models/husband.rb     |  7 ------
 spec/fixtures/models/kid.rb         |  4 ++--
 spec/fixtures/models/parent.rb      | 10 +++++++++
 spec/fixtures/models/super_power.rb |  5 +++++
 spec/fixtures/models/wife.rb        |  7 ------
 spec/unit/assocations_dual_spec.rb  | 30 ++++++++++++++++++--------
 7 files changed, 60 insertions(+), 36 deletions(-)
 delete mode 100644 spec/fixtures/models/husband.rb
 create mode 100644 spec/fixtures/models/parent.rb
 create mode 100644 spec/fixtures/models/super_power.rb
 delete mode 100644 spec/fixtures/models/wife.rb

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index ef433513..88227810 100644
--- a/lib/couchrest/model/associations.rb
+++ b/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
 
diff --git a/spec/fixtures/models/husband.rb b/spec/fixtures/models/husband.rb
deleted file mode 100644
index 291e33bc..00000000
--- a/spec/fixtures/models/husband.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-class  Husband < CouchRest::Model::Base
-  property :name, String
-
-  belongs_to :wife
-
-  collection_of :children, :class_name => 'Kid'
-end
diff --git a/spec/fixtures/models/kid.rb b/spec/fixtures/models/kid.rb
index bb125870..518ef2d5 100644
--- a/spec/fixtures/models/kid.rb
+++ b/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
diff --git a/spec/fixtures/models/parent.rb b/spec/fixtures/models/parent.rb
new file mode 100644
index 00000000..7820c117
--- /dev/null
+++ b/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
diff --git a/spec/fixtures/models/super_power.rb b/spec/fixtures/models/super_power.rb
new file mode 100644
index 00000000..3dc58449
--- /dev/null
+++ b/spec/fixtures/models/super_power.rb
@@ -0,0 +1,5 @@
+class SuperPower < CouchRest::Model::Base
+  property :description, String
+
+  belongs_to :parent
+end
diff --git a/spec/fixtures/models/wife.rb b/spec/fixtures/models/wife.rb
deleted file mode 100644
index 8aa06308..00000000
--- a/spec/fixtures/models/wife.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-class  Wife < CouchRest::Model::Base
-  property :name, String
-
-  belongs_to :husband
-
-  collection_of :children, :class_name => 'Kid'
-end
diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index cae97339..88c12750 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -3,21 +3,32 @@
 
 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
 
@@ -25,6 +36,7 @@
       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
 

From 1fc6cf70b38475e8a9aaa73a21c847b4ae8812ef Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Wed, 11 Mar 2015 23:07:29 +0000
Subject: [PATCH 14/21] [back_assignments] add option to support specifying
 reverse association field

---
 lib/couchrest/model/associations.rb | 33 +++++++++++++++++++----------
 spec/fixtures/models/husband.rb     |  7 ------
 spec/fixtures/models/kid.rb         |  4 ++--
 spec/fixtures/models/parent.rb      | 10 +++++++++
 spec/fixtures/models/super_power.rb |  5 +++++
 spec/fixtures/models/wife.rb        |  7 ------
 spec/unit/assocations_dual_spec.rb  | 30 ++++++++++++++++++--------
 7 files changed, 60 insertions(+), 36 deletions(-)
 delete mode 100644 spec/fixtures/models/husband.rb
 create mode 100644 spec/fixtures/models/parent.rb
 create mode 100644 spec/fixtures/models/super_power.rb
 delete mode 100644 spec/fixtures/models/wife.rb

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index ef433513..88227810 100644
--- a/lib/couchrest/model/associations.rb
+++ b/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
 
diff --git a/spec/fixtures/models/husband.rb b/spec/fixtures/models/husband.rb
deleted file mode 100644
index 291e33bc..00000000
--- a/spec/fixtures/models/husband.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-class  Husband < CouchRest::Model::Base
-  property :name, String
-
-  belongs_to :wife
-
-  collection_of :children, :class_name => 'Kid'
-end
diff --git a/spec/fixtures/models/kid.rb b/spec/fixtures/models/kid.rb
index bb125870..518ef2d5 100644
--- a/spec/fixtures/models/kid.rb
+++ b/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
diff --git a/spec/fixtures/models/parent.rb b/spec/fixtures/models/parent.rb
new file mode 100644
index 00000000..7820c117
--- /dev/null
+++ b/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
diff --git a/spec/fixtures/models/super_power.rb b/spec/fixtures/models/super_power.rb
new file mode 100644
index 00000000..3dc58449
--- /dev/null
+++ b/spec/fixtures/models/super_power.rb
@@ -0,0 +1,5 @@
+class SuperPower < CouchRest::Model::Base
+  property :description, String
+
+  belongs_to :parent
+end
diff --git a/spec/fixtures/models/wife.rb b/spec/fixtures/models/wife.rb
deleted file mode 100644
index 8aa06308..00000000
--- a/spec/fixtures/models/wife.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-class  Wife < CouchRest::Model::Base
-  property :name, String
-
-  belongs_to :husband
-
-  collection_of :children, :class_name => 'Kid'
-end
diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index cae97339..88c12750 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -3,21 +3,32 @@
 
 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
 
@@ -25,6 +36,7 @@
       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
 

From 9d54af6b2fb5ab171e6c6c7acd27c12e3bbceb12 Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Fri, 13 Mar 2015 20:34:02 +0000
Subject: [PATCH 15/21] [back_assignments] add reverse_association on
 collections

---
 lib/couchrest/model/associations.rb | 33 +++++++++++-------------
 spec/fixtures/models/parent.rb      |  1 +
 spec/unit/assocations_dual_spec.rb  | 39 +++++++++++++++++++++++++++--
 3 files changed, 53 insertions(+), 20 deletions(-)

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index 88227810..45efead4 100644
--- a/lib/couchrest/model/associations.rb
+++ b/lib/couchrest/model/associations.rb
@@ -247,41 +247,29 @@ def initialize(array, property, parent)
       end
 
       def << obj
-        check_obj(obj)
-        casted_by[casted_by_property.to_s] << obj.id
-        obj.set_back_association(casted_by, casted_by.class.name)
-        casted_by.register_dirty_association(obj)
+        add_to_collection_with(:<<, obj)
         super(obj)
       end
 
       def push(obj)
-        check_obj(obj)
-        casted_by[casted_by_property.to_s].push obj.id
-        obj.set_back_association(casted_by, casted_by.class.name)
-        casted_by.register_dirty_association(obj)
+        add_to_collection_with(:push, obj)
         super(obj)
       end
 
       def unshift(obj)
-        check_obj(obj)
-        casted_by[casted_by_property.to_s].unshift obj.id
-        obj.set_back_association(casted_by, casted_by.class.name)
-        casted_by.register_dirty_association(obj)
+        add_to_collection_with(:unshift, obj)
         super(obj)
       end
 
       def []= index, obj
-        check_obj(obj)
-        casted_by[casted_by_property.to_s][index] = obj.id
-        obj.set_back_association(casted_by, casted_by.class.name)
-        casted_by.register_dirty_association(obj)
+        add_to_collection_with(:[]=, obj, index)
         super(index, obj)
       end
 
       def pop
         obj = casted_by.send(casted_by_property.options[:proxy_name]).last
         casted_by[casted_by_property.to_s].pop
-        obj.set_back_association(nil, casted_by.class.name)
+        obj.set_back_association(nil, casted_by.class.name, casted_by_property.options[:reverse_association])
         casted_by.register_dirty_association(obj)
         super
       end
@@ -289,7 +277,7 @@ def pop
       def shift
         obj = casted_by.send(casted_by_property.options[:proxy_name]).first
         casted_by[casted_by_property.to_s].shift
-        obj.set_back_association(nil, casted_by.class.name)
+        obj.set_back_association(nil, casted_by.class.name, casted_by_property.options[:reverse_association])
         casted_by.register_dirty_association(obj)
         super
       end
@@ -300,6 +288,15 @@ def check_obj(obj)
         raise "Object cannot be added to #{casted_by.class.to_s}##{casted_by_property.to_s} collection unless saved" if obj.new?
       end
 
+      def add_to_collection_with(method, obj, index=nil)
+        check_obj(obj)
+        args = [ obj.id ]
+        args = args.insert(0, index) if index
+        casted_by[casted_by_property.to_s].send(method, *args)
+        obj.set_back_association(casted_by, casted_by.class.name, casted_by_property.options[:reverse_association])
+        casted_by.register_dirty_association(obj)
+      end
+
       # Override CastedArray instantiation_and_cast method for a simpler
       # version that will not try to cast the model.
       def instantiate_and_cast(obj, change = true)
diff --git a/spec/fixtures/models/parent.rb b/spec/fixtures/models/parent.rb
index 7820c117..ee1418f5 100644
--- a/spec/fixtures/models/parent.rb
+++ b/spec/fixtures/models/parent.rb
@@ -7,4 +7,5 @@ class  Parent < CouchRest::Model::Base
   belongs_to :lives_with, :class_name => :parent, :reverse_association => :lives_with
 
   collection_of :children, :class_name => 'Kid'
+  collection_of :pets , :reverse_association => :owner
 end
diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index 88c12750..89657f79 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -5,8 +5,9 @@
 
   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')}
+  let(:mummy)  { Parent.create(name: 'Claire')}
+  let(:kid)    { Kid.create(   name: 'Vladimir')}
+  let(:dog)    { Pet.create(   name: 'Valdo' )}
 
   describe 'of type belongs_to' do
     context 'with the other side also belongs_to (1-1)' do
@@ -72,6 +73,12 @@
           father.children << kid
           kid.dad.should eq(father)
         end
+        context 'when reverse_association is specified' do
+          it 'should populate the belongs_to property' do
+            father.pets << dog
+            dog.owner.should eq(father)
+          end
+        end
         describe 'when object is saved' do
           it 'should also save other side' do
             father.children << kid
@@ -86,6 +93,12 @@
           father.children.push kid
           kid.dad.should eq(father)
         end
+        context 'when reverse_association is specified' do
+          it 'should populate the belongs_to property' do
+            father.pets.push dog
+            dog.owner.should eq(father)
+          end
+        end
         describe 'when object is saved' do
           it 'should also save other side' do
             father.children.push kid
@@ -100,6 +113,10 @@
           father.children.unshift kid
           kid.dad.should eq(father)
         end
+        it 'should populate the belongs_to property' do
+          father.pets.unshift dog
+          dog.owner.should eq(father)
+        end
         describe 'when object is saved' do
           it 'should also save other side' do
             father.children.unshift kid
@@ -114,6 +131,10 @@
           father.children[3]= kid
           kid.dad.should eq(father)
         end
+        it 'should populate the belongs_to property' do
+          father.pets[3] = dog
+          dog.owner.should eq(father)
+        end
         describe 'when object is saved' do
           it 'should also save other side' do
             father.children[4] = kid
@@ -129,6 +150,13 @@
           father.children.pop
           kid.dad.should be_nil
         end
+        context 'specifying reverse association' do
+          it 'should set nil the belongs_to property' do
+            father.pets.push dog
+            father.pets.pop
+            dog.owner.should be_nil
+          end
+        end
         describe 'when object is saved' do
           it 'should also save other side' do
             father.children.push kid
@@ -146,6 +174,13 @@
           father.children.shift
           kid.dad.should be_nil
         end
+        context 'specifying reverse association' do
+          it 'should set nil the belongs_to property' do
+            father.pets.push dog
+            father.pets.shift
+            dog.owner.should be_nil
+          end
+        end
         describe 'when object is saved' do
           it 'should also save other side' do
             father.children.push kid

From a1d431cf88480b303c8e64439a0d6daf0dff1c20 Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Fri, 13 Mar 2015 22:46:02 +0000
Subject: [PATCH 16/21] [back_assignments] move CollectionOfProxy class in its
 own file

---
 lib/couchrest/model/associations.rb           | 80 +-----------------
 .../model/associations/collection_of_proxy.rb | 81 +++++++++++++++++++
 lib/couchrest_model.rb                        |  1 +
 spec/unit/assocations_spec.rb                 |  2 +-
 4 files changed, 85 insertions(+), 79 deletions(-)
 create mode 100644 lib/couchrest/model/associations/collection_of_proxy.rb

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index 45efead4..02a7885c 100644
--- a/lib/couchrest/model/associations.rb
+++ b/lib/couchrest/model/associations.rb
@@ -180,7 +180,7 @@ def create_collection_of_getter(attrib, options)
             def #{attrib}(reload = false)
               return @#{attrib} unless @#{attrib}.nil? or reload
               ary = self.#{options[:foreign_key]}.collect{|i| #{options[:proxy]}.get(i)}
-              @#{attrib} = ::CouchRest::Model::CollectionOfProxy.new(ary, find_property('#{options[:foreign_key]}'), self)
+              @#{attrib} = ::CouchRest::Model::Associations::CollectionOfProxy.new(ary, find_property('#{options[:foreign_key]}'), self)
             end
           EOS
         end
@@ -188,7 +188,7 @@ def #{attrib}(reload = false)
         def create_collection_of_setter(attrib, options)
           class_eval <<-EOS, __FILE__, __LINE__ + 1
             def #{attrib}=(value)
-              @#{attrib} = ::CouchRest::Model::CollectionOfProxy.new(value, find_property('#{options[:foreign_key]}'), self)
+              @#{attrib} = ::CouchRest::Model::Associations::CollectionOfProxy.new(value, find_property('#{options[:foreign_key]}'), self)
             end
           EOS
         end
@@ -232,82 +232,6 @@ def save_dirty_association
 
     end
 
-    # Special proxy for a collection of items so that adding and removing
-    # to the list automatically updates the associated property.
-    class CollectionOfProxy < CastedArray
-
-      def initialize(array, property, parent)
-        (array ||= []).compact!
-        super(array, property, parent)
-        casted_by[casted_by_property.to_s] = [] # replace the original array!
-        array.compact.each do |obj|
-          check_obj(obj)
-          casted_by[casted_by_property.to_s] << obj.id
-        end
-      end
-
-      def << obj
-        add_to_collection_with(:<<, obj)
-        super(obj)
-      end
-
-      def push(obj)
-        add_to_collection_with(:push, obj)
-        super(obj)
-      end
-
-      def unshift(obj)
-        add_to_collection_with(:unshift, obj)
-        super(obj)
-      end
-
-      def []= index, obj
-        add_to_collection_with(:[]=, obj, index)
-        super(index, obj)
-      end
-
-      def pop
-        obj = casted_by.send(casted_by_property.options[:proxy_name]).last
-        casted_by[casted_by_property.to_s].pop
-        obj.set_back_association(nil, casted_by.class.name, casted_by_property.options[:reverse_association])
-        casted_by.register_dirty_association(obj)
-        super
-      end
-
-      def shift
-        obj = casted_by.send(casted_by_property.options[:proxy_name]).first
-        casted_by[casted_by_property.to_s].shift
-        obj.set_back_association(nil, casted_by.class.name, casted_by_property.options[:reverse_association])
-        casted_by.register_dirty_association(obj)
-        super
-      end
-
-      protected
-
-      def check_obj(obj)
-        raise "Object cannot be added to #{casted_by.class.to_s}##{casted_by_property.to_s} collection unless saved" if obj.new?
-      end
-
-      def add_to_collection_with(method, obj, index=nil)
-        check_obj(obj)
-        args = [ obj.id ]
-        args = args.insert(0, index) if index
-        casted_by[casted_by_property.to_s].send(method, *args)
-        obj.set_back_association(casted_by, casted_by.class.name, casted_by_property.options[:reverse_association])
-        casted_by.register_dirty_association(obj)
-      end
-
-      # Override CastedArray instantiation_and_cast method for a simpler
-      # version that will not try to cast the model.
-      def instantiate_and_cast(obj, change = true)
-        couchrest_parent_will_change! if change && use_dirty?
-        obj.casted_by = casted_by if obj.respond_to?(:casted_by)
-        obj.casted_by_property = casted_by_property if obj.respond_to?(:casted_by_property)
-        obj
-      end
-
-    end
-
   end
 
 end
diff --git a/lib/couchrest/model/associations/collection_of_proxy.rb b/lib/couchrest/model/associations/collection_of_proxy.rb
new file mode 100644
index 00000000..0e772359
--- /dev/null
+++ b/lib/couchrest/model/associations/collection_of_proxy.rb
@@ -0,0 +1,81 @@
+module CouchRest
+  module Model
+    module Associations
+      # Special proxy for a collection of items so that adding and removing
+      # to the list automatically updates the associated property.
+      class CollectionOfProxy < CastedArray
+
+        def initialize(array, property, parent)
+          (array ||= []).compact!
+          super(array, property, parent)
+          casted_by[casted_by_property.to_s] = [] # replace the original array!
+          array.compact.each do |obj|
+            check_obj(obj)
+            casted_by[casted_by_property.to_s] << obj.id
+          end
+        end
+
+        def << obj
+          add_to_collection_with(:<<, obj)
+          super(obj)
+        end
+
+        def push(obj)
+          add_to_collection_with(:push, obj)
+          super(obj)
+        end
+
+        def unshift(obj)
+          add_to_collection_with(:unshift, obj)
+          super(obj)
+        end
+
+        def []= index, obj
+          add_to_collection_with(:[]=, obj, index)
+          super(index, obj)
+        end
+
+        def pop
+          obj = casted_by.send(casted_by_property.options[:proxy_name]).last
+          casted_by[casted_by_property.to_s].pop
+          obj.set_back_association(nil, casted_by.class.name, casted_by_property.options[:reverse_association])
+          casted_by.register_dirty_association(obj)
+          super
+        end
+
+        def shift
+          obj = casted_by.send(casted_by_property.options[:proxy_name]).first
+          casted_by[casted_by_property.to_s].shift
+          obj.set_back_association(nil, casted_by.class.name, casted_by_property.options[:reverse_association])
+          casted_by.register_dirty_association(obj)
+          super
+        end
+
+        protected
+
+        def check_obj(obj)
+          raise "Object cannot be added to #{casted_by.class.to_s}##{casted_by_property.to_s} collection unless saved" if obj.new?
+        end
+
+        def add_to_collection_with(method, obj, index=nil)
+          check_obj(obj)
+          args = [ obj.id ]
+          args = args.insert(0, index) if index
+          casted_by[casted_by_property.to_s].send(method, *args)
+          obj.set_back_association(casted_by, casted_by.class.name, casted_by_property.options[:reverse_association])
+          casted_by.register_dirty_association(obj)
+        end
+
+        # Override CastedArray instantiation_and_cast method for a simpler
+        # version that will not try to cast the model.
+        def instantiate_and_cast(obj, change = true)
+          couchrest_parent_will_change! if change && use_dirty?
+          obj.casted_by = casted_by if obj.respond_to?(:casted_by)
+          obj.casted_by_property = casted_by_property if obj.respond_to?(:casted_by_property)
+          obj
+        end
+
+      end
+    end
+  end
+end
diff --git a/lib/couchrest_model.rb b/lib/couchrest_model.rb
index e66078e7..08c32ab3 100644
--- a/lib/couchrest_model.rb
+++ b/lib/couchrest_model.rb
@@ -40,6 +40,7 @@
 require "couchrest/model/extended_attachments"
 require "couchrest/model/proxyable"
 require "couchrest/model/associations"
+require "couchrest/model/associations/collection_of_proxy"
 require "couchrest/model/configuration"
 require "couchrest/model/connection"
 require "couchrest/model/design"
diff --git a/spec/unit/assocations_spec.rb b/spec/unit/assocations_spec.rb
index 2582bf3d..cb2c2eb5 100644
--- a/spec/unit/assocations_spec.rb
+++ b/spec/unit/assocations_spec.rb
@@ -111,7 +111,7 @@ def SaleInvoice.merge_assoc_opts(*args)
     it "should create an associated property and collection proxy" do
       @invoice.respond_to?('entry_ids').should be_true
       @invoice.respond_to?('entry_ids=').should be_true
-      @invoice.entries.class.should eql(::CouchRest::Model::CollectionOfProxy)
+      @invoice.entries.class.should eql(::CouchRest::Model::Associations::CollectionOfProxy)
     end
 
     it "should allow replacement of objects" do

From 12b54bea847c1a3c6b6631e342cdb9334e86ed6d Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Fri, 13 Mar 2015 22:47:53 +0000
Subject: [PATCH 17/21] [back_assignments] add pet fixctures model

---
 spec/fixtures/models/pet.rb | 6 ++++++
 1 file changed, 6 insertions(+)
 create mode 100644 spec/fixtures/models/pet.rb

diff --git a/spec/fixtures/models/pet.rb b/spec/fixtures/models/pet.rb
new file mode 100644
index 00000000..7f395f23
--- /dev/null
+++ b/spec/fixtures/models/pet.rb
@@ -0,0 +1,6 @@
+class Pet < CouchRest::Model::Base
+  property :name, String
+
+  belongs_to :walker, :class_name => 'Parent'
+  belongs_to :owner, :class_name => 'Parent'
+end

From 3dbabb29c24ca512b1d35cde4f06ea8382c735a7 Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Sun, 15 Mar 2015 23:28:26 +0000
Subject: [PATCH 18/21] add documentation for revers_associations

---
 lib/couchrest/model/associations.rb | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index 02a7885c..18d15643 100644
--- a/lib/couchrest/model/associations.rb
+++ b/lib/couchrest/model/associations.rb
@@ -18,8 +18,8 @@ module ClassMethods
         # An attribute will be created matching the name of the attribute
         # with '_id' on the end, or the foreign key (:foreign_key) provided.
         #
-        # Searching for the assocated object is performed using a string
-        # (:proxy) to be evaulated in the context of the owner. Typically
+        # Searching for the associated object is performed using a string
+        # (:proxy) to be evaluated in the context of the owner. Typically
         # this will be set to the class name (:class_name), or determined
         # automatically if the owner belongs to a proxy object.
         #
@@ -35,9 +35,16 @@ module ClassMethods
         #
         #    self.company.clients
         #
-        # If the name of the collection proxy is not the pluralized assocation name,
+        # If the name of the collection proxy is not the pluralized association name,
         # it can be set with the :proxy_name option.
         #
+        # If the owner model define an association back to the belonged model, setting
+        # the owner will also set the (:reverse_association) attribute of the owner.
+        # After such affectation, saving the object model will also trigger the save of
+        # the owner object.
+        # (:reverse_association) is optional and should be used only to remove ambiguity,
+        # when it can't be calculated from the (:class_name)
+        #
         def belongs_to(attrib, *options)
           opts = merge_belongs_to_association_options(attrib, options.first)
 
@@ -89,6 +96,14 @@ def belongs_to(attrib, *options)
         # NOTE: This method is *not* recommended for large collections or collections that change
         # frequently! Use with prudence.
         #
+        # If the associated model define an association back to the collection owner model, adding
+        # or removing from the collection will also populate the (:reverse_association) attribute
+        # of associated model.
+        # After such affectation, saving the object model will also trigger the save of
+        # the associated object.
+        # (:reverse_association) is optional and should be used only to remove ambiguity,
+        # when it can't be calculated from the (:class_name)
+        #
         def collection_of(attrib, *options)
           opts = merge_belongs_to_association_options(attrib, options.first)
           opts[:foreign_key] = opts[:foreign_key].pluralize

From 8274b9d2427954f1e58629a7f35c0960a61240c0 Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Fri, 10 Apr 2015 22:38:49 +0200
Subject: [PATCH 19/21] [back_assignments] activate back assignement only if
 the reverse_association is specified.

---
 lib/couchrest/model/associations.rb |  14 +---
 spec/fixtures/models/kid.rb         |   4 +-
 spec/unit/assocations_dual_spec.rb  | 102 ++++++++++++++++------------
 3 files changed, 62 insertions(+), 58 deletions(-)

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index 18d15643..ecacf590 100644
--- a/lib/couchrest/model/associations.rb
+++ b/lib/couchrest/model/associations.rb
@@ -212,21 +212,13 @@ def #{attrib}=(value)
 
       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
+          prop = self.class.properties.detect { |prop|  prop.name =~ %r{#{reverse_association.to_s.singularize}_ids?} }
+          raise "Cannot find reverse association: #{reverse_association}" unless prop
+          if attributes[prop.name].class.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
 
diff --git a/spec/fixtures/models/kid.rb b/spec/fixtures/models/kid.rb
index 518ef2d5..fd9b73c1 100644
--- a/spec/fixtures/models/kid.rb
+++ b/spec/fixtures/models/kid.rb
@@ -1,7 +1,7 @@
 class  Kid < CouchRest::Model::Base
   property :name, String
 
-  belongs_to :dad, :class_name => 'Parent'
-  belongs_to :mum, :class_name => 'Parent'
+  belongs_to :dad, :class_name => 'Parent', :reverse_association => :children
+  belongs_to :mum, :class_name => 'Parent', :reverse_association => :children
 
 end
diff --git a/spec/unit/assocations_dual_spec.rb b/spec/unit/assocations_dual_spec.rb
index 89657f79..9e9b16bf 100644
--- a/spec/unit/assocations_dual_spec.rb
+++ b/spec/unit/assocations_dual_spec.rb
@@ -11,10 +11,10 @@
 
   describe 'of type belongs_to' do
     context 'with the other side also belongs_to (1-1)' do
-      context '[non ambiguous association]' do
-        it 'should set the other side property too' do
+      context 'when reverse association not specified' do
+        it 'should NOT set the other side' do
           father.super_power = can_fly
-          can_fly.parent.should eql father
+          can_fly.parent.should be_nil
         end
       end
 
@@ -69,77 +69,89 @@
   describe 'of type collection_of' do
     context 'with the other side is a belongs_to (n-1).' do
       context 'Adding to the collection using <<' do
-        it 'should populate the belongs_to property' do
-          father.children << kid
-          kid.dad.should eq(father)
+        context 'when NO reverse_assocition is specified' do
+          it 'should populate the belongs_to property' do
+            father.children << kid
+            kid.dad.should be_nil
+          end
         end
         context 'when reverse_association is specified' do
           it 'should populate the belongs_to property' do
             father.pets << dog
             dog.owner.should eq(father)
           end
-        end
-        describe 'when object is saved' do
-          it 'should also save other side' do
-            father.children << kid
-            kid.should_receive(:save)
-            father.save
+          describe 'when object is saved' do
+            it 'should also save other side' do
+              father.children << kid
+              kid.should_receive(:save)
+              father.save
+            end
           end
         end
       end
 
       context 'Adding to the collection using push' do
-        it 'should populate the belongs_to property' do
-          father.children.push kid
-          kid.dad.should eq(father)
+        context 'when NO reverse_assocition is specified' do
+          it 'should populate the belongs_to property' do
+            father.children.push kid
+            kid.dad.should be_nil
+          end
         end
         context 'when reverse_association is specified' do
           it 'should populate the belongs_to property' do
             father.pets.push dog
             dog.owner.should eq(father)
           end
-        end
-        describe 'when object is saved' do
-          it 'should also save other side' do
-            father.children.push kid
-            kid.should_receive(:save)
-            father.save
+          describe 'when object is saved' do
+            it 'should also save other side' do
+              father.children.push kid
+              kid.should_receive(:save)
+              father.save
+            end
           end
         end
       end
 
       context 'Adding to the collection using unshift' do
-        it 'should populate the belongs_to property' do
-          father.children.unshift kid
-          kid.dad.should eq(father)
-        end
-        it 'should populate the belongs_to property' do
-          father.pets.unshift dog
-          dog.owner.should eq(father)
-        end
-        describe 'when object is saved' do
-          it 'should also save other side' do
+        context 'when NO reverse_assocition is specified' do
+          it 'should NOT populate the belongs_to property' do
             father.children.unshift kid
-            kid.should_receive(:save)
-            father.save
+            kid.dad.should be_nil
+          end
+        end
+        context 'when a reverse_assocition is specified' do
+          it 'should populate the belongs_to property' do
+            father.pets.unshift dog
+            dog.owner.should eq(father)
+          end
+          describe 'when object is saved' do
+            it 'should also save other side' do
+              father.pets.unshift dog
+              dog.should_receive(:save)
+              father.save
+            end
           end
         end
       end
 
       context 'Adding to the collection using [n]=' do
-        it 'should populate the belongs_to property' do
-          father.children[3]= kid
-          kid.dad.should eq(father)
-        end
-        it 'should populate the belongs_to property' do
-          father.pets[3] = dog
-          dog.owner.should eq(father)
+        context 'when NO reverse_assocition is specified' do
+          it 'should NOT populate the belongs_to property' do
+            father.children[3]= kid
+            kid.dad.should be_nil
+          end
         end
-        describe 'when object is saved' do
-          it 'should also save other side' do
-            father.children[4] = kid
-            kid.should_receive(:save)
-            father.save
+        context 'when a reverse_assocition is specified' do
+          it 'should populate the belongs_to property' do
+            father.pets[3] = dog
+            dog.owner.should eq(father)
+          end
+          describe 'when object is saved' do
+            it 'should also save other side' do
+              father.pets[4] = dog
+              dog.should_receive(:save)
+              father.save
+            end
           end
         end
       end

From bd6c4dae79e4447ca9334b84b98008b4b25d31ba Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Fri, 10 Apr 2015 22:54:12 +0200
Subject: [PATCH 20/21] [back_assignments] update README

---
 README.md | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 590cdb1b..94c9bc4d 100644
--- a/README.md
+++ b/README.md
@@ -107,7 +107,7 @@ $ rails generate couchrest_model:config
 $ rails generate model person --orm=couchrest_model
 ```
 
-## General Usage 
+## General Usage
 
 ```ruby
 require 'couchrest_model'
@@ -140,6 +140,20 @@ end
 @cat.update_attributes(:name => 'Felix', :random_text => 'feline')
 @cat.new? # false
 @cat.random_text  # Raises error!
+
+### reverse associations
+class Parent < CouchRest::Model::Base
+  collection_of :children
+end
+
+class Child < CouchRest::Model::Base
+  belongs_to :dad, class: Parent, :reverse_association => :children
+end
+
+@bob   = Parent.new
+@kevin = Child.new
+@kevin.dad = @bob
+@bob.children.include?(@kevin) # true
 ```
 
 ## Development

From de2bfc3c06149728bb5ae3a55044acf209729f6a Mon Sep 17 00:00:00 2001
From: yann ARMAND <yarmand@yammer-inc.com>
Date: Fri, 10 Apr 2015 23:04:17 +0200
Subject: [PATCH 21/21] [back_assignments] update documentation.

---
 lib/couchrest/model/associations.rb | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index ecacf590..9170e51c 100644
--- a/lib/couchrest/model/associations.rb
+++ b/lib/couchrest/model/associations.rb
@@ -42,8 +42,8 @@ module ClassMethods
         # the owner will also set the (:reverse_association) attribute of the owner.
         # After such affectation, saving the object model will also trigger the save of
         # the owner object.
-        # (:reverse_association) is optional and should be used only to remove ambiguity,
-        # when it can't be calculated from the (:class_name)
+        # (:reverse_association) is optional. When used, saving the belonged object will
+        # trigger the save of the owner object.
         #
         def belongs_to(attrib, *options)
           opts = merge_belongs_to_association_options(attrib, options.first)
@@ -101,8 +101,8 @@ def belongs_to(attrib, *options)
         # of associated model.
         # After such affectation, saving the object model will also trigger the save of
         # the associated object.
-        # (:reverse_association) is optional and should be used only to remove ambiguity,
-        # when it can't be calculated from the (:class_name)
+        # (:reverse_association) is optional. When used, saving the object with a collection will
+        # trigger save of the new members of the collection.
         #
         def collection_of(attrib, *options)
           opts = merge_belongs_to_association_options(attrib, options.first)