Assign the association attributes to the associated record before the before_initialize callback of the record runs. Fixes #1842.

activerecord/CHANGELOG

@@ -1,5 +1,17 @@
 *Rails 3.1.0 (unreleased)*
 
+* ActiveRecord::MacroReflection::AssociationReflection#build_record has a new method signature.
+
+  Before: def build_association(*options)
+  After:  def build_association(*options, &block)
+
+  Users who are redefining this method to extend functionality should ensure that the block is
+  passed through to ActiveRecord::Base#new.
+
+  This change is necessary to fix https://github.com/rails/rails/issues/1842.
+
+  [Jon Leighton]
+
 * AR#pluralize_table_names can be used to singularize/pluralize table name of an individual model:
 
     class User < ActiveRecord::Base

activerecord/lib/active_record/associations/association.rb

@@ -224,6 +224,15 @@ def stale_state
         def association_class
           @reflection.klass
         end
+
+        def build_record(attributes, options)
+          reflection.build_association(attributes, options) do |record|
+            record.assign_attributes(
+              create_scope.except(*record.changed),
+              :without_protection => true
+            )
+          end
+        end
     end
   end
 end

activerecord/lib/active_record/associations/collection_association.rb

@@ -423,12 +423,6 @@ def create_scope
           scoped.scope_for_create.stringify_keys
         end
 
-        def build_record(attributes, options)
-          record = reflection.build_association(attributes, options)
-          record.assign_attributes(create_scope.except(*record.changed), :without_protection => true)
-          record
-        end
-
         def delete_or_destroy(records, method)
           records = records.flatten
           records.each { |record| raise_on_type_mismatch(record) }

activerecord/lib/active_record/associations/singular_association.rb

@@ -26,8 +26,7 @@ def create!(attributes = {}, options = {}, &block)
       end
 
       def build(attributes = {}, options = {})
-        record = reflection.build_association(attributes, options)
-        record.assign_attributes(create_scope.except(*record.changed), :without_protection => true)
+        record = build_record(attributes, options)
         yield(record) if block_given?
         set_new_record(record)
         record

activerecord/lib/active_record/reflection.rb

@@ -175,8 +175,8 @@ def initialize(macro, name, options, active_record)
 
       # Returns a new, unsaved instance of the associated class. +options+ will
       # be passed to the class's constructor.
-      def build_association(*options)
-        klass.new(*options)
+      def build_association(*options, &block)
+        klass.new(*options, &block)
       end
 
       # Creates a new instance of the associated class, and immediately saves it

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -1557,4 +1557,11 @@ def test_dont_call_save_callbacks_twice_on_has_many
     assert_equal 1, contract.hi_count
     assert_equal 1, contract.bye_count
   end
+
+  def test_association_attributes_are_available_to_after_initialize
+    car = Car.create(:name => 'honda')
+    bulb = car.bulbs.build
+
+    assert_equal car.id, bulb.attributes_after_initialize['car_id']
+  end
 end

activerecord/test/cases/associations/has_one_associations_test.rb

@@ -438,4 +438,11 @@ def test_create_bang_with_block
     bulb = car.create_bulb!{ |b| b.color = 'Red' }
     assert_equal 'RED!', bulb.color
   end
+
+  def test_association_attributes_are_available_to_after_initialize
+    car = Car.create(:name => 'honda')
+    bulb = car.create_bulb
+
+    assert_equal car.id, bulb.attributes_after_initialize['car_id']
+  end
 end

activerecord/test/models/bulb.rb

@@ -4,13 +4,18 @@ class Bulb < ActiveRecord::Base
 
   attr_protected :car_id, :frickinawesome
 
-  attr_reader :scope_after_initialize
+  attr_reader :scope_after_initialize, :attributes_after_initialize
 
   after_initialize :record_scope_after_initialize
   def record_scope_after_initialize
     @scope_after_initialize = self.class.scoped
   end
 
+  after_initialize :record_attributes_after_initialize
+  def record_attributes_after_initialize
+    @attributes_after_initialize = attributes.dup
+  end
+
   def color=(color)
     self[:color] = color.upcase + "!"
   end
@@ -28,4 +33,4 @@ def self.new(attributes = {}, options = {}, &block)
 end
 
 class CustomBulb < Bulb
-end
+end