Improved strategy for updating a belongs_to association when the foreign key...

Improved strategy for updating a belongs_to association when the foreign key changes. Rather than resetting each affected association when the foreign key changes, we should lazily check for 'staleness' (where fk does not match target id) when the association is accessed.

activerecord/lib/active_record/associations.rb

@@ -1229,14 +1229,12 @@ def belongs_to(association_id, options = {})
 
         if reflection.options[:polymorphic]
           association_accessor_methods(reflection, BelongsToPolymorphicAssociation)
-          association_foreign_type_setter_method(reflection)
         else
           association_accessor_methods(reflection, BelongsToAssociation)
           association_constructor_method(:build,  reflection, BelongsToAssociation)
           association_constructor_method(:create, reflection, BelongsToAssociation)
         end
 
-        association_foreign_key_setter_method(reflection)
         add_counter_cache_callbacks(reflection)          if options[:counter_cache]
         add_touch_callbacks(reflection, options[:touch]) if options[:touch]
 
@@ -1456,7 +1454,7 @@ def association_accessor_methods(reflection, association_proxy_class)
             force_reload = params.first unless params.empty?
             association = association_instance_get(reflection.name)
 
-            if association.nil? || force_reload
+            if association.nil? || force_reload || association.stale_target?
               association = association_proxy_class.new(self, reflection)
               retval = force_reload ? reflection.klass.uncached { association.reload } : association.reload
               if retval.nil? and association_proxy_class == BelongsToAssociation
@@ -1556,45 +1554,6 @@ def association_constructor_method(constructor, reflection, association_proxy_cl
           end
         end
 
-        def association_foreign_key_setter_method(reflection)
-          setters = reflect_on_all_associations(:belongs_to).map do |belongs_to_reflection|
-            if belongs_to_reflection.primary_key_name == reflection.primary_key_name
-              "association_instance_set(:#{belongs_to_reflection.name}, nil);"
-            end
-          end.compact.join
-
-          if method_defined?(:"#{reflection.primary_key_name}=")
-            undef_method :"#{reflection.primary_key_name}="
-          end
-
-          class_eval <<-FILE, __FILE__, __LINE__ + 1
-            def #{reflection.primary_key_name}=(new_id)
-              write_attribute :#{reflection.primary_key_name}, new_id
-              if #{reflection.primary_key_name}_changed?
-                #{ setters }
-              end
-            end
-          FILE
-        end
-
-        def association_foreign_type_setter_method(reflection)
-          setters = reflect_on_all_associations(:belongs_to).map do |belongs_to_reflection|
-            if belongs_to_reflection.options[:foreign_type] == reflection.options[:foreign_type]
-              "association_instance_set(:#{belongs_to_reflection.name}, nil);"
-            end
-          end.compact.join
-
-          field = reflection.options[:foreign_type]
-          class_eval <<-FILE, __FILE__, __LINE__ + 1
-            def #{field}=(new_id)
-              write_attribute :#{field}, new_id
-              if #{field}_changed?
-                #{ setters }
-              end
-            end
-          FILE
-        end
-
         def add_counter_cache_callbacks(reflection)
           cache_column = reflection.counter_cache_column
 

activerecord/lib/active_record/associations/association_proxy.rb

@@ -130,6 +130,16 @@ def loaded
         @loaded = true
       end
 
+      # The target is stale if the target no longer points to the record(s) that the
+      # relevant foreign_key(s) refers to. If stale, the association accessor method
+      # on the owner will reload the target. It's up to subclasses to implement this
+      # method if relevant.
+      #
+      # Note that if the target has not been loaded, it is not considered stale.
+      def stale_target?
+        false
+      end
+
       # Returns the target of this proxy, same as +proxy_target+.
       def target
         @target

activerecord/lib/active_record/associations/belongs_to_association.rb

@@ -42,6 +42,14 @@ def updated?
         @updated
       end
 
+      def stale_target?
+        if @target && @target.persisted?
+          @target.send(@reflection.association_primary_key).to_i != @owner.send(@reflection.primary_key_name).to_i
+        else
+          false
+        end
+      end
+
       private
         def find_target
           find_method = if @reflection.options[:primary_key]

activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb

@@ -23,6 +23,15 @@ def updated?
         @updated
       end
 
+      def stale_target?
+        if @target && @target.persisted?
+          @target.send(@reflection.association_primary_key).to_i != @owner.send(@reflection.primary_key_name).to_i ||
+          @target.class.base_class.name.to_s != @owner.send(@reflection.options[:foreign_type]).to_s
+        else
+          false
+        end
+      end
+
       private
 
         # NOTE - for now, we're only supporting inverse setting from belongs_to back onto

activerecord/lib/active_record/reflection.rb

@@ -209,7 +209,10 @@ def association_foreign_key
       end
 
       def association_primary_key
-        @association_primary_key ||= options[:primary_key] || klass.primary_key
+        @association_primary_key ||=
+          options[:primary_key] ||
+          !options[:polymorphic] && klass.primary_key ||
+          'id'
       end
 
       def active_record_primary_key

activerecord/test/cases/nested_attributes_test.rb

@@ -298,7 +298,7 @@ def test_should_accept_update_only_option
 
   def test_should_create_new_model_when_nothing_is_there_and_update_only_is_true
     @ship.delete
-    
+
     @pirate.reload.update_attributes(:update_only_ship_attributes => { :name => 'Mayflower' })
 
     assert_not_nil @pirate.ship
@@ -411,6 +411,7 @@ def test_should_take_a_hash_with_string_keys_and_update_the_associated_model
 
   def test_should_modify_an_existing_record_if_there_is_a_matching_composite_id
     @pirate.stubs(:id).returns('ABC1X')
+    @ship.stubs(:pirate_id).returns(@pirate.id) # prevents pirate from being reloaded due to non-matching foreign key
     @ship.pirate_attributes = { :id => @pirate.id, :catchphrase => 'Arr' }
 
     assert_equal 'Arr', @ship.pirate.catchphrase
@@ -451,7 +452,7 @@ def test_should_work_with_update_attributes_as_well
 
   def test_should_not_destroy_the_associated_model_until_the_parent_is_saved
     pirate = @ship.pirate
-    
+
     @ship.attributes = { :pirate_attributes => { :id => pirate.id, '_destroy' => true } }
     assert_nothing_raised(ActiveRecord::RecordNotFound) { Pirate.find(pirate.id) }
     @ship.save

activerecord/test/cases/reflection_test.rb

@@ -7,6 +7,7 @@
 require 'models/ship'
 require 'models/pirate'
 require 'models/price_estimate'
+require 'models/tagging'
 
 class ReflectionTest < ActiveRecord::TestCase
   include ActiveRecord::Reflection
@@ -194,6 +195,7 @@ def test_has_many_through_reflection
   def test_association_primary_key
     assert_equal "id", Author.reflect_on_association(:posts).association_primary_key.to_s
     assert_equal "name", Author.reflect_on_association(:essay).association_primary_key.to_s
+    assert_equal "id", Tagging.reflect_on_association(:taggable).association_primary_key.to_s
   end
 
   def test_active_record_primary_key