1 files changed, 83 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/associations/builder/belongs_to.rb b/activerecord/lib/active_record/associations/builder/belongs_to.rb
new file mode 100644
index 0000000000..964e7fddc8
--- /dev/null
+++ b/activerecord/lib/active_record/associations/builder/belongs_to.rb
@@ -0,0 +1,83 @@
+module ActiveRecord::Associations::Builder
+  class BelongsTo < SingularAssociation #:nodoc:
+    self.macro = :belongs_to
+
+    self.valid_options += [:foreign_type, :polymorphic, :touch]
+
+    def constructable?
+      !options[:polymorphic]
+    end
+
+    def build
+      reflection = super
+      add_counter_cache_callbacks(reflection) if options[:counter_cache]
+      add_touch_callbacks(reflection)         if options[:touch]
+      configure_dependency
+      reflection
+    end
+
+    private
+
+      def add_counter_cache_callbacks(reflection)
+        cache_column = reflection.counter_cache_column
+        name         = self.name
+
+        method_name = "belongs_to_counter_cache_after_create_for_#{name}"
+        model.redefine_method(method_name) do
+          record = send(name)
+          record.class.increment_counter(cache_column, record.id) unless record.nil?
+        end
+        model.after_create(method_name)
+
+        method_name = "belongs_to_counter_cache_before_destroy_for_#{name}"
+        model.redefine_method(method_name) do
+          record = send(name)
+          record.class.decrement_counter(cache_column, record.id) unless record.nil?
+        end
+        model.before_destroy(method_name)
+
+        model.send(:module_eval,
+          "#{reflection.class_name}.send(:attr_readonly,\"#{cache_column}\".intern) if defined?(#{reflection.class_name}) && #{reflection.class_name}.respond_to?(:attr_readonly)", __FILE__, __LINE__
+        )
+      end
+
+      def add_touch_callbacks(reflection)
+        name        = self.name
+        method_name = "belongs_to_touch_after_save_or_destroy_for_#{name}"
+        touch       = options[:touch]
+
+        model.redefine_method(method_name) do
+          record = send(name)
+
+          unless record.nil?
+            if touch == true
+              record.touch
+            else
+              record.touch(touch)
+            end
+          end
+        end
+
+        model.after_save(method_name)
+        model.after_touch(method_name)
+        model.after_destroy(method_name)
+      end
+
+      def configure_dependency
+        if options[:dependent]
+          unless [:destroy, :delete].include?(options[:dependent])
+            raise ArgumentError, "The :dependent option expects either :destroy or :delete (#{options[:dependent].inspect})"
+          end
+
+          method_name = "belongs_to_dependent_#{options[:dependent]}_for_#{name}"
+          model.send(:class_eval, <<-eoruby, __FILE__, __LINE__ + 1)
+            def #{method_name}
+              association = #{name}
+              association.#{options[:dependent]} if association
+            end
+          eoruby
+          model.after_destroy method_name
+        end
+      end
+  end
+end