belongs_to (ActiveRecord::Associations::ClassMethods)

    # File lib/active_record/associations.rb, line 987
          def belongs_to(association_id, options = {})
            reflection = create_belongs_to_reflection(association_id, options)

            ivar = "@#{reflection.name}"

            if reflection.options[:polymorphic]
              association_accessor_methods(reflection, BelongsToPolymorphicAssociation)

              method_name = "polymorphic_belongs_to_before_save_for_#{reflection.name}".to_sym
              define_method(method_name) do
                association = instance_variable_get(ivar) if instance_variable_defined?(ivar)

                if association && association.target
                  if association.new_record?
                    association.save(true)
                  end

                  if association.updated?
                    self[reflection.primary_key_name] = association.id
                    self[reflection.options[:foreign_type]] = association.class.base_class.name.to_s
                  end
                end
              end
              before_save method_name
            else
              association_accessor_methods(reflection, BelongsToAssociation)
              association_constructor_method(:build,  reflection, BelongsToAssociation)
              association_constructor_method(:create, reflection, BelongsToAssociation)

              method_name = "belongs_to_before_save_for_#{reflection.name}".to_sym
              define_method(method_name) do
                association = instance_variable_get(ivar) if instance_variable_defined?(ivar)

                if !association.nil?
                  if association.new_record?
                    association.save(true)
                  end

                  if association.updated?
                    self[reflection.primary_key_name] = association.id
                  end
                end
              end
              before_save method_name
            end

            # Create the callbacks to update counter cache
            if options[:counter_cache]
              cache_column = options[:counter_cache] == true ?
                "#{self.to_s.demodulize.underscore.pluralize}_count" :
                options[:counter_cache]

              method_name = "belongs_to_counter_cache_after_create_for_#{reflection.name}".to_sym
              define_method(method_name) do
                association = send(reflection.name)
                association.class.increment_counter(cache_column, send(reflection.primary_key_name)) unless association.nil?
              end
              after_create method_name

              method_name = "belongs_to_counter_cache_before_destroy_for_#{reflection.name}".to_sym
              define_method(method_name) do
                association = send(reflection.name)
                association.class.decrement_counter(cache_column, send(reflection.primary_key_name)) unless association.nil?
              end
              before_destroy method_name

              module_eval(
                "#{reflection.class_name}.send(:attr_readonly,\"#{cache_column}\".intern) if defined?(#{reflection.class_name}) && #{reflection.class_name}.respond_to?(:attr_readonly)"
              )
            end

            add_single_associated_validation_callbacks(reflection.name) if options[:validate] == true

            configure_dependency_for_belongs_to(reflection)
          end