belongs_to (ActiveRecord::Associations::ClassMethods)

    # File lib/active_record/associations.rb, line 1029
          def belongs_to(association_id, options = {})
            reflection = create_belongs_to_reflection(association_id, options)

            if reflection.options[:polymorphic]
              association_accessor_methods(reflection, BelongsToPolymorphicAssociation)
            else
              association_accessor_methods(reflection, BelongsToAssociation)
              association_constructor_method(:build,  reflection, BelongsToAssociation)
              association_constructor_method(:create, reflection, BelongsToAssociation)
            end

            add_counter_cache_callbacks(reflection)          if options[:counter_cache]
            add_touch_callbacks(reflection, options[:touch]) if options[:touch]

            configure_dependency_for_belongs_to(reflection)
          end