scope_association_reflection

# File activerecord/lib/active_record/relation/query_methods.rb, line 122
        def scope_association_reflection(association)
          reflection = @scope.klass._reflect_on_association(association)
          unless reflection
            raise ArgumentError.new("An association named `:#{association}` does not exist on the model `#{@scope.name}`.")
          end
          reflection
        end