似乎在rails中你可以在两个地方定义关联验证,或者在关联本身上:
class Child
belongs_to :parent, :validate => true
end
或者作为验证回调:
class Child
belongs_to :parent
validates_associated :parent
end
这两种方法有什么区别？
测试差异
我想也许前者会创建一个背压,并强制父母只有在孩子有效的情况下才有效:
即(设置时:validate => true)
child.valid? # => false
child.parent.valid? # => also evaluates to false because of the :validate => true condition
# do whatever it takes to make the child valid again
#...
child.valid? # => true
child.parent.valid? # => true
但是我测试了它,但这不会发生.那两种方法之间有什么区别(如果有的话)？
给出以下代码：
from typing import Tuple
class Grandparent:
items: Tuple[str, ...] = ()
class Parent(Grandparent):
items = ('foo',)
class Child(Parent):
items = ('foo', 'bar')
mypy报告以下错误：
error: Incompatible types in assignment (expression has type "Tuple[str, str]", base class "Parent" defined the type as "Tuple[str]")
像这样更改代码（在Parent类中再次指定相同的类型）满足mypy：
error: Incompatible types in assignment (expression has type "Tuple[str, str]", base class "Parent" defined the type as "Tuple[str]")
鉴于所有位置items的分配都满足相同/原始定义，为什么我需要在类层次结构中的多个位置重新指定相同的类型？items有没有办法避免这样做？