ruby-on-rails - Rails 是否允许对 validates_related 进行条件验证？

Question

Rails 是否允许对 validates_related 进行条件验证？我在 Rails 4.2.0 上看到以下内容。我是否试图错误地做到这一点？

型号:

class User < ActiveRecord::Base
  has_many :books

  validates_associated :books, if: :should_validate_book?

  def should_validate_book?
    return false
  end
end

class Book < ActiveRecord::Base
  belongs_to :user

  validates_presence_of :title
end

Book 的 title 属性的存在验证仍然运行(Rails 控制台):

> u = User.create!
 => #<User id: 2, created_at: "2015-02-24 19:34:51", updated_at: "2015-02-24 19:34:51">
> u.books.build
 => #<Book id: nil, user_id: 3, title: nil, created_at: nil, updated_at: nil>
> u.valid?
 => false
> u.books.first.errors
 => #<ActiveModel::Errors:0x007fa256b210d8 @base=#<Book id: nil, user_id: 3, title: nil, created_at: nil, updated_at: nil>, @messages={:title=>["can't be blank"]}>

Answer 1

事实证明，对于 has_many，默认情况下 validates_related 是 ON 的。关系。要有条件地实现，您需要在 has_many 声明中添加 validate: false :

  has_many :books, validate: false