如果有孩子，我试图阻止记录被销毁。
class Submission < ActiveRecord::Base
has_many :quotations, :dependent => :destroy
before_destroy :check_for_payments
def quoted?
quotations.any?
end
def has_payments?
true if quotations.detect {|q| q.payment}
end
private
def check_for_payments
if quoted? && has_payments?
errors[:base] << "cannot delete submission that has already been paid"
false
end
end
end
class Quotation < ActiveRecord::Base
#associations
belongs_to :submission
has_one :payment_notification
has_one :payment
before_destroy :check_for_payments
private
def check_for_payments
if payment_notification || payment
errors[:base] << "cannot delete quotation while payment exist"
return false
end
end
end
当我测试此代码时，before_destroy：check_for_payments会阻止删除Quotation记录。
但是：提交before_destroy回调中的：check_for_payments不会停止提交被删除。
如何通过销毁付款来停止提交？
我会尝试下面的代码：
any?避免不必要的记录检索报价和付款，这导致使用关联计数器缓存（如果已定义），或者如果已经加载则关联的大小，并且如果需要则失败SQL COUNT。q.payment关联代理的真实性/存在性，这对has_xxx不起作用。如果你想测试存在使用q.payment.present?尝试以下操作，看看你如何去：
class Submission < ActiveRecord::Base
has_many :quotations,
inverse_of: :submission,
dependent: :destroy
has_many :payments,
through: :quotations
before_destroy :check_for_payments, prepend: true
private
def check_for_payments
if payments.any?
errors[:base] << "cannot delete submission that has already been paid"
return false
end
end
end
在Rails 5中你必须使用throw :abort否则它将无法工作。 （甚至返回false）
这样的事情应该有效：
class Something < ApplicationRecord
before_destroy :can_destroy?
private
def can_destroy?
if model.something?
errors[:base] << "Can't be destroy because of something"
throw :abort
end
end
http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html订购回调（我改变了这个具体例子的措辞）
有时代码需要回调以特定顺序执行。例如，在引用被+ dependent：destroy +选项销毁之前，应该执行before_destroy回调（在这种情况下为check_for_payments）。
在这种情况下，问题是当执行before_destroy回调时，引用不可用，因为首先执行destroy回调。您可以在before_destroy回调上使用prepend选项来避免这种情况。
before_destroy :check_for_payments, prepend: true
我用上面描述的相同模型制作了一个新应用程序，然后进行了提交测试。它非常难看，我只是在学习......
class Submission < ActiveRecord::Base
has_many :quotations, :dependent => :destroy
before_destroy :check_for_payments, prepend: true
def quoted?
quotations.any?
end
def has_payments?
true if quotations.detect {|q| q.payment }
end
private
def check_for_payments
if quoted? && has_payments?
errors[:base] << "error message"
false
end
end
end
class Quotation < ActiveRecord::Base
belongs_to :submission
has_one :payment_notification
has_one :payment
before_destroy :check_for_payments
private
def check_for_payments
if payment_notification || payment
errors[:base] << "cannot delete quotation while payment exist"
return false
end
end
end
require 'test_helper'
class SubmissionTest < ActiveSupport::TestCase
test "can't destroy" do
sub = Submission.new
sub.save
quote = Quotation.new
quote.submission_id = sub.id
quote.save
pay = Payment.new
pay.quotation_id = quote.id
pay.save
refute sub.destroy, "destroyed record"
end
end
它过去了！我希望有所帮助。
据我所知，当对与Submission有关联的类（dependent => :destroy）的对象调用destroy时，如果相关模型中的任何回调失败，在你的情况下Quotation，那么Submission类对象仍将被删除。
所以为了防止这种行为，我们必须考虑到目前可以想到的方法：
1）不是在Quotation#check_for_payments中返回false，而是可以引发异常并在Submission模型中优雅地处理它，这将完成ROLLBACK，并且不会让任何记录被破坏。
2）您可以检查quotations实例中的任何Submission是否在payment方法本身中具有payment_notification / Submission#check_for_payments，这将阻止删除Submission对象。
确保quoted?和has_payments?不会返回false。
有关调试，请试试这个
def check_for_payments
raise "Debugging #{quoted?} #{has_payments?}" # Make sure both are true
if quoted? && has_payments?
errors[:base] << "cannot delete submission that has already been paid"
false
end
end
在Rails 5中你还可以：
def destroy
quoted? && has_payments? ? self : super
end
submission.destroy # => submission
submission.destroyed? # => true/false