Question

我遇到了一个奇怪的问题，阅读回调RoR指南没有给我答案。

class User < ActiveRecord::Base
...
has_many :company_users, dependent: :destroy
has_many :companies, through: :company_users
has_many :user_teams, dependent: :destroy
has_many :teams, through: :user_teams

before_create :check_company!
after_create :check_team

def check_company!
  return if self.companies.present?
  domain = self.email_domain
  company = Company.find_using_domain(domain)
  if company.present?
    assign_company(company)
  else
    create_and_assign_company(domain)
  end
end 

def check_team
  self.companies.each do |company|
    #do stuff
  end
end
...
end

after_create：check_team回调面临问题，因为行

self.companies.each do |company|

这里，即使创建了公司和用户并且用户与之关联，self.companies也会返回一个空数组[]。我知道我可以通过使它成为before_create回调来解决它。但我很困惑！

为什么after_create回调在提交后无法访问自己的关联？

解决方案：请在接受的答案中阅读我的评论，以了解问题的原因和解决方案。

Answer 1

在before_create内部回调中，记录的id尚未可用，因为它在...之前创建...所以它还没有在数据库中持久存在id。这意味着关联的company_user记录尚未具有user_id值，正是因为此时user.id仍为nil。但是，Rails让你不必担心这个＆＃34;鸡蛋和鸡蛋＆＃34;问题，只要你做得正确：

我重新创建了您的设置（Company，User和CompanyUser模型），以下内容适合您的情况（经过测试的工作）：

class User < ApplicationRecord
  has_many :company_users, dependent: :destroy
  has_many :companies, through: :company_users

  before_create :check_company!
  after_create :check_team

  def check_company!
    # use `exists?` instead of `present?` because `exists?` is a lot faster and efficient as it generates with a `LIMIT 1` SQL.
    return if companies.exists?

    ## when assigning an already persisted Company record:
    example_company = Company.first
    # 1) WORKS
    companies << example_company
    # 2) WORKS
    company_users.build(company: example_company)

    ## when assigning and creating a new Company record:
    # 1) WORKS (this company record will be automatically saved/created after this user record is saved in the DB)
    companies.build(name: 'ahaasdfwer') # or... self.companies.new(name: 'ahaasdfwer')
    # 2) DOES NOT WORK, because you'll receive an error `ActiveRecord::RecordNotSaved: You cannot call create unless the parent is saved`
    companies.create(name: 'ahaasdfwer')
  end

  def check_team
    puts companies.count
    # => 1 if "worked"
    puts companies.first.persisted?
    # => true if "worked"
  end
end

after_create无权访问在before_created回调期间创建的关联记录？

1 个答案: