RAILS：如何在回调中创建新的collection.build？ [英] RAILS: How to make new collection.build in a callback?

问题描述

如何使用其他模型在after_save中创建一个新记录？

我试过这行结果是undefined method`journals'for nil：NilClass >

例如

 资源：users do 
 resource：profile 
 resources：journals 
 end 
 
 
 class User< ActiveRecord :: Base 
 has_one：profile 
 has_many：journals 
 end 
 
 class Profile< ActiveRecord :: Base 
 belongs_to：user 
 
 after_save：create_new_journal_if_none 
 
 private 
 def create_new_journal_if_none 
如果user.journals.empty？ ？ 
 user.journals.build（）???? 
 end 
 end 
 end 
 
 class Journals< ActiveRecord :: Base 
 belongs_to：user 
 end 
  

解决方案<

 
 
  class Profile< ActiveRecord :: Base 
 belongs_to：user 
 
 before_create do 
 user.journals.build unless user.journals.any？ 
 end 
 end 
  

这行代码将创建一个配置文件和一个日志分配给用户

  User.find（1）.create_profile（name：test）
  

How to create a new record in after_save using other model?

I tried this line which resulted "undefined method `journals' for nil:NilClass"

e.g.

resources :users do
  resource :profile
  resources :journals
end


class User < ActiveRecord::Base
  has_one  :profile
  has_many :journals
end

class Profile < ActiveRecord::Base
  belongs_to :user

  after_save :create_new_journal_if_none

  private
    def create_new_journal_if_none
      if user.journals.empty? ????
        user.journals.build() ????
      end
    end
end

class Journals < ActiveRecord::Base
  belong_to :user
end

解决方案

Nested models are going to be saved as well once parent saves, so it's easy to use before_create block and build a nested resource here.

class Profile < ActiveRecord::Base
  belongs_to :user

  before_create do 
    user.journals.build unless user.journals.any?
  end
end

This line of code will create a profile and a journal assigned with the User

User.find(1).create_profile(name :test)

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