验证失败,字段必须与allow_nil一起存在

我正在创建一个博客,文章可以回复其他文章.文章也可以是群体的一部分.但是,文章不必属于一个组或是对另一篇文章的回应.

我正在尝试按照Rails文档创建文章作为自联接记录.

我创建了用户,组和文章脚手架:

bin/rails g scaffold user username:string email:string birthday:date

bin/rails g scaffold group name:string user:references

bin/rails g scaffold article user:references parent:references title:string subheading:string body:text pub_date:datetime group:references hidden:boolean prompt:boolean

我正试图allow_nil在模型验证中使用.

class Article < ApplicationRecord
  belongs_to :user
  belongs_to :parent, class_name: "Article"
  has_many :replies, class_name: "Article", foreign_key: "parent_id"
  belongs_to :group

  validates :parent, length: {minimum: 1}, allow_nil: true
  validates :group, length: {minimum: 1}, allow_nil: true
end

但是当我运行db:seed时:

user1 = User.create(username: "pete01",email: "pete01@gmail.com",
    birthday:"1980-01-30")

article1 = Article.create!(user:user1, parent:nil, title:"My First Article",
        subheading:"This is important", body:"The body of my first article",
        pub_date:"2015-12-26", group:nil, hidden:false, prompt:false)

我收到此错误:

ActiveRecord::RecordInvalid: Validation failed: Parent must exist, Group must exist

是否有其他地方我应该告诉Rails它不需要验证Group和Parent？

解决方法是找到该文件new_framework_defaults.rb,将其更改为false:

Rails.application.config.active_record.belongs_to_required_by_default = false