Rails 自引用属性继承

Question

我有一个名为 Option 的模型，它具有自引用关联。一个选项可以有多个子选项，一个子选项可以有一个父选项。我还使用 cocoon gem 的嵌套属性在 form_for 选项上创建多个子选项。在表单上创建选项时，我可以动态创建子选项。

视图/选项/_form.html.erb：

<%= form_for @option do |f| %>

  <p>
    <%= f.label :name %><br>
    <%= f.text_field :name %><br>
    <%= f.label :activity %><br>
    <%= f.select :activity_id, options_for_select(activity_array, @option.activity_id)%><br>
  </p>

  <div>
    <div id="suboptions">
      <%= f.fields_for :suboptions do |suboption| %>
        <%= render 'suboption_fields', f: suboption %>
      <% end %>

      <div class="links">
        <%= link_to_add_association 'add suboption', f, :suboptions %>
      </div>
    </div>
  </div>

  <p>
    <%= f.submit "Send" %>
  </p>
<% end %>

模型/选项.rb：

class Option < ApplicationRecord
  belongs_to :activity
  has_many :option_students
  has_many :students, through: :option_students
  has_many :suboptions, class_name: "Option", foreign_key: "option_id"
  belongs_to :parent, class_name: "Option", optional: true, foreign_key: "option_id"
  accepts_nested_attributes_for :suboptions, allow_destroy: true,
    reject_if: ->(attrs) { attrs['name'].blank? }

  validates :name, presence: true

  after_initialize :set_defaults
  before_update :set_defaults


  def set_defaults
      self.suboptions.each do |sbp|
        sbp.activity_id = self.activity_id
      end
  end

end

参数：

def option_params
    params.require(:option).permit(:name, :activity_id, :students_ids => [], suboptions_attributes: [:id, :name, activity_id, :_destroy])
  end

我希望每个子选项在创建和更新时都从父项继承 activity_id 属性。我通过在模型上使用 set_defaults 方法尝试了这种方式，它适用于具有新嵌套子选项的新选项，如果我更新父项的活动 ID，它也会更新子选项的活动 ID。但是如果我在更新时创建另一个子选项，它不会将属性从父项传递给新的子选项。

Answer 1

您可以使用 before_validation 回调。例如，

测试代码

class Location < ApplicationRecord
  has_many :children, class_name: 'Location', foreign_key: 'parent_id'
  accepts_nested_attributes_for :children
  before_validation :initialize_children

  attr_accessor :activity

  def initialize_children
    children.each { |c| c.activity_id = self.activity_id }
  end
end

Rails 控制台

irb(main):002:0> Location.create({name: "L10", activity_id: 200, :children_attributes => [{name: "L12"}]})
   (0.1ms)  begin transaction
  SQL (1.1ms)  INSERT INTO "locations" ("name", "activity_id", "created_at", "updated_at") VALUES (?, ?, ?, ?)  [["name", "L10"], ["activity_id", 200], ["created_at", 2017-01-11 04:07:26 UTC], ["updated_at", 2017-01-11 04:07:26 UTC]]
  SQL (0.1ms)  INSERT INTO "locations" ("name", "parent_id", "activity_id", "created_at", "updated_at") VALUES (?, ?, ?, ?, ?)  [["name", "L12"], ["parent_id", "1"], ["activity_id", 200], ["created_at", 2017-01-11 04:07:26 UTC], ["updated_at", 2017-01-11 04:07:26 UTC]]
   (3.7ms)  commit transaction
=> #<Location id: 1, name: "L10", parent_id: nil, activity_id: 200, created_at: "2017-01-11 04:07:26", updated_at: "2017-01-11 04:07:26">
irb(main):003:0> Location.all
  Location Load (0.2ms)  SELECT "locations".* FROM "locations"
=> #<ActiveRecord::Relation [#<Location id: 1, name: "L10", parent_id: nil, activity_id: 200, created_at: "2017-01-11 04:07:26", updated_at: "2017-01-11 04:07:26">, #<Location id: 2, name: "L12", parent_id: "1", activity_id: 200, created_at: "2017-01-11 04:07:26", updated_at: "2017-01-11 04:07:26">]>
irb(main):004:0> Location.last
  Location Load (0.2ms)  SELECT  "locations".* FROM "locations" ORDER BY "locations"."id" DESC LIMIT ?  [["LIMIT", 1]]
=> #<Location id: 2, name: "L12", parent_id: "1", activity_id: 200, created_at: "2017-01-11 04:07:26", updated_at: "2017-01-11 04:07:26">

Answer 2

升级到 Rails 5 时我也遇到了同样的问题。Fossil 的回答有所帮助，但我还必须做一件事：

1. 在主对象的has_many关系中添加inverse_of（在本例中为Activity模型：has_many :options, inverse_of: "activity"
2. 在自引用对象的has_many关系中添加inverse_of（在本例中为Option模型：has_many :suboptions, inverse_of: "parent"
3. 在自引用模型（此处为Option）中，使用before_validation 回调传递主对象：

class Option
  belongs_to :parent, foreign_key: "option_id", class_name: "Option"
  has_many :suboptions, class_name: "Option", foreign_key: "option_id", inverse_of: "parent"

  before_validation :pass_activity_to_suboptions

  private
  define pass_activity_to_suboptions
    suboptions.each { |o| o.activity = self.activity }
  end
end