【问题标题】：Referencing the same model 3 times from another model in Mongoid从 Mongoid 中的另一个模型引用相同模型 3 次
【发布时间】：2014-08-01 19:57:37
【问题描述】：

我有两个模型如下：

class Tag
  include Mongoid::Document
  include Mongoid::Timestamps
  belongs_to :group
end

class Group
  include Mongoid::Document
  include Mongoid::Timestamps

  has_one :user_tag, :class_name => 'Tag', :foreign_key => "user_tag_id", :inverse_of => nil
  has_one :tag_tag, :class_name => 'Tag', :foreign_key => "tag_tag_id", :inverse_of => nil
  has_one :group_tag, :class_name => 'Tag', :foreign_key => "group_tag_id", :inverse_of => nil
end

但是这种尝试和其他尝试似乎并没有产生预期的结果，即让 3 种不同类型的 Group 分别可引用。任何帮助将不胜感激！

【问题讨论】：

标签： ruby activerecord mongoid mongoid3

【解决方案1】：

我认为以下内容可以满足您的需求，尽管还有三个额外的琐碎模型/子类。我尝试仅使用 Tag 类并且没有子类遇到冲突和其他问题与反比关系，即使在放松多态性限制时也是如此。也许这三个额外的琐碎子类可以满足您的目的？请注意，标签数据仍存储在“store_in”方法指定的一个“标签”集合中。

app/models/group.rb

class Group
  include Mongoid::Document
  include Mongoid::Timestamps
  field :name, type: String

  has_one :user_tag
  has_one :tag_tag
  has_one :group_tag
end

app/models/tag.rb

class Tag
  include Mongoid::Document
  include Mongoid::Timestamps
  field :text, type: String

  belongs_to :group
  store_in collection: 'tag'
end

app/models/group_tag.rb

class GroupTag < Tag
end

app/models/tag_tag.r

class TagTag < Tag
end

app/models/user_tag.rb

class UserTag < Tag
end

test/unit/group_test.rb

require 'test_helper'
require 'pp'

class GroupTest < ActiveSupport::TestCase
  def setup
    Mongoid.default_session.drop
  end
  test '0. mongoid version' do
    puts "\nMongoid::VERSION:#{Mongoid::VERSION}\nMoped::VERSION:#{Moped::VERSION}"
  end
  test 'multiple tag references' do
    group = Group.create(name: 'my group')
    group.user_tag = UserTag.create(text: 'user tag')
    group.tag_tag = TagTag.create(text: 'tag tag')
    group.group_tag = GroupTag.create(text: 'group tag')
    assert_equal(1, Group.count)
    assert_equal(3, Tag.count)
    puts
    puts "Group:"
    pp Group.all.to_a
    puts "Tag:"
    pp Tag.all.to_a
    puts "collections: #{Mongoid.default_session.collection_names.inspect}"
  end
end

耙式测试

运行选项：

运行测试：

[1/2] GroupTest#test_0._mongoid_version
Mongoid::VERSION:3.1.6
Moped::VERSION:1.5.2
[2/2] GroupTest#test_multiple_tag_references
Group:
[#<Group _id: 53f242b27f11ba5f31000001, created_at: 2014-08-18 18:15:14 UTC, updated_at: 2014-08-18 18:15:14 UTC, name: "my group">]
Tag:
[#<UserTag _id: 53f242b27f11ba5f31000002, created_at: 2014-08-18 18:15:14 UTC, updated_at: 2014-08-18 18:15:14 UTC, text: "user tag", group_id: "53f242b27f11ba5f31000001", _type: "UserTag">,
 #<TagTag _id: 53f242b27f11ba5f31000003, created_at: 2014-08-18 18:15:14 UTC, updated_at: 2014-08-18 18:15:14 UTC, text: "tag tag", group_id: "53f242b27f11ba5f31000001", _type: "TagTag">,
 #<GroupTag _id: 53f242b27f11ba5f31000004, created_at: 2014-08-18 18:15:14 UTC, updated_at: 2014-08-18 18:15:14 UTC, text: "group tag", group_id: "53f242b27f11ba5f31000001", _type: "GroupTag">]
collections: ["groups", "tag"]
Finished tests in 0.527855s, 3.7889 tests/s, 3.7889 assertions/s.
2 tests, 2 assertions, 0 failures, 0 errors, 0 skips

【讨论】：