Question

class Address
    has_one :order
end

class Order
    index({address_id: 1, background: true})
    belongs_to :address
end

订单将始终具有address_id，但地址可以存在而不与订单相关。我试图找到没有订单的所有地址，以便order.address_id == address.id。我怎么能这样做？

Answer 1

在下面的测试中，方法addresses_without_an_order通过Rails / Mongoid回答您的问题。它既简单又直接，但效率低下，这对您来说可能不重要。为了进一步启发，我们假设你想要更高效的东西。通过Order集合上的外键引用address_id实现1对1关系。因此，对Address集合的简单查询无法回答您的问题。 MongoDB不会在两个集合之间实现连接（放弃连接以支持分片）。

要在MongoDB中以更高的效率获得等效的连接，请将子项嵌入父项中。 address_without_a_contact方法显示了使用嵌入来回答问题的难易程度。对于1对1的关系，嵌入很容易且明显，并且具有比加入更高的性能。希望这能回答你的问题。

应用程序/模型/ address.rb

class Address
  include Mongoid::Document
  has_one :order
  embeds_one :contact
end

应用程序/模型/ order.rb

class Order
  include Mongoid::Document
  index({address_id: 1}, {background: true})
  belongs_to :address
end

应用程序/模型/ contact.rb

class Contact
  include Mongoid::Document
  embedded_in :address
end

测试/单元/ address_test.rb

require 'test_helper'

class AddressTest < ActiveSupport::TestCase
  def setup
    Address.delete_all
    Order.delete_all
    puts
  end
  test "0. mongoid version" do
    puts "Mongoid::VERSION:#{Mongoid::VERSION}\nMoped::VERSION:#{Moped::VERSION}"
  end
  def addresses_without_an_order
    Address.all.collect{|address| address.order == nil ? address : nil}.compact
  end
  def addresses_without_a_contact
    Address.where(:contact.exists => false).to_a
  end
  test "Address" do
    address = Address.create(street: "229 W 43rd Street, 5th FL", city: "New York", state: "NY", zip: "10036")
    assert_equal 1, Address.count
    puts "addresses_without_an_order: #{addresses_without_an_order.inspect}"
    puts "addresses_without_a_contact: #{addresses_without_a_contact.inspect}"
    address.order = Order.create(ASIN: "B00DUW4BMS", title: "The C++ Programming Language (4th Edition)", author: "Bjarne Stroustrup")
    address.contact = Contact.new(name: "Isabel")
    assert_equal 1, Order.count
    assert_equal [], addresses_without_an_order
    assert_equal [], addresses_without_a_contact
  end
end

$ rake test

Run options:

# Running tests:

[1/2] AddressTest#test_0._mongoid_version
Mongoid::VERSION:3.1.5
Moped::VERSION:1.5.1
[2/2] AddressTest#test_Address
addresses_without_an_order: [#<Address _id: 528a5fa37f11ba7227000001, street: "229 W 43rd Street, 5th FL", city: "New York", state: "NY", zip: "10036">]
addresses_without_a_contact: [#<Address _id: 528a5fa37f11ba7227000001, street: "229 W 43rd Street, 5th FL", city: "New York", state: "NY", zip: "10036">]
Finished tests in 0.054955s, 36.3934 tests/s, 72.7868 assertions/s.
2 tests, 4 assertions, 0 failures, 0 errors, 0 skips

尝试查找未将ID存储为另一个类中的字段的类的所有实例

1 个答案: