mongoId 对 activerecord 的 any_of 实现问题

Question

我有这样的设置模型数据

[52] pry(main)> Setting.all.to_a
    => [#<Setting _id: 561cc75b25917fdc2300003c, courses: ["521c4578ef8b6038ba000069", "55f909c825917f1ac000003e"], user_id: "55f908d725917f5157000036">,
     #<Setting _id: 563b322425917f8117000025, courses: ["561cddbb25917fa26e0000b9", "5614e62225917fbb1300005f", "5617a6bd25917f7aa100005d", "560ca6b325917f158d000002", "5617a5f325917ff38c000036", "5632eebc25917f1ace000038", "55f909c825917f1ac000003e", "521c4578ef8b6038ba000069"], user_id: "56125d7b25917fb8c0000001">,
     #<Setting _id: 5641d3b125917fa02f000009, courses: ["5614e62225917fbb1300005f", "55f909c825917f1ac000003e", "521c4578ef8b6038ba000069"], user_id: "5264b629ef8b604f96000001">,
     #<Setting _id: 565d541925917f10da000013, courses: ["561cddbb25917fa26e0000b9", "5614e62225917fbb1300005f", "5617a6bd25917f7aa100005d", "5617a5f325917ff38c000036", "560ca6b325917f158d000002", "55f909c825917f1ac000003e", "5632eebc25917f1ace000038", "521c4578ef8b6038ba000069"], user_id: "565d53f525917f10da000012">]

现在我想要一组具有特定课程的设置

    pry(main)> course = Course.find("5614e62225917fbb1300005f")
    pry(main)> Setting.any_of(courses: course.id).to_a
=> [#<Setting _id: 565d541925917f10da000013, courses: ["561cddbb25917fa26e0000b9", "5614e62225917fbb1300005f", "5617a6bd25917f7aa100005d", "5617a5f325917ff38c000036", "560ca6b325917f158d000002", "55f909c825917f1ac000003e", "5632eebc25917f1ace000038", "521c4578ef8b6038ba000069"], user_id: "565d53f525917f10da000012">]

它只产生了一个不是预期结果的数组元素，然后

[53] pry(main)> Setting.any_of(courses: course.id.to_s).to_a
=> [#<Setting _id: 563b322425917f8117000025, courses: ["561cddbb25917fa26e0000b9", "5614e62225917fbb1300005f", "5617a6bd25917f7aa100005d", "560ca6b325917f158d000002", "5617a5f325917ff38c000036", "5632eebc25917f1ace000038", "55f909c825917f1ac000003e", "521c4578ef8b6038ba000069"], user_id: "56125d7b25917fb8c0000001">,
 #<Setting _id: 5641d3b125917fa02f000009, courses: ["5614e62225917fbb1300005f", "55f909c825917f1ac000003e", "521c4578ef8b6038ba000069"], user_id: "5264b629ef8b604f96000001">]

产生两个数组元素，但期望的结果是三个数组元素，可以通过将这两个结果相加或通过以下语法来获得

[57] pry(main)> Setting.any_of({courses: course.id.to_s}, {courses: course.id}).to_a
=> [#<Setting _id: 563b322425917f8117000025, courses: ["561cddbb25917fa26e0000b9", "5614e62225917fbb1300005f", "5617a6bd25917f7aa100005d", "560ca6b325917f158d000002", "5617a5f325917ff38c000036", "5632eebc25917f1ace000038", "55f909c825917f1ac000003e", "521c4578ef8b6038ba000069"], user_id: "56125d7b25917fb8c0000001">,
 #<Setting _id: 5641d3b125917fa02f000009, courses: ["5614e62225917fbb1300005f", "55f909c825917f1ac000003e", "521c4578ef8b6038ba000069"], user_id: "5264b629ef8b604f96000001">,
 #<Setting _id: 565d541925917f10da000013, courses: ["561cddbb25917fa26e0000b9", "5614e62225917fbb1300005f", "5617a6bd25917f7aa100005d", "5617a5f325917ff38c000036", "560ca6b325917f158d000002", "55f909c825917f1ac000003e", "5632eebc25917f1ace000038", "521c4578ef8b6038ba000069"], user_id: "565d53f525917f10da000012">]

我的困惑是为什么

Setting.any_of(courses: course.id).to_a

和

Setting.any_of(courses: course.id.to_s).to_a

产生不同的结果，我的第三种语法方法是获得我想要的结果的唯一正确方法吗？

Answer 1

我不能 100% 确定，因为我真的不知道您的数据库中有什么。不过，我对这里的问题很有信心。

由于您没有分享您的设置模型定义，我猜想是这样的：

class Setting
  include Mongoid::Document
  field :courses, type: Array
end

如果这不正确，请告诉我，我会更新答案。鉴于这种结构，看看这个撬动会话：

[4] pry(main)> string_id = "563b322425917f8117000025"   
=> "563b322425917f8117000025"
[5] pry(main)> object_id = Moped::BSON::ObjectId.from_string("563b322425917f8117000025")   
=> "563b322425917f8117000025"
[6] pry(main)> string_id.class.name   
=> "String"
[7] pry(main)> object_id.class.name   
=> "Moped::BSON::ObjectId"

请注意Moped::BSON::ObjectId 适用于 Mongoid 3（我碰巧在这里安装的那个）。在较新的版本中，它只是 BSON::ObjectId，因为 Mongoid 4+ 放弃了 Moped gem。

我们可以创建两个不同的对象来表示同一个标识符。一个是 String 实例，另一个是 Moped::BSON::ObjectId 类，在 Mongoid 内部用于表示同一事物，即 Mongo ObejctId。

为了让事情变得更简单，Mongoid（和 mongo 本身）允许您在某些情况下使用字符串而不是 ObjectId，但并非总是如此。在某些情况下，与上述 Setting 类一样，它无法知道您是否要将 String 实例或 ObjectId 实例保存到数据库中。因此，它将保存您发送到的任何内容：

[10] pry(main)> st = Setting.new(:courses => [object_id])
=> #<Setting _id: 5694ff9a04572eeb16000001, courses: ["563b322425917f8117000025"]>
[11] pry(main)> st.save
=> true
[12] pry(main)> st2 = Setting.new(:courses => [string_id])
=> #<Setting _id: 5694ffa904572eeb16000002, courses: ["563b322425917f8117000025"]>
[13] pry(main)> st2.save
=> true
[14] pry(main)> Setting.where(:courses => string_id).to_a
=> [#<Setting _id: 5694ffa904572eeb16000002, courses: ["563b322425917f8117000025"]>]
[15] pry(main)> Setting.where(:courses => string_id).to_a == [st2]
=> true
[17] pry(main)> Setting.where(:courses => object_id).to_a == [st]
=> true

因此，变量st 指向一个Setting 对象，该对象保存有一个包含一个ID 的课程字段，表示为Moped::BSON::ObjectId 实例，而st2 包含相同ID 的纯字符串表示。所以，这两件事看起来是一样的，而且很难发现，因为 Moped::BSON::ObjectID#to_s 方法返回的 id 与 String#to_s 完全相同，所以如果你尝试将它打印到 shell 会话中，你将无法发现差异.要发现差异，您必须致电 object_id.class.name 并与 string_id.class.name 进行比较。

您可以通过运行以下命令来证明您是否属于这种情况：

all_settings = Setting.any_of({courses: course.id.to_s}, {courses: course.id})
all_settings.each do |a_setting|
  puts "Setting #{a_setting.id}:"

  a_setting.courses.each do |string_or_object_id|
    puts "   #{string_or_object_id.class.name} #{string_or_object_id}"
  end
end

理想情况下，您应该在此数组中仅使用 String 对象或仅使用 ObjectId 对象，否则您将来会遇到问题。要解决这个问题。我建议您使用Moped::BSON::ObjectId，因为它映射到自然的 ObjectId Mongo 表示，并允许您做一些有趣的事情，例如按生成日期查询 ObjectId：

[21] pry(main)> object_id.generation_time
=> 2015-11-05 10:40:36 UTC

我希望这会有所帮助:)