MongoDB从基础添加到加入集合字段 [英] MongoDB add to joining collection field from base one

问题描述

我有两个收藏:

带有架构的游戏:

 _id: ObjectId('gameId'),
 questions: [
   {
     position: 1,
     question_id: ObjectId('baz')
   },
   {
     position: 2,
     question_id: ObjectId('ban')
   },
 ]

架构问题:

 _id: ObjectId('baz'),
 text: 'FooBar'

现在我想将问题加入到游戏中，并添加到 question_position 的每个问题记录值.

And now I'd like to join questions to games with adding to each question record value of question_position.

所以，我有这样的查询:

So, I have query like this:

db.games.aggregate([
    {
      $lookup: {
        from: 'questions',       
        localField: 'questions.question_id',
        foreignField: '_id',       
        as: 'question_data',     
      },   
     }])

返回所有必需的信息，并根据问题数组正确连接，

Which return me all required info, with correct join according to questions array,

 _id: ObjectId('gameId'),
 questions: [
   {
     position: 1,
     question_id: ObjectId('baz')
   },
   {
     position: 2,
     question_id: ObjectId('ban')
   }
 ],
 question_data: [
   {
     _id: ObjectId('baz'),
     text: 'FooBar',
   },
   {
     _id: ObjectId('ban'),
     text: 'FooBar2',
   }
 ]

但我完全不知道如何根据游戏将其位置添加到连接问题中.看起来像这样:

but I'm totally can't figure out how to add into joined questions it's position according to game. To look it like this:

 _id: ObjectId('gameId'),
 questions: [
   {
     position: 1,
     question_id: ObjectId('baz')
   },
   {
     position: 2,
     question_id: ObjectId('ban')
   }
 ],
 question_data: [
   {
     _id: ObjectId('baz'),
     text: 'FooBar',
     position: 1,
   },
   {
     _id: ObjectId('ban'),
     text: 'FooBar2',
     position: 2,
   }
 ]

我已经尝试使用 $unwind 作为游戏集合中的问题数组，在 aggregation 中使用 $project 玩了一下，但仍然没有结果.

I've tried with $unwind for question array in game collection, played a little with $project in aggregation but still no result.

所以，我的问题是，如何将基础集合中的字段添加到另一个集合中的连接数据中

So, my question is, how to add field from base collection to joined data from another collection

推荐答案

你需要先$unwind questions 数组，然后需要应用 $lookup 最后使用 $group 回滚再次进入数组.

You need to first $unwind the questions array and then need to apply $lookup and finally use $group to rollback again into the array.

db.games.aggregate([
  { "$unwind": "$questions" },
  { "$lookup": {
    "from": "questions",
    "localField": "questions.question_id",
    "foreignField": "_id",
    "as": "question_data"
  }},
  { "$unwind": "$question_data" },
  { "$addFields": {
    "question_data.position": "$questions.position",
    "question_data.question_id": "$questions.question_id"
  }},
  { "$group": {
    "_id": "$_id",
    "questions": { "$push": "$questions" },
    "question_data": { "$push": "$question_data" }
  }}
])

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