MongoDB聚合，如何在组管道中添加数组的每个元素 [英] MongoDB aggregate, how to addToSet each element of array in group pipeline

问题描述

我有包含标签字段的文档.这是一个简单的数组，里面有标签名称，里面没有对象也没有 _id.像这样的普通标签 ["Protocol", "Access", "Leverage", "Capability"].

I have documents that contains a tags fields. It's a simple array with tag names inside, no object nor _id inside. Just plain tags like this ["Protocol", "Access", "Leverage", "Capability"].

在我的组管道中，我尝试了类似 'selectedTags': { $addToSet: '$tags' } 但最终得到一个包含标签数组的数组.$push 也一样.

And in my group pipeline I tried something like 'selectedTags': { $addToSet: '$tags' } but then I end up with an array containing arrays of tags. And I get the same with $push.

我尝试使用 $each 或 $pushAll 但不支持它们作为我的 shell 告诉我的分组运算符.

I tried to use $each or $pushAll but they are not supported as grouping operator as my shell tell me.

有人可以帮我解决这个问题吗?

Can someone help me on this one please ?

谢谢

示例文档:

{
    "_id" : "HWEdDGsq86x4ikDSQ",
    "teamId" : "AdLizGnPuqbWNsFHe",
    "ownerId" : "Qb5EigWjqn2t3bfxD",
    "type" : "meeting",
    "topic" : "Grass-roots hybrid knowledge user",
    "fullname" : "Guidouil",
    "startDate" : ISODate("2017-07-30T09:00:05.513Z"),
    "shareResults" : true,
    "open" : true,
    "language" : "fr",
    "tags" : [
        "Protocol",
        "Challenge",
        "Artificial Intelligence",
        "Capability"
    ],
    "isDemo" : true,
    "createdAt" : ISODate("2017-11-15T19:24:05.513Z"),
    "participantsCount" : 10,
    "ratersCount" : 10,
    "averageRating" : 3.4,
    "hasAnswers" : true,
    "updatedAt" : ISODate("2017-11-15T19:24:05.562Z")
}
{
    "_id" : "rXvkFndpXwJ6KAvNo",
    "teamId" : "AdLizGnPuqbWNsFHe",
    "ownerId" : "Qb5EigWjqn2t3bfxD",
    "type" : "meeting",
    "topic" : "Profit-focused modular system engine",
    "fullname" : "Guidouil",
    "startDate" : ISODate("2017-07-24T12:00:05.564Z"),
    "shareResults" : true,
    "open" : true,
    "language" : "fr",
    "tags" : [
        "Initiative",
        "Artificial Intelligence",
        "Protocol",
        "Utilisation"
    ],
    "isDemo" : true,
    "createdAt" : ISODate("2017-11-15T19:24:05.564Z"),
    "participantsCount" : 33,
    "ratersCount" : 33,
    "averageRating" : 2.9393939393939394,
    "hasAnswers" : true,
    "updatedAt" : ISODate("2017-11-15T19:24:05.753Z")
}

聚合:

db.surveys.aggregate(
  { $match: query },
  {
    $group: {
      '_id': {
        'year': { $year: '$startDate' },
        'day': { $dayOfYear: '$startDate' },
      },
      'participants': { $sum: '$ratersCount' },
      'rating': { $avg: '$averageRating' },
      'surveys': { $push: '$_id' },
      'selectedTags': { $addToSet: '$tags' },
      'peoples': { $addToSet: '$fullname' },
    }
  },
  { $sort: { _id: 1 } }
);

然后我尝试将 selectedTags 更改为 { $push: { $each: '$tags' } } 或 { $pushAll: '$tags' } 但是这不执行:(

then I tried to change the selectedTags to { $push: { $each: '$tags' } } or { $pushAll: '$tags' } but this does not execute :(

编辑 2:

在 javascript 中我是这样做的:

In javascript I do it like that:

return Surveys.aggregate(
  { $match: query },
  { $group: {
    _id: dateGroup,
    participants: { $sum: '$ratersCount' },
    rating: { $avg: '$averageRating' },
    surveys: { $push: '$_id' },
    selectedTags: { $push: '$tags' },
    peoples: { $addToSet: '$fullname' },
  } },
  { $project: {
    _id: null,
    selectedTags: {
      $reduce: {
        input: "$selectedTags",
        initialValue: [],
        in: { $setUnion: ["$$value", "$$this"] }
      }
    },
  } }
);

推荐答案

模仿$addToSet 更新运算符与 $each 修饰符 在聚合管道中，您可以使用 $push 在分组阶段和 $reduce + $setUnion 在投影阶段.例如:

To mimic functionality of $addToSet update operator with $each modifier in aggregation pipeline you can use a combination of $push on grouping stage and $reduce + $setUnion on projection stage. E.g.:

db.collection.aggregate([
    {$group:{
       _id: null,
       selectedTags: { $push: '$tags' }      
    }},
    {$project: {
        selectedTags: { $reduce: {
            input: "$selectedTags",
            initialValue: [],
            in: {$setUnion : ["$$value", "$$this"]}
        }}
    }}
])

结果为单个文档，该文档包含 selectedTags 数组中所有文档的不同标签列表.

results with a single document which contains a distinct list of tags from all documents in selectedTags array.

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