MongoDb 聚合 $lookup 和 $project

Question

我刚刚遇到了一个有趣的聚合管道问题。因为我是新手，所以我随机尝试了一些东西，但没有得到想要的输出。希望大家帮我解决！

我有两个collection，

collection一个=>

{
    _id: 1,
    field1: "value1",
    field2: "value2
}

collection b=>

{
    _id: 101,
    collectionAId: 1,
    status: "active"
},
{
    _id: 102,
    collectionAId: 1,
    status: "inactive"
},
{
    _id: 102,
    collectionAId: 1,
    status: "expired"
}

我的目标是

{
    _id: 1,
    field1: "value1",
    field2: "value2,
    status: ["active", "inactive", "expired"]
}

Answer 1

您可以使用 $map 结合 $project:

来实现

db.a.aggregate([
  {
    "$lookup": {
      "from": "b",
      "localField": "_id",
      "foreignField": "collectionAId",
      "as": "output"
    }
  },
  {
    "$project": {
      field1: 1,
      field2: 1,
      status: {
        "$map": {
          "input": "$output",
          "as": "v",
          "in": "$$v.status"
        }
      }
    }
  }
])

MongoDb 聚合 $lookup 和 $project

MongoDb aggregation $lookup and $project

aggregation

mongodb

aggregation-framework