如何在数组的字段中进行 $lookup 并在同一查询中添加外部 table 的内容?

How to do $lookup in an array's field and add the foreign table's content in the same query?

我正在尝试进行查询,其中我有一个 db_task 查询,其中包含任务 ID 和分配给它的用户。我必须获取 db_user 集合中存在的用户详细信息,并将传入的详细信息添加到同一文档中。

db_task

{
    "_id" : ObjectId("5d8b522d0cf2579c57bc8ce0"),
    "users" : [ 
        {
            "user_id" : ObjectId("5d8b522d0cf2579e27bc8ce3"),
        "is_finished" : false
        }, 
        {
            "user_id" : ObjectId("5d6f6d25e079b9fb7d858236"),
            "is_finished" : false
        }
    ]
}

用户字段分配了该任务的用户,我想对 db_user 查询进行查找,这将使我获得同一嵌入式文档中的详细信息。

db_user

{
    "_id" : ObjectId("5d8b522d0cf2579e27bc8ce3"),
    "first_name" : "Harry",
    "last_name" : "Paul"
},

{
    "_id" : ObjectId("5d6f6d25e079b9fb7d858236"),
    "first_name" : "Aaron",
    "last_name" : "Potter"
}

我尝试使用 "users.user_id" 在 db_user table 上进行 $lookup,但这会为我获取一个新字段,然后我尝试将这些数组与“$concatArrays”连接起来但是结果还是不是我想的那样。

我想以类似这样的格式获得输出

db_task

{
    "_id" : ObjectId("5d8b522d0cf2579c57bc8ce0"),
    "users" : [ 
        {
            "user_id" : ObjectId("5d8b522d0cf2579e27bc8ce3"),
            "is_finished" : false,
            "user_info":{
                 "first_name" : "Harry",
                 "last_name" : "Paul"
              }
        }, 
        {
            "user_id" : ObjectId("5d6f6d25e079b9fb7d858236"),
            "is_finished" : false,
            "user_info":{
                  "first_name" : "Aaron",
                   "last_name" : "Potter"
              }
        }
    ]
}

它适合你。

 db_task.aggregate([
        {
            $match: { '_id': ObjectId("5d8b522d0cf2579c57bc8ce0") }
        },
        {
            $unwind: '$users'
        },
        {
            $lookup: {
                from: 'db_user',
                localField: 'users.user_id',
                foreignField: '_id',
                as: 'user_info'
            }
        },
        {
            $project: {
                $users: {
                    user_id: 1,
                    is_finished: 1,
                    user_info:'$user_info',
                }
            }
        },
        {
            $group: {
                _id: '$_id',
                users: {
                    $push: '$users'
                },
            }
        },
    ])

几乎与 vishal pankhaniya 解决方案相同,但我们从内部文档

中排除了 user_info._id
db.db_task.aggregate([
  {
    $unwind: "$users"
  },
  {
    $lookup: {
      from: "db_user",
      localField: "users.user_id",
      foreignField: "_id",
      as: "user_info"
    }
  },
  {
    $project: {
      users: {
        user_id: 1,
        is_finished: 1,
        user_info: "$user_info"
      }
    }
  },
  {
    $group: {
      _id: "$_id",
      users: {
        $push: "$users"
      }
    }
  },
  {
    $project: {
      "users.user_info._id": 0
    }
  }
])

结果


[
  {
    "_id": ObjectId("5d8b522d0cf2579c57bc8ce0"),
    "users": [
      {
        "is_finished": false,
        "user_id": ObjectId("5d8b522d0cf2579e27bc8ce3"),
        "user_info": [
          {
            "first_name": "Harry",
            "last_name": "Paul"
          }
        ]
      },
      {
        "is_finished": false,
        "user_id": ObjectId("5d6f6d25e079b9fb7d858236"),
        "user_info": [
          {
            "first_name": "Aaron",
            "last_name": "Potter"
          }
        ]
      }
    ]
  }
]

MongoPlayground

虽然他们在工作,但所提供的解决方案,包括放松和分组,在资源方面可能是昂贵的。 这里有一个更好的解决方案,只需要两个阶段:

db.db_task.aggregate([
  {
    $lookup: {
      from: "db_user",
      localField: "users.user_id",
      foreignField: "_id",
      as: "usersInfos"
    }
  },
  {
    $project: {
      users: {
        $map: {
          input: "$usersInfos",
          as: "ui",
          in: {
            $mergeObjects: [
              "$$ui",
              {
                $arrayElemAt: [
                  {
                    $filter: {
                      input: "$users",
                      as: "users",
                      cond: {
                        $eq: [
                          "$$users.user_id",
                          "$$ui._id"
                        ]
                      }
                    }
                  },
                  0
                ]
              }
            ]
          }
        }
      }
    }
  }
])

会输出

[
  {
    "_id": ObjectId("5d8b522d0cf2579c57bc8ce0"),
    "users": [
      {
        "_id": ObjectId("5d6f6d25e079b9fb7d858236"),
        "first_name": "Aaron",
        "is_finished": false,
        "last_name": "Potter",
        "user_id": ObjectId("5d6f6d25e079b9fb7d858236")
      },
      {
        "_id": ObjectId("5d8b522d0cf2579e27bc8ce3"),
        "first_name": "Harry",
        "is_finished": true,
        "last_name": "Paul",
        "user_id": ObjectId("5d8b522d0cf2579e27bc8ce3")
      }
    ]
  }
]

注意:根据@Valijon 的建议,如果您需要从此处稍微重新安排,您可以添加一个 $project 阶段。