MongoDb：管道内部查找错误：错误：参数必须是聚合管道运算符

Question

我有这三个模型：

1. Institution模特：

const InstitutionSchema = new Schema({
  current_students: [
    {
      type: Schema.Types.ObjectId,
      ref: "users",
    },
  ],
});

module.exports = Institution = mongoose.model("institutions", InstitutionSchema);

在current_students 字段中有对User 模型的引用数组。

1. User模特：

const UserSchema = new Schema({
  profile: {
    type: Schema.Types.ObjectId,
    ref: "profiles",
  },
});

module.exports = User = mongoose.model("users", UserSchema);

在profile 字段中引用了Profile 模型。

1. Profile模特：

const ProfileSchema = new Schema({
  videoURL: {
    type: String,
  },
});

module.exports = Profile = mongoose.model("profiles", ProfileSchema);

我正在尝试获取Profile.videoURL 不是null 或undefined 的机构用户的配置文件列表。这是我尝试过的：

Institution.aggregate([
  {
    $lookup: {
      from: "users",
      localField: "current_students",
      foreignField: "_id",
      as: "current_student",
    },
  },
  {
    $unwind: {
      path: "$current_student",
      preserveNullAndEmptyArrays: true,
    },
  },
  {
    $lookup: {
      from: "profiles",
      localField: "current_student.profile",
      foreignField: "_id",
      as: "current_student_profile",
    },
    pipeline: [
      {
        $match: {
          videoURL: { $nin: [undefined, null] },
        },
      },
    ],
  },
]);

但是，由于执行$match 操作的最后一个管道，我不断收到此错误。

Error: Arguments must be aggregate pipeline operators

知道如何解决这个问题吗？

Answer 1

您的查询是错误的。你不能像那样通过pipeline。看看$lookup 语法。另外，如果您想了解有关聚合的更多信息，我建议您使用 MongoDB 自己提供的 Aggregation course。对所有人免费。

试试这个查询：

db.institutions.aggregate([
    {
        $lookup: {
            from: "users",
            localField: "current_students",
            foreignField: "_id",
            as: "current_student",
        }
    },
    {
        $unwind: {
            path: "$current_student",
            preserveNullAndEmptyArrays: true,
        }
    },
    {
        $lookup: {
            from: "profiles",
            localField: "current_student.profile",
            foreignField: "_id",
            as: "current_student_profile",
        }
    },
    { $unwind: "$current_student_profile" },
    {
        $match: {
            "current_student_profile.videoURL": { $nin: [undefined, null] },
        }
    }
]);

输出：

/* 1 createdAt:3/13/2021, 6:18:26 PM*/
{
    "_id" : ObjectId("604cb49a6b2dcb17e8b152b2"),
    "name" : "Institute 1",
    "current_students" : [
        ObjectId("604cb4c36b2dcb17e8b152b8"),
        ObjectId("604cb4c36b2dcb17e8b152b9")
    ],
    "current_student" : {
        "_id" : ObjectId("604cb4c36b2dcb17e8b152b8"),
        "name" : "Dheemanth Bhat",
        "profile" : ObjectId("604cb4b16b2dcb17e8b152b5")
    },
    "current_student_profile" : {
        "_id" : ObjectId("604cb4b16b2dcb17e8b152b5"),
        "videoURL" : "http://abc1@xyz.com"
    }
},

/* 2 createdAt:3/13/2021, 6:18:26 PM*/
{
    "_id" : ObjectId("604cb49a6b2dcb17e8b152b3"),
    "name" : "Institute 2",
    "current_students" : [
        ObjectId("604cb4c36b2dcb17e8b152ba")
    ],
    "current_student" : {
        "_id" : ObjectId("604cb4c36b2dcb17e8b152ba"),
        "name" : "Alex Rider",
        "profile" : ObjectId("604cb4b16b2dcb17e8b152b7")
    },
    "current_student_profile" : {
        "_id" : ObjectId("604cb4b16b2dcb17e8b152b7"),
        "videoURL" : "http://abc3@xyz.com"
    }
}

测试数据：

users收藏：

/* 1 createdAt:3/13/2021, 6:19:07 PM*/
{
    "_id" : ObjectId("604cb4c36b2dcb17e8b152b8"),
    "name" : "Dheemanth Bhat",
    "profile" : ObjectId("604cb4b16b2dcb17e8b152b5")
},

/* 2 createdAt:3/13/2021, 6:19:07 PM*/
{
    "_id" : ObjectId("604cb4c36b2dcb17e8b152b9"),
    "name" : "Ahmed Ghrib",
    "profile" : ObjectId("604cb4b16b2dcb17e8b152b6")
},

/* 3 createdAt:3/13/2021, 6:19:07 PM*/
{
    "_id" : ObjectId("604cb4c36b2dcb17e8b152ba"),
    "name" : "Alex Rider",
    "profile" : ObjectId("604cb4b16b2dcb17e8b152b7")
}

profiles收藏：

/* 1 createdAt:3/13/2021, 6:18:49 PM*/
{
    "_id" : ObjectId("604cb4b16b2dcb17e8b152b5"),
    "videoURL" : "http://abc1@xyz.com"
},

/* 2 createdAt:3/13/2021, 6:18:49 PM*/
{
    "_id" : ObjectId("604cb4b16b2dcb17e8b152b6")
},

/* 3 createdAt:3/13/2021, 6:18:49 PM*/
{
    "_id" : ObjectId("604cb4b16b2dcb17e8b152b7"),
    "videoURL" : "http://abc3@xyz.com"
}

institutions收藏

/* 1 createdAt:3/13/2021, 6:18:26 PM*/
{
    "_id" : ObjectId("604cb49a6b2dcb17e8b152b2"),
    "name" : "Institute 1",
    "current_students" : [
        ObjectId("604cb4c36b2dcb17e8b152b8"),
        ObjectId("604cb4c36b2dcb17e8b152b9")
    ]
},

/* 2 createdAt:3/13/2021, 6:18:26 PM*/
{
    "_id" : ObjectId("604cb49a6b2dcb17e8b152b3"),
    "name" : "Institute 2",
    "current_students" : [
        ObjectId("604cb4c36b2dcb17e8b152ba")
    ]
}

Answer 2

必须是这样的：

Institution.aggregate([
  {
    $lookup: {
      from: "users",
      localField: "current_students",
      foreignField: "_id",
      as: "current_student",
    },
  },
  {
    $unwind: {
      path: "$current_student",
      preserveNullAndEmptyArrays: true,
    },
  },
  {
    $lookup: {
      from: "profiles",
      localField: "current_student.profile",
      foreignField: "_id",
      as: "current_student_profile",
    }
   },
   {
     $match: {
       videoURL: { $nin: [undefined, null] },
     },
   }
]);

注意，这看起来像是关系 RDBMS 设计的“一对一”转换。通常它不是将每个表格转换为集合的最佳方法，通常集合应该有不同的设计。