javascript - 我在 mongodb 聚合中使用查找，但它不返回我正在查找的数据

Question

这是一个示例建筑集合。

{
    _id: 5e4aa096a6b7db2270c65815,
    previous_audit: false,
    no_of_people: 3,
    project_name: 'UNDP',
    premise_contact: 'Kanagaraj',
    premise_address: 'Delhi',
    premise_city: 'Delhi',
    premise_state: 'Delhi',
    premise_country: 'IN',
    latitude: '28.593716',
    longitude: '77.222391',
    building_name: 'Nemi',
    building_type: 'Hospital',
    climate_zone: 'Hot & Dry',
    no_of_stories: '3',
    year_of_occupation: 3,
    gross_area: 3333,
    gross_area_units: 'Square Meters',
    lease_type: 'Annual Rental',
    campus_id: 5e4857816560b92a58129e68,
    project_name_lower: 'undp',
    createdAt: 2020-02-17T14:17:58.892Z,
    updatedAt: 2020-02-17T14:17:58.892Z,
    __v: 0,
}

在第一个管道阶段，我使用 $match 函数。

Building.aggregate([
    {
        $match: {
            campus_id: {
                $in: campus_ids
            }
        }
    },
    {
        $lookup: {
            from: 'manual_meters',
            localField: '_id',
            foreignField: 'building_name',
            as: 'manual_meter'
        }
    }
])

但是当查找lookup时，它总是在manual_meter中返回空数组。这就是我得到的答复。虽然采集手动电表中包含了建筑物的id，但仍然没有返回手动电表采集。

 {
    _id: 5e4857816560b92a58129e72,
    previous_audit: false,
    project_name: 'UNDP',
    premise_contact: 'Kanagaraj',
    premise_address: 'Delhi',
    premise_city: 'Delhi',
    premise_state: 'Delhi',
    premise_country: 'IN',
    latitude: '28.593716',
    longitude: '77.222391',
    building_name: 'U.N.House',
    building_type: 'Office',
    climate_zone: 'Hot & Dry',
    no_of_stories: '4',
    year_of_occupation: 1970,
    gross_area: 6500,
    gross_area_units: 'Square Meters',
    lease_type: 'Owned',
    campus_id: 5e4857816560b92a58129e68,
    project_name_lower: 'undp',
    createdAt: 2020-02-15T20:41:37.171Z,
    updatedAt: 2020-02-15T20:41:37.171Z,
    __v: 0,
    manual_meter: []
  },
  {
    _id: 5e4aa096a6b7db2270c65815,
    previous_audit: false,
    no_of_people: 3,
    project_name: 'UNDP',
    premise_contact: 'Kanagaraj',
    premise_address: 'Delhi',
    premise_city: 'Delhi',
    premise_state: 'Delhi',
    premise_country: 'IN',
    latitude: '28.593716',
    longitude: '77.222391',
    building_name: 'Nemi',
    building_type: 'Hospital',
    climate_zone: 'Hot & Dry',
    no_of_stories: '3',
    year_of_occupation: 3,
    gross_area: 3333,
    gross_area_units: 'Square Meters',
    lease_type: 'Annual Rental',
    campus_id: 5e4857816560b92a58129e68,
    project_name_lower: 'undp',
    createdAt: 2020-02-17T14:17:58.892Z,
    updatedAt: 2020-02-17T14:17:58.892Z,
    __v: 0,
    manual_meter: []
  }
]

下面是一个样本manual_meter集合。

    {"_id":"5e4ad8e1a3833e2bb44b4dcb",
"meter_data : [],
"meter_name":"undp_unh",
"meter_id":"1001",
"meter_type":"energy",
"campus_name":"UNDP",
"building_name":"5e4857816560b92a58129e72",
"floor_name":"common",
"zone_name":"common",
"createdAt":"2020-02-17T18:18:09.192Z",
"updatedAt":"2020-02-17T18:18:09.192Z",
"__v":0}

Answer 1

看起来您正在尝试将 string 与 ObjectId 进行匹配，即使值相同，这也不起作用。您可以运行$toString作为 $lookup 的一部分在您的 _id 字段上:

{
    $lookup: {
        from: "manual_meters",
        let: { building_id: { $toString: "$_id" } },
        pipeline: [
            {
                $match:{
                    $expr: {
                        $eq: [ "$$building_id", "$building_name" ]
                    }
                }
            }
        ],
        as: "manual_meter"
    }
}