MongoDB：$lookup 后嵌套文档上的 $match

Question

I need to query a collection of timecards which are linked to jobs, while jobs are linked to facilities with a specific facility ID. I have the following aggregation query:

Timecard.aggregate([
    { $match: query }, //some query parameters set before, doesn't matter here
    {
        $lookup: {
            from: 'jobs',
            as: 'job',
            localField: 'job',
            foreignField: '_id'
        }
    },
    { $unwind: '$job' },
    {
        $lookup: {
            from: 'facilities',
            localField: 'job.facilityId'
            foreignField: '_id',
            as: 'job.facilityId'
        }
    },
    { $unwind: '$job.facilityId' },
    { $match: {'job.facilityId._id':'5cad048d95d61a002f5a9edb'}}
];)

Everything before the last $match works just fine, jobs are populated into timecards, facilities are populated into jobs. But the match doesn't work for some reason. However, if I add facilityId field with

{$addFields: {facilityId: '$job.facilityId._id'}}

and change the $match to

{$match: 'facilityId':'5cad048d95d61a002f5a9edb'}

then it works. The question is, is there a way to query a subdocument's field with dot notation this way?

Answer 1

您的最后一行可能需要是 ObjectId

{ $match: {'job.facilityId._id': ObjectId('5cad048d95d61a002f5a9edb')}}