在 $unwind 之前检查子文档是否不为空

我有一个Job包含 job_title、job_location、salary 等的 schema

应用架构将子文档嵌入到工作文档中，它存储该特定工作已收到的所有申请

这是作业架构的样子

const jobSchema = new Schema({
  job_title : {
    type : String,
    required : true
  },
  job_location : {
    type : String,
  },
  salary : {
    type : Number
  },
  applications: [ApplicationSchema],
  companyId : {
    type: mongoose.Schema.Types.ObjectId,
    ref: 'Company'
  }
},{timestamps : true});

var Job = mongoose.model('Job', jobSchema);

module.exports = Job;

您可以看到上面的应用程序子文档。

这是当没有特定工作申请时我的工作文档的样子

 {
"_id" : ObjectId("5ac873c3bb7a9c3168ff159e"),
    "applications" : [],
    "job_title" : "Junior Developer",
    "companyId" : ObjectId("5ac870d0bb7a9c3168ff159c"),
    "createdAt" : ISODate("2018-04-07T07:31:15.257Z"),
    "updatedAt" : ISODate("2018-04-07T09:20:52.237Z"),
    "__v" : 2,
    "job_location" : "Pune, Maharashtra, India",
    "salary" : 3
}

并与应用程序

   {
    "_id" : ObjectId("5ac873c3bb7a9c3168ff159e"),
        "applications" : [ 
            {
                "applied" : true,
                "shortlisted" : false,
                "interviewed" : false,
                "offered" : false,
                "hired" : false,
                "rejected" : false,
                "rejectedComment" : ""
            }, 
            {
                "applied" : true,
                "shortlisted" : false,
                "interviewed" : false,
                "offered" : false,
                "hired" : false,
                "rejected" : false,
                "rejectedComment" : ""
            }
        ],
        "job_title" : "Junior Developer",
        "companyId" : ObjectId("5ac870d0bb7a9c3168ff159c"),
        "createdAt" : ISODate("2018-04-07T07:31:15.257Z"),
        "updatedAt" : ISODate("2018-04-07T09:20:52.237Z"),
        "__v" : 2,
        "job_location" : "Pune, Maharashtra, India",
        "salary" : 3
    }

这是查询

var jobsQuery = [
      {
        $match: {
          companyId: mongoose.Types.ObjectId(req.body.companyId),
          active: req.body.active
        }
      },
      {
        $unwind: "$applications"
      },
      {
        $match : query
      },
      {
        "$group":
                {
                  "_id": "$job_title",
                  "job_title": {$first: "$_id"},
                  "job_location": {$first: "$job_location"},
                  "min_experience": {$first: "$min_experience"},
                  "max_experience": {$first: "$max_experience"},
                  "min_salary": {$first: "$min_salary"},
                  "max_salary": {$first: "$max_salary"},
                  "createdAt": {$first: "$createdAt"},
                  "userId": {$first: "$userId"},

                  "applied": {"$sum":
                                   {"$cond":
                                           [{"$and": [
                                             {"$eq":["$applications.applied", true]},
                                             {"$eq":["$applications.shortlisted", false]},
                                             {"$eq":["$applications.interviewed", false]},
                                             {"$eq":["$applications.offered", false]},
                                             {"$eq":["$applications.hired", false]},
                                             {"$eq":["$applications.rejected", false]},
                                           ]},
                                           1,0]
                                   }
                             },

                }
      },
      {
          "$lookup":
              {
                  from: "users",
                  localField: "userId",
                  foreignField: "_id",
                  as: "userDetail"
              }
      },
    ]

当一份工作收到申请时，它工作得很好，但当没有收到申请时，它就无法放松，这就是我什么也得不到的地方

那么我怎样才能给出一些条件，以便这个查询在有或没有任何应用程序的情况下都可以工作

我也在查询申请阶段的申请人数，我也有其他阶段。

你需要添加preserveNullAndEmptyArrays你里面的财产$unwind像这样的操作：

{
 $unwind:
  {
    path: "$applications",
    preserveNullAndEmptyArrays: true
  }
}

如果为 true，并且路径为 null、缺失或为空数组，则 $unwind 输出文档。如果为 false，则当路径为空、缺失或空数组时，$unwind 不会输出文档。

$unwind