Question

我正在使用聚合来加入3个收藏集。但是联接的结果是一个空的array []。这是我所有3个集合的模型，以及汇总查询。 console.log（timetable）的结果返回[]。我使用引用来引用时间表中具有相应集合的字段。

时间表模型

var TimetableSchema = new mongoose.Schema ({

    timeslot: {
        required: true, 
        'type': String,
    },

    classroom :{
        type: mongoose.Schema.Types.ObjectId,
        ref: 'Classroom'
    },

    subject :{
        type: mongoose.Schema.Types.ObjectId,
        ref: 'Subject'
    },

    teacher :{
        type: mongoose.Schema.Types.ObjectId,
        ref: 'User'   
    },

    day :{
        type:String, 
        required: true, 
    },

    year :{
        type:String, 
        required: true, 
    },

    session :{
        type:String,
        required:true,
    }


})

教室模式

var ClassroomSchema = new mongoose.Schema ({


    classroom_name: {
        type:String,
        required:true,
        unique: true,
    },

    classroom_blok:{
        type:String,
        required:true,
    },

    classroom_floor: {
        type:String,
        required:true,
    },


});

主题

var SubjectSchema = new mongoose.Schema ({

    subject_id: {

        required: true, 
        'type': String,
        'default': shortid.generate
    },

    subject_name: {
        type:String,
        required:true,
    },

    subject_darjah:{
        type:String,
        required:true,
    }

});

汇总查询

router.get('/today_absentee/view/:id',function(req,res){
  Teacher.findById(req.session.userId).exec(function (error, user){
    if (error){
      return next(error);
    }else
    {
      Teacher.find({_id:req.params.id }).exec(function(err, teacher){
        if(err)
        {
          return next(err);
        }else
        {
          Timetable.aggregate([

            {
                // This is doing the same thing as the previous .find()
               $match: {  teacher:req.params.id}
            },
            {
              $lookup:{
                  from: "Classroom",       // other table name
                  localField: "classroom",   // name of users table field
                  foreignField: "_id", // name of userinfo table field
                  as: "classroom"         // alias for userinfo table
              }



            },

            {   $unwind:"$classroom" },     // $unwind used for getting data in object or for one record only

            {
              $lookup:{
                  from: "Subject",       // other table name
                  localField: "subject",   // name of users table field
                  foreignField: "_id", // name of userinfo table field
                  as: "subject"         // alias for userinfo table
              }  
            },

            {   $unwind:"$subject" },     // $unwind used for getting data in object or for one record only

            // define some conditions here 
            {
                $match:{
                $and:[{teacher:req.params.id}]
                 }
            },

            // define which fields are you want to fetch
             {   
                $project:{

                    subject_name : "$subject.subject_name",
                    classroom : "$classroom.classroom_name",
                } 
             }
          ]).exec(function(err, timetable) 
          {
            // The query output is such that `classroom.classroom_name`
            // value is unique for each document
            if (err) throw err;
            console.log(currentYear);
            console.log(timetable);
            res.render('creator_content/today_absentee_id',{timetable:timetable,  user:user, teacher:teacher});
          });
        }
      });


    }
  });
});

所有3个模型的模型。

Answer 1

在文件顶部导入 mongoose ，然后在与聚合查询中的任何对象ID字段匹配时使用 mongoose.Types.ObjectId（）。我还使用了 $ addFields 聚合管道来添加2个字段（subject_name，教室），然后在下一个阶段使用 $ project 输出它们。

$2

猫鼬：汇总返回空值

1 个答案: