NodeJS, MongoDB, Aggregation function with $lookup result is empty array []

Question

my grades model is:

var mongoose = require("mongoose");
var Schema = mongoose.Schema;

var GradeSchema = new Schema({
gID: {type:Schema.Types.ObjectId,ref: 'People'},
    grade: Number,
    type: Number
}, {timestamps: true});

var Grade = mongoose.model('Grade', GradeSchema);
module.exports=Grade;

people model is:

var mongoose = require("mongoose");
var Schema = mongoose.Schema;

var PeopleSchema = new Schema({
_id: {type:Schema.Types.ObjectId,ref:'Grade' },
    name: String,
    lastName:String,
    phone: String
},{timestamps: true});

var People = mongoose.model('People', PeopleSchema);

module.exports=People;

my aggregate query is:

Grade.aggregate([

      {$lookup:{ from: 'People', localField:'glD', 
        foreignField:'_id',as:'myCustomResut'}},
]).exec((err, result)=>{
      if (err) {
          console.log("error" ,err)
      }
      if (result) {
          console.log(result);
      }
});

** but myCustomResut is empty result like myCustomResut []: ** what is wrong with this code?

[ { _id: 5a13e33e931f7561b85d0840, updatedAt: 2017-11-21T08:26:38.413Z, createdAt: 2017-11-21T08:26:38.413Z, gID: 5a13e33e931f7561b85d083f, grade: 20, type: 2, __v: 0, myCustomResut:: [] }, { _id: 5a13e78e4fac5b61ecdbd9ab, updatedAt: 2017-11-21T08:45:02.517Z, createdAt: 2017-11-21T08:45:02.517Z, gID: 5a13e78e4fac5b61ecdbd9aa, grade: 20, type: 2, __v: 0, myCustomResut:: [] } ]

did u find answer

Nahid Hasan
– Nahid Hasan

2017-11-28 06:41:45 +00:00
Commented Nov 28, 2017 at 6:41 — Nahid Hasan
– Nahid Hasan, Commented Nov 28, 2017 at 6:41

Alex P. · Accepted Answer · 2017-11-22 21:18:48Z

4

Check if your collection is really People. From experience I know that people created a collection with capital letter but in their database it was with small. So check if it is not people instead. It has to do with Mongoose. So try your aggregation again like that:

Grade.aggregate([

      {$lookup:{ from: 'people', localField:'gID', 
        foreignField:'_id',as:'myCustomResut'}},
]).exec((err, result)=>{
      if (err) {
          console.log("error" ,err)
      }
      if (result) {
          console.log(result);
      }
});

Here you defined your field gID (upper case i):

var GradeSchema = new Schema({ gID: {type:Schema.Types.ObjectId,ref: 'People'}

And here you wrote glD (lower case L):

{$lookup:{ from: 'People', localField:'glD'

I updated the code snippet above, so try again, with the collection as People or people. But the mistake is definitely the glD. It was also tricky for me to see, because if you read the code like that, it doesn't look like there is a problem. I only realized it's wrong when I went to edit my answer.

edited Nov 22, 2017 at 21:18

answered Nov 22, 2017 at 18:45

Alex P.

3,1813 gold badges28 silver badges34 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Fazel Najariyan Over a year ago

test it by other names but result is myCustomResut[]

Fazel Najariyan Over a year ago

thank you my problem solve whene use {$lookup:{ from: 'people', localField:'glD'

Alex P. Over a year ago

@FazelNajariyan if your question was answered. Could you please also mark it as answered?

Cleyton T. Over a year ago

I have the same issue but I'm not using Mongoose. If I run a query in the Mongodb console it works fine but the same query in NodeJS using the latest version of the 'mongodb' package produces an empty result. Any ideas?

Ahmed Ibrahim Over a year ago

@CleytonT. I'm also having the same issue you had.

Rohit Mankotia · Accepted Answer · 2021-04-22 06:38:53Z

0

try to write collection name peoples instead of people

 Grade.aggregate([

      {$lookup:{ from: 'peoples', localField:'gID', 
        foreignField:'_id',as:'myCustomResut'}},
]).exec((err, result)=>{
      if (err) {
          console.log("error" ,err)
      }
      if (result) {
          console.log(result);
      }
});

answered Apr 22, 2021 at 6:38

Rohit Mankotia

11 bronze badge

Collectives™ on Stack Overflow

NodeJS, MongoDB, Aggregation function with $lookup result is empty array []

2 Answers 2

5 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related