Mongoose: Model.aggregate returning an empty array

Question

I'm trying to calculate an average value based on the user's rating for the product.

My Schemas:

const journalSchema = new mongoose.Schema({
  title: String,
  category: String,
  subcategory: String,
  review: [{type: mongoose.Schema.Types.ObjectId, ref: 'Review'}],
  link: String,
  description: String,
  subscribers: Number,
  image: String
});

const reviewSchema  = new mongoose.Schema({
  author: {type: mongoose.Schema.Types.String, ref: 'User'},
  content: String,
  date: Date,
  rating: {type: Number, min: 1.0, max: 5.0}
});

const Journal = mongoose.model("Journal", journalSchema);
const Review = mongoose.model("Review", reviewSchema);

Route:

app.get("/", function(req, res){
Journal.find({}, function(err, journals){
  if(err){
    console.log(err);
  }
  else{
      Review.aggregate([
        {$unwind: "$journals"},
        {$match: {_id: {$in: journals}}},
        {$unwind: "$journals.review"},
        {$group: {_id: journals.review, average: {$avg: "$rating"}}}
      ], function(err, results){
        if(err){
          console.log(err);
        }
        else{
          console.log(results);
        }
      })
    res.render("home", {journals: journals});
    }
  });
});

All I get is an empty array.

My goal is to render the page with shops that have a rating above 4. I can't figure out where the issue is. Is it possible to achieve this with other alternatives or using aggregate is the way to go?

turivishal · Accepted Answer · 2021-08-16 16:18:28Z

1

You can use the aggregation method,

$lookup with reviews collection
$avg to get average of rating from reviews result
$match to filter journals by rating should greater than 4

app.get("/", function(req, res) {
  Journal.aggregate([
    {
      $lookup: {
        from: "reviews",
        localField: "review",
        foreignField: "_id",
        as: "review"
      }
    },
    {
      $addFields: { review: { $avg: "$review.rating" } }
    },
    {
      $match: {
        review: { $gt: 4 }
      }
    }
  ], 
  function(err, results) {
    if(err) { console.log(err); }
    else { 
      res.render("home", { journals: results });
    }
  })
});

Playground

edited Aug 16, 2021 at 16:18

answered Aug 16, 2021 at 15:47

turivishal

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5 Comments

indee423 Over a year ago

Still getting an empty array :(

turivishal Over a year ago

make sure the conneted database is correct and collection name reviews is correct. debug step by step, by removing stages from pipeline, otherwise we can't help by just this information Still getting an empty array

indee423 Over a year ago

I have another schema for users which I referenced in the review schema to get the user's username, is it possible that it might be causing the problem?

turivishal Over a year ago

no, you just need to debug query, 1) try by just no pipeline stage Journal.aggregate([] 2) try by first $lookup stage etc.

indee423 Over a year ago

So I removed the $match part, and instead checked the average in the ejs file and now it works, not sure if it's a good way to do it

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