Mongoose populate sort option

Question

I am trying to sort a populated document by the populated fields, similar to the example in the mongoose docs:

http://mongoosejs.com/docs/api.html#query_Query-populate

Where Kitten references owner by objectId and a query on Kitten is able to be sorted by the owner name. I've tried numerous variations of the syntax, such as from the answers given in

How to sort a populated document in find request?

While all of them populate and do not throw any errors, the sort option is not working for me. The one solution I have not tried yet is given here:

Mongoose, sort based on foreign/populated key

But does not use the available functionality of populate from mongoose and feels like a work around. Maybe a pair of fresh eyes could point out my problem.

My models (Semester and SemesterReference):

var semesterSchema = mongoose.Schema({
  year: Number,
  season: {
type: String,
enum: ["FALL", "SPRING", "SUMMER"]
  }
});

var semesterReferenceSchema = mongoose.Schema({
  name: String,
  semester: {type: mongoose.Schema.Types.ObjectId, ref:"Semester"}
});

Result when I query with this code

schema.SemesterReference.find().populate({path: "semester", options: {sort: {"year": 1}}}).exec().then(function(result){
console.log(result);
})

[ { _id: 5b2bb2312731613ba06b0e8f,
name: 'ZZZ',
semester:
 { _id: 5b23bd1e0ffe9a29d02ee02c,
   year: 2019,
   season: 'SPRING',
   __v: 0 },
__v: 0 },
{ _id: 5b2bb24b3c19bd1f3c1b0d66,
name: 'AAA',
semester:
 { _id: 5b23bd1e0ffe9a29d02ee011,
   year: 2010,
   season: 'SPRING',
   __v: 0 },
__v: 0 } ]

The query returns the same result as if I had not specified sorting by year in options at all. I have tried the same query without quotes around semester or year, which does not work either. Worryingly, changing "year" in the query above to a string that does not match a property of semester (such as asdf) does not throw any errors and the query returns as normal, which seems to indicate that the sort option is being ignored.

I am on version 5.1.6 of mongoose and 3.6.0 of mongodb.

your query returns year in ascending order... what is the problem here? — Ashh
Sort: 1 means sorting in ascending order, my query is returning them in the order they were saved to the database (the incorrect order, which also happens to be descending; 2019 before 2010 is descending order). — Quincy
Well you are using latest version of mongoose and mongodb, So do you want to try something different? I mean $lookup — Ashh
I'll use lookup for now, from the answer I linked above: sort based on foreign populate key, just to get it to work. But I would still like to figure out why populate is not working for me, as the official docs have a clear example of it working and the research I've done doesn't seem to indicate that the official docs are wrong. — Quincy

Christian Christian · Accepted Answer · 2020-10-22T11:26:02

Your first both sources are using an array of refs. As stated in your first source:

'sort' apply to the Author model, not the Book model.

In your example you would need an array of semesters in your semesterReferenceSchema. Than you can sort the array by year.

Mongoose populate sort option

1 Answers