Mongoose : query on a field on an array of ref documents,

Question

here are my models:

var LocationSchema = new Schema(
{
    events: [
        {
            type: mongoose.Schema.Types.ObjectId,
            ref: 'Event'
        }
    ]
})
var EventSchema = new Schema(
{
    title  : String,

    location: {
        type: mongoose.Schema.Types.ObjectId,
        ref: 'Location'
    }
})

I would like to query from the Location model a field inside the Event model.

The following one doesn't work

findOne({events: {$elemMatch: {title: 'test'}}})

I'm not sure even that's possible to make it ...

It's not possible, which is why you use emedding instead.There is a section somewhere in the docs that shows using `.filter()`, — Blakes Seven, Jul 15 '15 at 09:23
Thank you guys, I did with the populate, but it's not too greedy to request ALL the documents, and to filter after ? — GuillaumeC, Jul 15 '15 at 10:04
Why do you want to query from Location when you're looking for something inside the Event model/collection? — robertklep, Jul 15 '15 at 11:04
@robertklep because I have fields in my Location model that I want to select too — GuillaumeC, Jul 15 '15 at 13:22

score 6 · Accepted Answer · answered Jul 15 '15 at 13:30

When you use references you can use population to run a "sub query" on referenced documents to select which ones should be included.

Location.find({ ... }).populate({
  path  : 'events',
  match : { title : 'test' }
}).exec(...);

Which way around (query Location and populate Event, or the other way around) depends on the exact query you need to run. It's most performant to run the "main" query on the model that will yield the least results.

This method will still return all documents that matched the main query, and you have to perform some postprocessing to filter the documents that don't have any matched event references.

How would you query the other way arround (if you have few selection criterion on Location) without writing two queries ? — user1767316, Oct 29 '18 at 09:47

Mongoose : query on a field on an array of ref documents,

1 Answers1