Mongoose, sort query by populated field

Question

Mongoose, sort query by populated field

As far as I know, it's possible to sort populated docs with Mongoose (source).

I'm searching for a way to sort a query by one or more populated fields.

Consider this two Mongoose schemas :

var Wizard = new Schema({
    name  : { type: String }
, spells  : { [{ type: Schema.ObjectId, ref: 'Spell' }] }
});

var Spell = new Schema({
    name    : { type: String }
,   damages : { type: Number }
});

Sample JSON:

[{
    name: 'Gandalf',
    spells: [{
            name: 'Fireball',
            damages: 20
        }]
}, {
    name: 'Saruman',
    spells: [{
            name: 'Frozenball',
            damages: 10
        }]
}, {
    name: 'Radagast',
    spells: [{
            name: 'Lightball',
            damages: 15
        }]
}]

I would like to sort those wizards by their spell damages, using something like :

WizardModel
  .find({})
  .populate('spells', myfields, myconditions, { sort: [['damages', 'asc']] })
// Should return in the right order: Saruman, Radagast, Gandalf

I'm actually doing those sorts by hands after querying and would like to optimize that.

javascript
node.js
mongodb
sorting
mongoose

Answer 1

Ask yourself(and here are the answers):

What I want? Sort wizards by their spell damage(it should be an aditional field, probably the sum of the spells damage.

What I did: I have sorted the SPELLS of the wizard.

What should you do: Wizard.find({}).sort({ power : 'asc' }) and then populate with spells and do whatever you like. Power is another field in Wizard. You will need it because even if you populate your spells, you will have an array of spells and it won't help you.

Hope this helps.

Answer 2

You can implicitly specify only required parameters of populate method:

WizardModel
  .find({})
  .populate({path: 'spells', options: { sort: [['damages', 'asc']] }})

Have a look at http://mongoosejs.com/docs/api.html#document_Document-populate Here is an example from a link above.

doc
.populate('company')
.populate({
  path: 'notes',
  match: /airline/,
  select: 'text',
  model: 'modelName'
  options: opts
}, function (err, user) {
  assert(doc._id == user._id) // the document itself is passed
})

Answer 3

The above syntax looks correct, it should work v2.4.1 onwards.
https://groups.google.com/forum/#!msg/mongoose-orm/6t-AzCSPgHs/mo4fpWYSes8J