Populate a mongoose model with a field that isn't an id - node.js

Question

Is it possible to populate a mongoose model with a field of a reference model that isn't the _id ... e.g. a username.
so something like
var personSchema = Schema({
_id : Number,
name : String,
age : Number,
stories : { type: String, field: "username", ref: 'Story' }
});

Answer 1

This is supported since Mongoose 4.5, and is called virtuals population.
You have to define your foreign keys relationships after your schemas definitions and before creating models, like this:
// Schema definitions
BookSchema = new mongoose.Schema({
...,
title: String,
authorId: Number,
...
},
// schema options: Don't forget this option
// if you declare foreign keys for this schema afterwards.
{
toObject: {virtuals:true},
// use if your results might be retrieved as JSON
// see http://stackoverflow.com/q/13133911/488666
//toJSON: {virtuals:true}
});
PersonSchema = new mongoose.Schema({id: Number, ...});
// Foreign keys definitions
BookSchema.virtual('author', {
ref: 'Person',
localField: 'authorId',
foreignField: 'id',
justOne: true // for many-to-1 relationships
});
// Models creation
var Book = mongoose.model('Book', BookSchema);
var Person = mongoose.model('Person', PersonSchema);
// Querying
Book.find({...})
// if you use select() be sure to include the foreign key field !
.select({.... authorId ....})
// use the 'virtual population' name
.populate('author')
.exec(function(err, books) {...})

Answer 2

It seems they enforce to use _id, and maybe we can customize it in the future.
Here is the issue on Github https://github.com/LearnBoost/mongoose/issues/2562

Answer 3

This is an example of using the $lookup aggregate to populate a model called Invite with the respective User based on the corresponding email field:
Invite.aggregate(
{ $match: {interview: req.params.interview}},
{ $lookup: {from: 'users', localField: 'email', foreignField: 'email', as: 'user'} }
).exec( function (err, invites) {
if (err) {
next(err);
}
res.json(invites);
}
);
It's probably quite similar to what you're trying to do.

Answer 4

To add to Frosty's answer, if you're looking to refer to an array of documents of another collection you would make changes like so.
BookSchema = new mongoose.Schema(
{
title: String,
authorId: [Number],
},
// schema options: Don't forget this option
// if you declare foreign keys for this schema afterwards.
{
toObject: { virtuals: true },
// use if your results might be retrieved as JSON
// see http://stackoverflow.com/q/13133911/488666
toJSON: {virtuals:true}
});
PersonSchema = new mongoose.Schema({ id: Number, name: String });
BookSchema.virtual("author", {
ref: "Person",
localField: ["authorId"],
foreignField: ["id"],
// justOne: true, // Needs to be commented out in this scenario,
});

Answer 5

You may use the populate() API.
The API is more flexible, you don't have to specify ref and field in the Schema.
http://mongoosejs.com/docs/api.html#document_Document-populate
http://mongoosejs.com/docs/api.html#model_Model.populate
You can mix and match with find().