Populate a mongoose model with a field that isn't an id

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' }
});

Fast forward to 2017, and Frosty's answer should be the accepted answer. — Richard Morgan, Jan 31 '17 at 01:34

Maxime Pacary · Answer 1 · 2019-04-02T10:01:33.487

102

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) {...})

edited Apr 02 '19 at 10:01

answered Oct 05 '16 at 08:57

Maxime Pacary

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I just assume it as the answer – Jacob Jan 22 '19 at 00:00
It is returning all properties of `author`, how do I specify the `.populate('author')` to only return specific fields? – jet_choong Mar 19 '22 at 07:46
Ah, found the answer in the docs, https://mongoosejs.com/docs/populate.html#field-selection. Anyway thanks for the asnwer. – jet_choong Mar 19 '22 at 07:47
It this work in nestjs/mongoose also? – Nikunj Aggarwal Jan 12 '23 at 09:15
Yes, but the syntax is different. Everything is explained in this doc page https://docs.nestjs.com/techniques/mongodb (search for keyword "relation"). – Maxime Pacary Jan 13 '23 at 13:08

Leo Gao · Answer 2 · 2015-01-30T10:05:55.830

3

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

edited Jan 30 '15 at 10:05

answered Jan 29 '15 at 07:58

Leo Gao

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This github issue was closed in favor of using the new [virtuals population](https://mongoosejs.com/docs/populate.html) – steampowered Aug 19 '19 at 18:42

score 3 · Answer 3 · answered Mar 15 '16 at 20:54

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.

JLange · Answer 4 · 2022-05-19T07:43:15.533

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, 
});

score -7 · Accepted Answer · answered Oct 10 '13 at 07:58

-7

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().

answered Oct 10 '13 at 07:58

leesei

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I can't understand from the docs. Could you give an example query? – bogdan.herti May 14 '14 at 13:01
8

Coming to SO only after reading the documentation, if I understood it I wouldn't search for answers here. – Azder Jul 24 '14 at 05:58
You still need to configure your Schema for populate to be use, by adding reference. – lukaserat Sep 09 '16 at 09:34

Populate a mongoose model with a field that isn't an id

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