Package: mongoose-embed-populate

Package useful for populating references to sub documents. It will add a query builder helper and a model's method helper.

N.B: Using sub references is considered in most of the cases an anti-pattern that you should avoid (usually you can re-organize your data to avoid it).

Install

npm i mongoose-embed-populate

Setup

// Including the library will add 'subPopulate' helper for query
const subReferencesPopulate = require('mongoose-embed-populate');

const TestSchema = new mongoose.Schema({});

// Applying as plugin on the schema will provide 'subPopulate' method on the model
TestSchema.plugin(subReferencesPopulate);
const TestModel = mongoose.model('Test', TestSchema);

Usage

Defining a sub reference

To an Array of SubDocuments

For example:

const PersonSchema = new mongoose.Schema({
  name: {
    type: String,
  },
  contacts: [
    {
      email: {
        type: String,
      },
    },
  ],
});
const PersonModel = mongoose.model('Person', PersonSchema);

const MessageSchema = new mongoose.Schema({
  contact: {
    type: mongoose.Schema.Types.ObjectId,
    subRef: 'Person.contacts',
  },
  content: {
    type: String,
  },
});
MessageSchema.plugin(subReferencesPopulate);
const MessageModel = mongoose.model('Message', MessageSchema);

The subRef: 'Person.contacts' will do the magic. You can now call the following methods:

    const message = await MessageModel.findById(...);
    message.subPopulate('contact');

    // or
    const subPopulatedResults = await MessageModel.find(..).subPopulate('contact');

The field 'contact' will be populated with the corresponding referenced sub document.

To an Array of References

For example:

const ContactSchema = new mongoose.Schema({
  email: {
    type: String,
  },
});
const ContactModel = mongoose.model('Contact', ContactSchema);

const PersonSchema = new mongoose.Schema({
  name: {
    type: String,
  },
  contacts: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Contact' }],
});
const PersonModel = mongoose.model('Person', PersonSchema);

const MessageSchema = new mongoose.Schema({
  contact: {
    type: mongoose.Schema.Types.ObjectId,
    subRef: 'Person.contacts',
  },
  content: {
    type: String,
  },
});

MessageSchema.plugin(subReferencesPopulate);
const MessageModel = mongoose.model('Message', MessageSchema);

You might think it would be better to put a direct reference to the ContactModel instead of Person.contacts. The difference will be: if it doesn't exist a Person with the referenced sub document than contact will not be sub populated even if it has the right _id to an existing Contact. If you sub populate this way, you're sure that a Person has that contact.

Bound to fields

If you want to increase the performance of the queries, it is possibile to use the boundTo schemaType options:

const PersonSchema = new mongoose.Schema({
  name: {
    type: String,
  },
  contacts: [
    {
      email: {
        type: String,
      },
    },
  ],
});
const PersonModel = mongoose.model('Person', PersonSchema);

const MessageSchema = new mongoose.Schema({
  person: {
    type: mongoose.Schema.Types.ObjectId,
    ref: 'Person',
    required: true,
  },
  contact: {
    type: mongoose.Schema.Types.ObjectId,
    subRef: 'Person.contacts',
    boundTo: 'person',
  },
  content: {
    type: String,
  },
});
MessageSchema.plugin(subReferencesPopulate);
const MessageModel = mongoose.model('Message', MessageSchema);

Storing the root reference of where is the sub document we're interested in.

Nesting paths

Both subRef and boundTo allow any path you want. The most important thing is to remember it must ends with a schema type Array of References or Array of Sub Documents and it must have not arrays in the between path.

Object --- > Object ---> .... any time you want ---> Array

Test

You can try the tests using the following command ( before you need to change the connection to MongoDB ) :

npm install --test
npm run test

See also

If you want to provide an integrity to your sub references, you could be interested in sub-references-integrity

Support

If you would like to support my work, please buy me a coffe ☕. Thanks in advice.