This is how to model a one-to-one relationship with Mongo and Mongoose.

Establish Connection

mongoose.connect(MONGO_URL, () => 'Database connected!');

Example Models

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const UserSchema = new Schema({
  name: {
    type: String
  },
  account: {
    type: Schema.Types.ObjectId,
    ref: 'Account'
  }
});

const AccountSchema = new Schema({
  account_number: {
    type: String
  }
});

const User = mongoose.model('User', UserSchema);
const Account = mongoose.model('Account', AccountSchema);

Query a User with Associated Account

User.find({})
  .populate('account')
  .exec((error, accounts) => {
    // Now the 'account' field will be populated with the data in the accounts table.
  });