One way association

AKA "Belongs To"

Overview

A one way association is where a model is associated with another model. You could query that model and populate to get the associated model. You can't however query the associated model and populate to get the associating model.

One Way Example

In this example, we are associating a User with a Pet but not a Pet with a User.

javascript

// myApp/api/models/Pet.js
module.exports = {
  attributes: {
    name: {
      type: 'string'
    },
    color: {
      type: 'string'
    }
  }
}

javascript

// myApp/api/models/User.js
module.exports = {
  attributes: {
    name: {
      type: 'string'
    },
    age: {
      type: 'number'
    },
    pony:{
      model: 'Pet'
    }
  }
}

Now that the association is setup, you can populate the pony association.

javascript

var usersWithPonies = await User.find({ name:'Mike' }).populate('pony');
  // The users object would look something like:
  // [{
  //  name: 'Mike',
  //  age: 21,
  //  pony: {
  //    name: 'Pinkie Pie',
  //    color: 'pink',
  //    id: 5,
  //    createdAt: Tue Feb 11 2014 15:45:33 GMT-0600 (CST),
  //    updatedAt: Tue Feb 11 2014 15:45:33 GMT-0600 (CST)
  //  },
  //  createdAt: Tue Feb 11 2014 15:48:53 GMT-0600 (CST),
  //  updatedAt: Tue Feb 11 2014 15:48:53 GMT-0600 (CST),
  //  id: 1
  // }]

Notes

Because we have only formed an association on one of the models, a Pet has no restrictions on the number of User models it can belong to. If we wanted to, we could change this and associate the Pet with exactly one User and the User with exactly one Pet.