extending.md

Extending Database Adapters

Now that we talked about pagination, sorting and querying we can look at different ways you can extend the functionality of the existing database adapters.

ProTip: Keep in mind that calling the original service methods will return a Promise that resolves with the value.

Hooks

The most flexible option is weaving in functionality through hooks. For a more detailed explanation about hook, go to the hooks chapter. For example, createdAt and updatedAt timestamps could be added like this:

const feathers = require('feathers');
const hooks = require('feathers-hooks');

// Import the database adapter of choice
const service = require('feathers-<adapter>');

const app = feathers()
  .configure(hooks())
  .use('/todos', service({
    paginate: {
      default: 2,
      max: 4
    }
  }));

app.service('todos').before({
  create(hook) {
    hook.data.createdAt = new Date();
  },
  
  update(hook) {
    hook.data.updatedAt = new Date();
  }
});

app.listen(3030);

Another important hook that you will probably use eventually is limiting the query for the current user (which is set in params.user by authentication):

app.service('todos').before({
  // You can create a single hook like this
  find: function(hook) {
    const query = hook.params.query;

    // Limit the entire query to the current user
    query.user_id = hook.params.user.id;
  }
});

Classes (ES6)

All modules also export an ES6 class as Service that can be directly extended like this:

'use strict';

const Service = require( 'feathers-<database>').Service;

class MyService extends Service {
  create(data, params) {
    data.created_at = new Date();

    return super.create(data, params);
  }

  update(id, data, params) {
    data.updated_at = new Date();

    return super.update(id, data, params);
  }
}

app.use('/todos', new MyService({
  paginate: {
    default: 2,
    max: 4
  }
}));

Uberproto (ES5)

You can also use .extend on a service instance (extension is provided by Uberproto):

const myService = memory({
  paginate: {
    default: 2,
    max: 4
  }
}).extend({
  create(data) {
    data.created_at = new Date();
    return this._super.apply(this, arguments);
  }
});

app.use('/todos', myService);

Note: this is more for backwards compatibility. We recommend the usage of classes or hooks as they are easier to test, easier to maintain and are more flexible.