Custom Class

Creating custom validators is very simple. To generate a validator named unique-username in Ember CLI

ember generate validator unique-username

This will create the following files

• app/validators/unique-username.js
• tests/unit/validators/unique-username-test.js

// app/validators/unique-username.js

import BaseValidator from 'ember-cp-validations/validators/base';

const UniqueUsername = BaseValidator.extend({
  validate(value, options, model, attribute) {
    return true;
  }
});

UniqueUsername.reopenClass({
  getDependentsFor(attribute, options) {
    return [];
  }
});

export default UniqueUsername;

Side Note: Before we continue, I would suggest checking out the documentation for the Base Validator.

If you want to interact with the store within your validator, you can simply inject the service like you would a component. Since you have access to your model and the current value, you should be able to send the server the right information to determine if this username is unique.

// app/validators/unique-username.js

import Ember from 'ember';
import BaseValidator from 'ember-cp-validations/validators/base';

const UniqueUsername = BaseValidator.extend({
  store: Ember.inject.service(),

  validate(value, options, model, attribute) {
    return this.get('store').findRecord('user', value).then((user) => {
      if(user && user.id === value) {
        let message = The username '${value}' already exists.;
        let meta = user.get('meta');

        if(get(options, 'showSuggestions') && meta && meta.suggestions) {
          message += "What about one of the these: " + meta.suggestions.join(', ');
        }
        return message;
      } else {
        return true;
      }
    })
  }
});

Dependent Keys

There will be times when your validator will be dependent on some other property or object. Instead of having to include them in your option's dependentKeys, you can declare them in the static getDependentsFor hook. This hook receives two parameters. The first is the attribute that this validator is being added to, and the second are the options there were passed to this validator.

From the above code sample:

// app/validators/unique-username.js

import BaseValidator from 'ember-cp-validations/validators/base';

const UniqueUsername = BaseValidator.extend({});

UniqueUsername.reopenClass({
  getDependentsFor(attribute, options) {
    return [];
  }
});

export default UniqueUsername;

All dependent keys are in reference to the model's validations.attrs object. So when you return ['username'], it will add a dependent to model.validations.attrs.username. If you want to add a dependent on the model, your key needs to be prefixed with model. So when you return ['model.username'], it will add a dependent to model.username instead of model.validations.attrs.username. This means that if you have a dependent on a service, that service must be injected into the model since returning ['model.myService.someProperty'] will be interpreted as model.myService.someProperty.

Usage

To use our unique-username validator we just have to add it to the model definition

var Validations = buildValidations({
  username: validator('unique-username', {
    showSuggestions: true
  }),
});

export default DS.Model.extend(Validations, {
  'username': DS.attr('string'),
});

Testing

As mentioned before, the generator created a unit test for your new custom validator.

// tests/unit/validators/unique-username-test.js

import Ember from 'ember';
import { moduleFor, test } from 'ember-qunit';

moduleFor('validator:unique-username', 'Unit | Validator | unique-username', {
    needs: ['validator:messages']
});

test('it works', function(assert) {
    var validator =  this.subject();
    assert.ok(validator);
});

A simple test for our validation method can be as such

test('username is unique', function(assert) {
    assert.expect(1);

    let validator =  this.subject();
    let done = assert.async();

    validator.validate('johndoe42').then((message) => {
      assert.equal(message, true);
      done();
    });
});