form-input-subclass.js

import FormInput from './form-input';

var displayValuePath = 'name';

export default FormInput.extend({

  valid: function() {
    // Values in 'selection' are always promise proxies for models. By this
    // point, they should *always* be resolved, so _data should have a model in
    // it (or null).
    var selection = this.get('selection');

    if (selection && selection._data) {
      return true;
    }

    return false;
  }.property('selection'),

  selection: function() {
    var value = this.get('value');
    return this.get('content').findBy(displayValuePath, value);
  }.property('value', 'content'),

  meaninglessProperty: function() {
    return true;
  }.property('value')

});

form-input.js

import Ember from 'ember';

export default Ember.TextField.extend({
  classNameBindings: ['error'],

  /**
   * Whether the field is currently in an error state.
   */
  error: function() {

    if (this.get('required')) {
      return !this.get('valid');
    }

    return true;
  }.property('valid'),

  required: true,

  /**
   * Whether the current value of the field is valid. By default, any truthy
   * value is valid. Doesn't take 'required' into account.
   */
  valid: function() {
    if (this.get('value')) {
      return true;
    }

    return false;
  }.property('value')

});