alias-404-double-load

controllers.application\.js

import Controller from '@ember/controller';
import { computed } from '@ember/object';
import { alias } from '@ember/object/computed';

export default Controller.extend({
  appName: 'Ember Twiddle',

	filterOne: computed('model.[]', 'model.@each.parent', function() {
  	return this.model.compact().filter(m => {
      m.get('parent');
      return true;
    });
  }),
  
  filterTwo: computed('filterOne.[]', function() {
  	return this.filterOne.filter(() => true);
  }),

	aliasOne: alias('filterTwo'),
	broken: computed('aliasOne.[]', function() {
    return this.aliasOne;
  }),
});

models.thing\.js

import Model from 'ember-data/model';

import attr from 'ember-data/attr';
import { belongsTo, hasMany } from 'ember-data/relationships';


export default Model.extend({
  name: attr('string'),
  parent: belongsTo('thing'),
})

routes.application\.js

import Route from '@ember/routing/route';
import Pretender from 'pretender';

const things = {
	data: [{
    type: 'thing',
    id: 1,
    attributes: {
      name: 'Child'
    },
    relationships: {
  		parent: {
      	data: {
        	type: 'thing',
          id: 404
        }
      }
  	}
  }]
};

export default Route.extend({
  beforeModel() {
    this.server = new Pretender(function() {
      this.get('/things', () => [200, {}, JSON.stringify(things)]);
      this.get('/things/:id', (req) => {
        console.info(`Requesting a single job: ${req.params.id}`);
        return [404, {}, 'Not found'];
      });
    });
    
    this.server.handledRequest = function(method, url, request) {
      console.groupCollapsed(`${method}: ${url}`);
      console.log(JSON.stringify(JSON.parse(request.responseText), null, 2));
      console.groupEnd();
    }
  },
  
  model() {
		return this.store.findAll('thing', { reload: true });
	}
});

templates.application\.hbs

<h1>404 race condition thing because of alias, I guess</h1>

<p>Some peculiar interaction I have narrowed down to <code>alias</code> is causing the <code>belongsTo</code> for the single model to be fetched twice.</p> 

<p>The first fetch errors with a 404 which is to be expected, but the second request throws a "Cannot read property 'isDestroying' of null" error due to the internalModel for the 404'd parent model no longer having a record.</p>

<p>I suspect this is due to a race condition in which the second request occurs before the internal model has settled from the first request. The currentState of the internal model suggests this too.</p>

<strong>Delete the broken line below to see that it is what causes the double 404.</strong>

<ol>
  <li>Model: {{model.length}}</li>
  <li>Filter One: {{filterOne.length}}</li>
  <li>Filter Two: {{filterTwo.length}}</li>
  <li>Alias One: {{aliasOne.length}}</li>
  <li>Broken: {{broken.length}}</li>
</ol>

twiddle\.json

{
  "version": "0.17.0",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.12.2",
    "ember-template-compiler": "3.12.2",
    "ember-testing": "3.12.2",
    "route-recognizer": "https://rawgit.com/tildeio/route-recognizer/56f5fcec6ae58d8e86b5dc77609809fb91198142/dist/route-recognizer.js",
    "FakeXMLHttpRequest": "https://rawgit.com/pretenderjs/FakeXMLHttpRequest/23c3a96b5b24f1bfe595867437e4f128a29c2840/fake_xml_http_request.js",
    "pretender": "https://rawgit.com/pretenderjs/pretender/c6de9afe18b1472aded2592f5a80ad9a26a0e262/pretender.js"
  },
  "addons": {
    "@glimmer/component": "1.0.0",
    "ember-data": "3.16.2"
  }
}