Preloading

adapters.application\.js

export default class Adapter {
  constructor(args) { Object.assign(this, args); }
  static create(args) { return new this(args); }
  
  findRecord(store, schema, id, snapshot) {
  	let type = schema.modelName;
    console.log({ type, id }, snapshot);
    
    if (type === 'post') {
      let authorId = snapshot.belongsTo('author', { id: true });
      console.log({ authorId });
      let doc = {
        data: {
          type,
          id,
          attributes: {
            title: 'first post'
          },
          relationships: {
            author: {
              data: { type: 'user', id: '123' }
            }
          }
        }
      };
      console.log({ doc });
      return doc;
    }
    throw new Error('tried to get author');
  }
}

controllers.application\.js

import Controller from '@ember/controller';

export default class ApplicationController extends Controller {
  appName = 'Ember Twiddle';
}

models.post\.js

import Model from 'ember-data/model';

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


export default class extends Model {
  @attr title;
  @belongsTo('user', { async: true, inverse: 'posts' }) author;
}

models.user\.js

import Model from 'ember-data/model';

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


export default class extends Model {
  @attr name;
  @hasMany('post', { async: true, inverse: 'author' }) posts;
}

routes.application\.js

import Route from '@ember/routing/route';
import { inject } from '@ember/service';

export default class MyRoute extends Route {
  @inject
  store;
  
  async model() {
    let record = await this.store.findRecord('post', '1', { include: 'author', preload: { author: 'abc' } });
    console.log(record);
    return record;
  }
}

serializers.application\.js

export default class Serializer {
  constructor(args) { Object.assign(this, args); }
  static create(args) { return new this(args); }
  normalizeResponse(_,__, p) { console.log(p); return p; }
}

templates.application\.hbs

<h1>Welcome to {{this.appName}}</h1>
<br>
<h1>{{@model.title}}</h1>
<br>
{{outlet}}
<br>
<br>

twiddle\.json

{
  "version": "0.17.1",
  "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/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0",
    "ember-data": "3.18.0"
  }
}