message: Use get with `relationshipsByName`
diff: import DS from 'ember-data';
  import RelationshipTracker from "ember-data-relationship-tracker";
  import { inject as service } from '@ember/service';
  -import { computed, defineProperty } from '@ember/object';
  +import { computed, defineProperty, get } from '@ember/object';
  import { readOnly, or } from '@ember/object/computed';
  import { capitalize } from '@ember/string';
  export default DS.Model.extend(RelationshipTracker, {
  resourceMetadata: service(),
  + relationshipTrackerVersionKey: 'version',
  +
  init() {
  this._super();
  let relationMap = this.constructor.relationshipsByName;
  @@ -39,7 +41,10 @@ export default DS.Model.extend(RelationshipTracker, {
  },
  async saveRelated() {
  - let relationshipsByName = this.constructor.relationshipsByName;
  + let relationshipsByName = get(this.constructor, 'relationshipsByName');
  + //TODO: Go through owned relationships and save the ones which `hasDirtyFields`
  + // and then recurse down to save their `hasDirtyFields` owned relations
  + // Save children first.
  let relatedSaves = this.dirtyRelationships.map(field => {
  let { kind } = relationshipsByName.get(field);
  let relatedRecords = kind === 'hasMany' ? this[field] : [ this.field ];
  