serializers...application.js

/* app/serializers/application.js */
normalizeFindRecordResponse(store, primaryModelClass, payload) {
 const _p = payload.data;
 const relationships = _p.relationships;
 if (relationships) {
   Object.keys(_p.relationships).forEach((related_key) => {
     // m2m
     if (Array.isArray(relationships[related_key].data)) {
       _p.attributes[`${related_key}-ids`] =  relationships[related_key].data.mapBy(‘id’);
     // belongs_to
     } else if (relationships[related_key].data) {
       _p.attributes[`${related_key}-id`] = relationships[related_key].data.id;
     }
   });
 }
 return this._super(…arguments);
}