Cascade delete has many relations Ember Data

application-adapter.js

import DS from 'ember-data';

export default DS.JSONAPIAdapter.extend({
  deleteRecord(store, type, snapshot) {
    let recordsForUnloading = [];

    snapshot.eachRelationship((name, descriptor) => {
      let { options, kind, key } = descriptor;

      if (options.onDelete === 'unload' && kind === 'hasMany') {
        let records = snapshot.record.hasMany(key).value();

        if (records) {
          recordsForUnloading = recordsForUnloading.concat(records.toArray());
        }
      }
    });

    return this._super(...arguments).then((response) => {
      recordsForUnloading.forEach((record) => {
        record.unloadRecord();
      });

      return response;
    });
  }
});

comment-model.js

import Model from 'ember-data/model';
import { belongsTo } from 'ember-data/relationships';

export default Model.extend({
  post: belongsTo('post')
});

post-model.js

import Model from 'ember-data/model';
import { hasMany } from 'ember-data/relationships';

export default Model.extend({
  comments: hasMany('comment', { onDelete: 'unload' })
});