app/models/activity-group.js
import Base from 'client/models/-base';
import attr from 'ember-data/attr';
import { hasMany } from 'ember-data/relationships';
export default Base.extend({
group: attr('string'),
isRead: attr('boolean', { defaultValue: true }),
isSeen: attr('boolean', { defaultValue: true }),
activities: hasMany('activity', { inverse: null })
});