int-array-serializer.js

import Ember from 'ember';

export default Ember.Mixin.create({
    serializeQueryParam(value, urlKey, defaultValueType) {
        if (defaultValueType === 'array') {
            return value;
        } else {
            return this._super.call(this, ...arguments);
        }
    },

    deserializeQueryParam(value, urlKey, defaultValueType) {
        if (defaultValueType === 'array') {
            return value.map(item => {
                return parseInt(item, 10);
            });
        } else {
            return this._super.call(this, ...arguments);
        }
    }
});

route.js

import Ember from 'ember';
import IntArraySerializer from '../../../mixins/route/int-array-serializer';

export default Ember.Route.extend(IntArraySerializer, {
    (...)
});