0_adapter.js

import ApplicationAdapter from './application';
import UrlTemplates from "ember-data-url-templates";

export default ApplicationAdapter.extend(UrlTemplates, {
  updateRecordUrlTemplate: '{+host}/posts/{id}{/updateEndpoint}',

  urlSegments: {
    updateEndpoint(type, id, snapshot) {
      return snapshot.get('_updateEndpoint');
    }
  },

  // Overriden method from RESTAdapter@v1.13.13
  // Do not forget to update with every ED upgrade
  updateRecord: function(store, type, snapshot) {
    var data = {};
    var serializer = store.serializerFor(type.modelName);

    serializer.serializeIntoHash(data, type, snapshot);

    var id = snapshot.id;
    var url = this.buildURL(type.modelName, id, snapshot, 'updateRecord');
    var verb = snapshot.get('_updateVerb') || "PUT";

    return this.ajax(url, verb, { data: data });
  },
});

1_model.js

import Ember from "ember";
import DS from "ember-data";

export default DS.Model.extend({
  // Your ED relationships and properties here...
  // ...

  // Custom API
  upvote() {
    this.setProperties({
      _updateEndpoint: 'upvote',
      _updateVerb:     'POST'
    });

    let promise = this.save();
    promise.finally(() => {
      this.setProperties({
        _updateEndpoint: null,
        _updateVerb: null
      });
    });

    return promise;
  },
  
  downvote() {
    this.setProperties({
      _updateEndpoint: 'downvote',
      _updateVerb:     'POST'
    });

    let promise = this.save();
    promise.finally(() => {
      this.setProperties({
        _updateEndpoint: null,
        _updateVerb: null
      });
    });

    return promise;
  },
});