An attempt to find the best way to structure a Restangularized API service

poemsApiService.js

(function() {
'use strict';

/**
 * the poemsApi Service. Restangular has all the functions you would expect from an
 * API service, so we return the Restangular resource object.
 * 
 * @service poemsApi
 * @param Restangular bower install restangular
 * @return service object
 */
var poemsApi = function poemsApi(Restangular) {

    var service = Restangular.all('poems');
    return service;
};

/**
 * We use the RestangularProvider to add custom methods and custom paths.
 * Other modules can use addElementTransformer themselves on your API
 * to add custom fields to the resource
 */
poemsApi.setConfig = function setPoemsApiConfig(RestangularProvider) {
    
    // every Restangular.all('poems') or Restangular.one('poems', someId) will make this function
    // run on every element
    RestangularProvider.addElementTransformer('poems', false, function transformPoemElements(poem) {
        
        // custom functions for complex url paths
        // addRestangularMethod(name, operation, [path, params, headers, elem])
        poem.addRestangularMethod('flag', 'post', 'flag/myWeirdUrl', { source: 'myWebapp'}, { 'Accept': 'myweird/mimetype'});
        // now calling poem.flag() will POST to flag/myWeirdUrl, with these parameters and with this particular header
        
        // custom properties (for UX purposes), allows server-side to take it over
        poem.isSelected = poem.isSelected || false;
        
        // custom method
        (poem.setValidationFromSchema = function setValidationFromSchema(schema) {
            
            poem.all('schema').get().then(function getSchema(schema) {
                poem.schema = schema;

                poem.validate = function() {
                    // some validation code
                };
            });

        })();
        
        return poem;
    });
};

// give it to Angular
angular.module('app')
.factory('poemsApi', poemsApi)
.config(poemsApi.setConfig);

})();