[Angular-Scaled Web] 9. Control your promises with $q

Learn how to manually control how asynchronous requests are handled with the use of promises. Because $http is built to work with promises, we saw a foreshadow of them in the previous lesson. We will take this a step further but seeing how to manually create a promise and then resolve or reject it as we see fit.

angular.module('eggly.models.categories', [

])
    .service('CategoriesModel', function ($http, $q) {
        var CategoriesModel = {},
            URLS = {
                FETCH: 'data/categories.json'
            },
            categories;


        function extract(result) {
            return result.data;
        }

        function cacheCategories(result) {
            categories = extract(result);
            return categories;
        }

        CategoriesModel.getCategories = function() {
            return (categories) ? $q.when(categories) : $http.get(URLS.FETCH).then(cacheCategories);
        };

        CategoriesModel.getCategoryByName = function(categoryName) {

            function findCategory(){
                return _.find(categories, function(c){
                    return c.name == categoryName;
                })
            }

            return $q(function(resolve, reject) {
                //resolve it when categories are set
                if(categories){
                    resolve(findCategory());
                }else{
                    //if not set, get the categories
                    CategoriesModel.getCategories()
                        .then(function() {
                            resolve(findCategory());
                        })
                }
            })
        };

        return CategoriesModel;
    })
;