异步处理提供数据并在必要时通过 http 检索数据的服务

Question

我有一个 angularJS 应用程序，它利用两个服务从数据库中检索数据。

session.js

angular.module('RiskAssessment').service('session', ['dbInterface', function(dbInterface) {
this.getBatches = function () {
    if (!this.batches) {
        console.log("Retrieved Batches");
        var that = this;
        return this.pullBatches().then(function (data) {
            that.batches = data; //Is this EVEN possible?
        });
    } else {
        console.log("Didn't retrieve Batches");
    }
    return this.batches;
};
this.pullBatches = function () {
    return dbInterface.pullBatches(this.getUserId());
};}]);

dbInterface.js

        pullBatches: function(userId){
            return $http.post('db_queries/get_batches.php', userId)
                .then(function (response) {
                    console.log("get_batches.php POST Result: ", response.data);
                    return response.data;
                })
                .catch(function (response) {
                    console.log("Error post");
                });
        }

我希望能够通过getBatches() 获得this.batches，如果它已经被检索和设置。否则，我想使用pullBatches() 来检索和设置this.batches。答案可能是各种承诺，但我正在为此苦苦挣扎。

感谢您的阅读！

编辑 ::

如何在.then() 调用.pullBatches() 的this.batches 中设置this.batches？

this.getBatches = function(){
    if(!this.batches) {
        console.log("Retrieved Batches");
        var deferred = $q.defer();
        deferred = this.pullBatches().then(function(data){
            //this.batches = data;  <---------------------------- HERE
        });
        return deferred.promise;
    }else{
        console.log("Didn't retrieve Batches");
    }
    return this.batches;
};

编辑 2 :: 在@Jahirul_Islam_Bhuiyan 的大力帮助下，我解决了我的问题。

this.getBatches = function(){
    var deferred = $q.defer();
    if(!this.batches){
        console.log("Retrieved Batches");
        dbInterface.pullBatches(this.getUserId()).then(function(payload){
            deferred.resolve(payload.data);
            service.setBatches(payload.data);
        });
    }else{
        console.log("Didn't retrieve Batches");
        deferred.resolve(this.batches);
    }
    return deferred.promise;
};

this.setBatches = function(batches){
    this.batches = batches;
};

在控制器中...

        session.getBatches().then(function(data){
            //console.log("getBatches.then() : " + JSON.stringify(data));
            $scope.batches = data;
        });

我现在对promises有了更深入的了解！

Answer 1

尝试关注

this.getBatches = function(){
   var deferred = $q.defer();
    if(!this.batches) {
        console.log("Retrieved Batches");

        this.pullBatches().then(function(data){
           deferred.resolve(data);
        });
    }else{
        console.log("Didn't retrieve Batches");
        deferred.resolve(this.batches);
    }
   var promises = [
            deferred.promise
        ];
    var promise = $q.all(promises);
        return promise;
};

希望有帮助