具有多个 SharePoint CAML 查询的 jQuery 延迟/承诺

Question

大家好，我有来自三个独立 SharePoint 列表的三个异步调用，每个查询都有一个返回对象和数组的成功回调。我希望在所有三个成功回调返回后执行另一个函数。我不知道如何让它与 jQuery deferreds 一起工作。我的代码如下。请帮助我了解如何使用延迟来实现上述目标。

function managementMain() {
    //From here I want to call the third function after executing 
      the managementQuery function.
      outPutObj = managementQuery();
    //Execute some third function with outPutObj:
    third function(outPutObj);
}
function managementQuery() {
    //CAML definition 1 here.
    clContext.executeQueryAsync(Function.createDelegate(this, function () { var soObj = onSOQuerySucceeded(); }), Function.createDelegate(this, this.onQueryFailed));
    //CAML definition 2 here.
    clContext.executeQueryAsync(Function.createDelegate(this, function () { var poObj = onPOQuerySucceeded(); }), Function.createDelegate(this, this.onQueryFailed));
   //CAML definition 3 here.
   clContext.executeQueryAsync(Function.createDelegate(this, function () { var salesRepNamesList = onSalesRepNamesQuerySucceeded(); }), Function.createDelegate(this, this.onQueryFailed));
   return {
       soObj: soObj,
       poObj: poObj,
       salesRepList: salesRepNamesList
   }
}
function onSOQuerySucceeded() {
     //Do something with the SharePoint List and return an object called soObj.
}
function onSalesRepNamesQuerySucceeded() {
     //Do something with the SharePoint List and return an array called salesRepNames.
}
function onPOQuerySucceeded() {
     //Do something with the SharePoint List and return an object called poObj.
}

我遇到的问题是 soObj、poObj 和 salesRepNamesList 可能不会按时返回 managementQuery 函数返回。因此，outPutObj 可能在执行第三个函数时定义不正确。请指教。谢谢。

Answer 1

首先，代码比它需要的要复杂：

• 您可以清除Function.createDelegate()，它 (a) 不是标准的 javascript，(b) 没有必要，因为应用它的函数都没有使用 this。 Microsoft 有点顽皮，在他们的示例中包括 Function.createDelegate()，因为它似乎与使用 clientContext.executeQueryAsync() 密切相关，但事实并非如此。
• 按照惯例，带有Async 后缀的方法应该返回一个promise，从而无需创建/解析您自己的Deferred。但是，Microsoft 再次有点调皮，clientContext.executeQueryAsync() 不 遵循惯例。

其次，如果不先聚合提供数据的 Promise，就无法聚合异步派生的数据。如给定的那样，问题中的代码缺少任何承诺聚合。由于这是 jQuery，我们希望在代码中的某处看到 jQuery.when()。

---

关于承诺，最简洁的方法总是在最低级别进行承诺——在这种情况下，为clientContext.executeQueryAsync() 编写一个可重用的适配器函数，它返回所需的承诺。这将大大简化更高级别的函数managementQuery()。

这是承诺：

clContext.executeQueryAsync_ = function() {
    return $.Deferred(function(dfrd) {
        clContext.executeQueryAsync(function(sender,args) {
            dfrd.resolve({'sender':sender, 'args':args});
        }, function(sender,args) {
            dfrd.reject({'sender':sender, 'args':args})
        });
    }).promise();
};

现在，managementQuery() 可以写成没有 Deferreds 和没有 Function.createDelegate()，如下所示：

function managementQuery() {
    var query = clContext.executeQueryAsync_;  // If clContext.executeQueryAsync() returns a promise, then assign clContext.executeQueryAsync() instead.
    var promise1 = query(/* so params */);
    var promise2 = query(/* po params */);
    var promise3 = query(/* salesRep params */);

    // Now aggregate the three promises with $.when(), and chain .then() to handle the delivered data.
    return $.when(promise1, promise2, promise3)
    .then(function(soObj, poObj, salesRepObj) {
        // soObj, poObj and salesRepObj each have .sender and .args properties.
        // Now the required object can be created and returned 
        // to become the data delivered (in a promise) by managementQuery().
        return {
            'soObj': onSOQuerySucceeded(),
            'poObj': onPOQuerySucceeded(),
            'salesRepList': onSalesRepNamesQuerySucceeded()
        };
    });
}

而managementMain()可以写成如下：

function managementMain() {
    return managementQuery()
    .then(someOtherFunction) // someOtherFunction will be automagically passed the object created/returned above.
    .fail(function(e) {
        // Any promise rejection in managementQuery() or someOtherFunction will end up here.
        console.log(e);
        this.onQueryFailed();
    });
}

Answer 2

您实际上将创建 3 个延迟对象，每个异步请求一个。完成异步请求后，您将在延迟对象上调用 .resolve 方法

// query will return a promise
outputPromise = query();

// your third function needs to wait for the promise to resolve
// to ensure the wait, you use the .then() method on the promise above
outputPromise.then(function(outputObj) {
    thirdFunction(outputObj);
});

function query() {
    // Create deferred objects
    var deferred1 = $.Deferred();
    var deferred2 = $.Deferred();

    clContext.executeQueryAsync(Function.createDelegate(this, function () { 
        var soObj = onSOQuerySucceeded();
        deferred1.resolve(soObj);
    }), Function.createDelegate(this, function () {
        this.onQueryFailed();
        deferred1.reject();
    }));

    clContext.executeQueryAsync(Function.createDelegate(this, function () { 
        var poObj = onPOQuerySucceeded();
        deferred2.resolve(poObj);
    }), Function.createDelegate(this, function() {
        this.onQueryFailed();
        deferred2.reject();
    }));

    // we must wait for all async ops to finish. to do this, we use the $.when() method
    // the $.when() method returns a promise that is resolved with the return
    // values of each deferred that was passed in. the then takes a callback
    // function and will spread each resolved value over the callback function's arguments
    return $.when(deferred1, deferred2).then(function(soObj, poObj) {
       // create the output object in the format you specified
       return {
           soObj: soObj,
           poObj: poObj
       }
    });
}

jQ Deferred 文档在这里：https://api.jquery.com/category/deferred-object/，以防您需要查找一些东西

作为旁注，我强烈建议使用另一个 Promise 库，例如 bluebird 或 Q，而不是 jQuery 的 deferreds。它们符合广泛接受的 Promise/A+ 规范和随后的 ES2015 Promise 规范。 jQ 3 将有一个符合 Promises/A+ 的 deferred，但 deferred 模式不在 ES2015 中，您应该使用其他库提供的 Promise 模式。