在循环中使用嵌套的 Promise 控制流程

Question

我在使用 Promise 控制我的方法流程时遇到了麻烦：

//FIND CHECKED OUT FILES
getCheckedOutFiles = function () {
    console.log('Get checked out files');
    var d = $q.defer();

    // Store final results and pass to then callback
    var checkedOutFiles = window.x = [];

    // Promise, returns collection with all sites 
    SiteService.getAllSites()
        .then(sites => {
            // For each site get lists then get items matching filter
            sites.forEach(function (site) {
                var web = new $pnp.Web(site.url);

                return web.lists
                    .filter("BaseTemplate eq 101")
                    .get() // Returns promise with all lists matching filter 
                    .then(lists => {
                        // Go through each list and find matching item 
                        lists.forEach(function (list) {
                            web.lists.getByTitle(list.Title).items
                                .filter("CheckoutUser ne null")
                                .expand("File, File/Author, File/ModifiedBy, File/CheckedOutByUser")
                                .get() // Returns promise with all items matching filter 
                                .then(files => {
                                    // Loop through each item, get properties, add to collection 
                                    files.forEach(function (f) {
                                        var fileObject = {
                                            fileName: f.File.Name,
                                            fileUrl: f.File.ServerRelativeUrl,
                                            absoluteUrl: f.File.ServerRelativeUrl,
                                            checkedTo: f.File.CheckedOutByUser.Title,
                                            modified: f.Modified,
                                            modifiedBy: f.File.ModifiedBy.Title,
                                            createdBy: f.File.Author.Title,
                                            created: f.Created,
                                            version: f.File.UIVersionLabel
                                        };
                                        // Add file to collection 
                                        checkedOutFiles.push(fileObject);
                                    }, this);
                                })
                                .catch(e => {
                                    console.log(e);
                                });
                        });
                        // "Ideally" - When all files retrieved return collection of results 
                        d.resolve(checkedOutFiles);
                        return null;
                    })
                    .catch(e => {
                        console.log(e);
                    });
            }, this);
            return null;
        });
    return d.promise;
};

// Returns promise with all checkedout file 
getCheckedOutFiles().then(files => {
    console.log("RESULTS", files);
    d.resolve(files);
});

我注意到console.log("RESULTS", files); 将在调用完成之前打印出来。调用完成后，window.x 将包含预期的数据。

Answer 1

使用Promise.all() 等待所有创建的promise，然后解析父promise

像这样（未测试）

//FIND CHECKED OUT FILES
getCheckedOutFiles = function () {
    console.log('Get checked out files');
    var d = $q.defer();

    // Store final results and pass to then callback
    var checkedOutFiles = window.x = [];

    // Promise, returns collection with all sites 
    SiteService.getAllSites()
        .then(sites => {
            // For each site get lists then get items matching filter
            sites.forEach(function (site) {
                var web = new $pnp.Web(site.url);

                return web.lists
                    .filter("BaseTemplate eq 101")
                    .get() // Returns promise with all lists matching filter 
                    .then(lists => {
                        let promises = []
                        // Go through each list and find matching item 
                        lists.forEach(function (list) {

                            let prom = web.lists.getByTitle(list.Title).items
                                .filter("CheckoutUser ne null")
                                .expand("File, File/Author, File/ModifiedBy, File/CheckedOutByUser")
                                .get() // Returns promise with all items matching filter 
                                .then(files => {
                                    // Loop through each item, get properties, add to collection 
                                    files.forEach(function (f) {
                                        var fileObject = {
                                            fileName: f.File.Name,
                                            fileUrl: f.File.ServerRelativeUrl,
                                            absoluteUrl: f.File.ServerRelativeUrl,
                                            checkedTo: f.File.CheckedOutByUser.Title,
                                            modified: f.Modified,
                                            modifiedBy: f.File.ModifiedBy.Title,
                                            createdBy: f.File.Author.Title,
                                            created: f.Created,
                                            version: f.File.UIVersionLabel
                                        };
                                        // Add file to collection 
                                        checkedOutFiles.push(fileObject);
                                    }, this);
                                })
                                .catch(e => {
                                    console.log(e);
                                });
                            promises.push(prom)
                        });
                        // "Ideally" - When all files retrieved return collection of results 
                        Promise.all(promises).then(function(){
                            d.resolve(checkedOutFiles);
                        })
                        return null;
                    })
                    .catch(e => {
                        console.log(e);
                    });
            }, this);
            return null;
        });
    return d.promise;
};

// Returns promise with all checkedout file 
getCheckedOutFiles().then(files => {
    console.log("RESULTS", files);
    d.resolve(files);
});

Answer 2

这些是需要解决的问题：

1. 您有两个单独的循环，您需要在其中管理 Promise。您需要将这些承诺收集到一个数组中，然后在它们上使用Promise.all() 以了解循环中的所有承诺何时完成。

2. 您通过创建 d 承诺然后手动解决它来使用反模式。相反，您应该返回 SiteService.getAllSites().then() 承诺，然后在其中返回承诺以链接，以便链接所有内容（包括正确的错误处理）。

3. 您的 .catch() 处理程序只是记录是“吃”错误。如果你 .catch() 并且不重新抛出，它会将这个承诺变成一个已解决的承诺，从而“吃掉”错误而不是传播它。

以下是解决这些问题的方法：

//FIND CHECKED OUT FILES
function getCheckedOutFiles() {
    console.log('Get checked out files');

    // Store final results and pass to then callback
    var checkedOutFiles = window.x = [];

    // Promise, returns collection with all sites 
    return SiteService.getAllSites().then(sites => {
            // For each site get lists then get items matching filter
            var promises = [];
            sites.forEach(function (site) {
                var web = new $pnp.Web(site.url);

                promises.push(web.lists
                    .filter("BaseTemplate eq 101")
                    .get() // Returns promise with all lists matching filter 
                    .then(lists => {
                        // Go through each list and find matching item 
                        var promises2 = [];
                        lists.forEach(function (list) {
                            promises2.push(web.lists.getByTitle(list.Title).items
                                .filter("CheckoutUser ne null")
                                .expand("File, File/Author, File/ModifiedBy, File/CheckedOutByUser")
                                .get() // Returns promise with all items matching filter 
                                .then(files => {
                                    // Loop through each item, get properties, add to collection 
                                    files.forEach(function (f) {
                                        var fileObject = {
                                            fileName: f.File.Name,
                                            fileUrl: f.File.ServerRelativeUrl,
                                            absoluteUrl: f.File.ServerRelativeUrl,
                                            checkedTo: f.File.CheckedOutByUser.Title,
                                            modified: f.Modified,
                                            modifiedBy: f.File.ModifiedBy.Title,
                                            createdBy: f.File.Author.Title,
                                            created: f.Created,
                                            version: f.File.UIVersionLabel
                                        };
                                        // Add file to collection 
                                        checkedOutFiles.push(fileObject);
                                    }, this);
                                })
                                .catch(e => {
                                    console.log(e);
                                    // propagate error
                                    throw e;
                                }));
                        });
                        return Promise.all(promises2);
                    }).catch(e => {
                        console.log(e);
                        // propagate error
                        throw e;
                    }));
            }, this);
            return Promise.all(promises).then(() => {
                // make checkedOutFiles by the final resolve value
                return checkedOutFiles;
            });
        });
};

// Returns promise with all checkedout file 
getCheckedOutFiles().then(files => {
    console.log("RESULTS", files);
}).catch(err => {
    // handle error here
});

这可以通过在 Bluebird Promise 库中使用 Promise.map() 来简化，它将迭代一个数组，调用一个 Promise 生成函数并等待所有 Promise 完成（.each() 和 Promise.all() 的组合） .