Promise內部Promise在Bluebird Node.js中創建難以管理的結構

Question

我的查詢如下所示：

checkUserId(user_email).then((info) => {
                    changeBookStatus(bookInfo._id, borrow).then(() => {
                        issueReturnBook(info._id, bookInfo._id,
                            due_date + "/" + due_month, borrow).then((savedInfo) => {
                            console.log("saved info " + savedInfo._id);
                            LibraryTransaction.findById(savedInfo._id).
                            populate('UserDetails').populate('BookDetails').exec((err, libInfo) => {
                                res.json({
                                    status: '200',
                                    message: 'transaction completed',
                                    data: libInfo
                                });
                            });

                        }).catch((err) => {
                            res.json({
                                status: '500',
                                message: err
                            });
                        });
                    }).catch((err) => {
                        res.json({
                            status: '500',
                            message: err
                        });
                    });
                })


const issueReturnBook = (user_id, book_id, due_date, borrow) => {
    let borrowReturn;
    if (borrow == '0') {
        borrowReturn = false;
    } else if (borrow == '1') {
        borrowReturn = true;
    }
    return new Promise((resolve, reject) => {
        const libraryTransaction = new LibraryTransaction();
        libraryTransaction.UserDetails = user_id;
        libraryTransaction.BookDetails = book_id;
        libraryTransaction.DueDate = due_date;
        libraryTransaction.BorrowReturn = borrowReturn;
        libraryTransaction.save().then((info) => {
            if (!info) {
                reject(false);
            }
            resolve(info);
        }).catch((err) => {
            reject(err);
        });
    });
};


const changeBookStatus = (book_id, borrow) => {
    let borrowStat;
    if (borrow == '0') {
        borrowStat = false;
    } else if (borrow == '1') {
        borrowStat = true;
    }
    return new Promise((resolve, reject) => {
        Books.findOneAndUpdate({ '_id': book_id }, { $set: { CurrentlyAvailableStatus: borrow } }).then((info) => {
            if (!info) {
                reject('there is no such book');
            }
            resolve(info);
        }).catch((err) => {
            reject(err);
        });
    });
};

const checkUserId = (user_email) => {
    return new Promise((resolve, reject) => {
        User.findOne({ 'Email': user_email.trim() }).then((info) => {
            if (!info) {
                reject('the is no such user');
            }
            resolve(info);
        }).catch((err) => {
            reject(err);
        });
    });
};

現在，那時內部太多了，還有沒有更好的方法可以有效地做到這一點？

Answer 1

很難確定哪些變量在范圍內，哪些LibraryTransaction函數返回promise。 但我認為您想要這樣的事情：

checkUserId(user_email)
    .then(info => {
        return changeBookStatus(bookInfo._id, borrow)
            // This is here so we can return "info" to the next function. You might want to
            // wrap this "changeBookStatus(...).then(...)" part in its own function.
            .then(() => {
                return info;
            });
    })
    .then(info => {
        return issueReturnBook(info._id, bookInfo._id, due_date + "/" + due_month, borrow);
    })
    .then(savedInfo => {
        console.log("saved info " + savedInfo._id);
        LibraryTransaction
            .findById(savedInfo._id)
            .populate('UserDetails')
            .populate('BookDetails').exec((err, libInfo) => {
                res.json({
                    status: '200',
                    message: 'transaction completed',
                    data: libInfo
                });
            });

    })
    .catch(err => {
        res.json({
            status: '500',
            message: err
        });
    });

請注意，我已包含return語句，以明確說明每個promise必須返回才能正確鏈接。 但是您可以刪除它們來清理它們：

checkUserId(user_email)
    // The extra ".then" is still here for the reasons mentioned above
    .then(info => changeBookStatus(bookInfo._id, borrow).then(() => info))
    .then(info => issueReturnBook(info._id, bookInfo._id, due_date + "/" + due_month, borrow))
    .then(savedInfo => {
        console.log("saved info " + savedInfo._id);
        LibraryTransaction
            .findById(savedInfo._id).
            populate('UserDetails')
            .populate('BookDetails').exec((err, libInfo) => {
                res.json({
                    status: '200',
                    message: 'transaction completed',
                    data: libInfo
                });
            });

    })
    .catch(err => {
        res.json({
            status: '500',
            message: err
        });
    });