Question

我正在Node中使用ssh2-sftp-client下载一系列文件。下载文件后，我需要检查每个文件是否为CSV，然后检查我的数据库以查看文件是否先前已导入。

我正在使用Promise，但在排序时遇到了麻烦。我认为经过几个小时的研究，我已经接近了，但不能完全理解。

代码如下：

const isFileCSV = (filename) => {

    return new Promise( (resolve, reject) => {
        if (filename.endsWith('.csv')) {
            result = 'true';
            resolve(result);
        } else {
            result = 'false';
            resolve(result);
        }
    });
}

const wasFileImported = (filename) => {     
    // Return a new promise
    return new Promise( (resolve, reject) => {
        // Core function
        con.query(`CALL wasFileImported('${filename}')`, (err, results) => {
            console.log('02 Checking if file was previously imported.');    
            if (err) {
                logEntry('error', `Error searching database: ${err}`);
                reject(Error('false'));
            } else {
                result = results[0][0]['importCheck'];
                resolve(result);
            }
        })
    });
}

const importFile = (file) => {
    isFileCSV(file).then((result) => {
        console.log(`01a File ${file} ends with csv? ${result}`);
        result = result.toLowerCase();
        return result;
    }).then((result) => {
        if (result === 'false') {
            console.log(`01b ${result} = Not csv, log it and skip to next.`);
            return;
        } else if (result === 'true') {
            console.log(`01b ${result} = It is csv, go to next step`);
            return result;
        }
    }).then((result) => {
        wasFileImported('file').then((result) => {
            console.log('03 checked import, result: ', result);
            return result.toLowerCase();
        }).then((result) => {
            switch(result) {
                case 'false':
                    console.log('04a download file and log it');
                    break;
                case 'true':
                    console.log('04b skip it and log the skip');
                    break;
                default:
                    console.log('04c unknown error, log the skip');                         
            }           
        })              
    })              
}

logEntry('info', `attempting to connnect to ${config.destination.host}`);
console.log('00 start');

sftp.connect(crmConfig).then(() => {
    logEntry('info', `connected to ${config.destination.host}`);
    return sftp.list(ordersUrl);
}).then((data) => {
    fileList = [];
    Object.entries(data).forEach(([key, val]) => {
        fileList.push(val['name']);
    });
    return fileList;
}).then((fileList) => {
    let promises = [];

    fileList.forEach((file) => {
        promises.push(importFile(file));
    });

    Promise.all(promises).then(function(results) {
        console.log('Done');
    }).catch(function(err) {
        console.log('Error');
    });
});

我希望看到的是以下内容：

00 start
01a File daily.csv ends with csv? true
01b true = It is csv, go to next step
02 Checking if file was previously imported.
03 checked import, result:  FALSE
04a download file and log it
01a File daily072418.csv ends with csv? true
01b true = It is csv, go to next step
02 Checking if file was previously imported.
03 checked import, result:  FALSE
04a download file and log it
01a File test.csw ends with csv? false
01b false = Not csv, log it and skip to next.
02 Checking if file was previously imported.
03 checked import, result:  FALSE
04a download file and log it
Done

我实际上得到的是：

00 start
01a File daily.csv ends with csv? true
01a File daily072418.csv ends with csv? true
01a File test.csw ends with csv? false
01b true = It is csv, go to next step
01b true = It is csv, go to next step
01b false = Not csv, log it and skip to next.
Done
02 Checking if file was previously imported.
03 checked import, result:  FALSE
04a download file and log it
02 Checking if file was previously imported.
03 checked import, result:  FALSE
04a download file and log it
02 Checking if file was previously imported.
03 checked import, result:  FALSE
04a download file and log it

早期版本未使用Promise.all，但仍产生相同的结果。我还尝试过更改解决方案以返回wasFileImported和isFileCSV，但是随后我只得到“ 00 Start”，然后是“ Done”，之间没有执行。

很明显，我没有按照我的意图正确地遍历数组。做所有事情都是按顺序完成的最好方法是什么？

编辑对于其他需要它的人，这里是最终的工作代码，这要感谢@ jordan-peterson和@spakmad：

const isFileCSV = (filename) => {
    return new Promise( (resolve, reject) => {
        if (filename.endsWith('.csv')) {
            result = 'true';
            resolve(result);
        } else {
            result = 'false';
            resolve(result);
        }
    });
}

const wasFileImported = (filename) => {     
    // Return a new promise
    return new Promise( (resolve, reject) => {
        // Core function
        con.query(`CALL wasFileImported('${filename}')`, (err, results) => {
            console.log('02 Checking if file was previously imported.');    
            if (err) {
                logEntry('error', `Error searching database: ${err}`);
                reject(Error('false'));
            } else {
                result = results[0][0]['importCheck'];
                resolve(result);
            }
        })
    });
}

const importFile = (file) => {
    return isFileCSV(file).then((result) => {
        console.log(`01a File ${file} ends with csv? ${result}`);
        result = result.toLowerCase();
        return result;
    }).then((result) => {
        if (result === 'false') {
            console.log(`01b ${result} = Not csv, log it and skip to next.`);
            return;
        } else if (result === 'true') {
            console.log(`01b ${result} = It is csv, go to next step`);
            return result;
        }
    }).then((result) => {
        return wasFileImported('file').then((result) => {
            console.log('03 checked import, result: ', result);
            return result.toLowerCase();
        }).then((result) => {
            switch(result) {
                case 'false':
                    console.log('04a download file and log it');
                    break;
                case 'true':
                    console.log('04b skip it and log the skip');
                    break;
                default:
                    console.log('04c unknown error, log the skip');                         
            }           
        })              
    })              
}

console.log('00 start');

sftp.connect(crmConfig).then(() => {
    logEntry('info', `connected to ${config.destination.host}`);
    return sftp.list(ordersUrl);
}).then((data) => {
    fileList = [];
    Object.entries(data).forEach(([key, val]) => {
        fileList.push(val['name']);
    });
    return fileList;
}).then((fileList) => {
    let promiseChain = Promise.resolve()

    fileList.forEach((file) => {
        promiseChain = promiseChain.then(() => {
            return importFile(file)
        })
    })
});

Answer 1

您要连续三次调用importFile（一种异步方法），因此它会同时遍历这些方法。如果您要一个接一个地执行，我想做的就是这个。

let promiseChain = Promise.resolve()
myFiles.forEach((file) => {
   promiseChain = promiseChain.then(() => {
      return importFile(file)
   }
}

循环中的每次迭代都会将另一个then附加到Promise中的promiseChain，直到第一个then返回时才向前移动。附加的第一个then会立即前进，因为此时promiseChain是Promise.resolve()

这也可以用reduce完成。

myFiles.reduce((acc, file) => acc.then(() => importFiles(file))), Promise.resolve())

Answer 2

好像importFile没有返回承诺。这意味着承诺列表中充满了import re m = re.findall("=(.*?)=", "A =BC= D =EF=")。您可以使用[undefined, undefined...]进行检查。调试“打印所有东西！”的第一步。将return语句放在 console.log()。至少这就是为什么“完成”在中间。您的csv检查排在最前面的原因是因为它们不是异步的，因此您的代码在控制处理异步部分的代码之前首先要进行所有操作。

Answer 3

importFile必须是一个承诺，尝试一下：

const importFile = function(file){

    return new Promise(function(resolve, reject){

        isFileCSV(file).then((result) => {
            console.log(`01a File ${file} ends with csv? ${result}`);
            result = result.toLowerCase();

            if (result === 'false') {
                console.log(`01b ${result} = Not csv, log it and skip to next.`);
            } else if (result === 'true') {
                console.log(`01b ${result} = It is csv, go to next step`);
            }

            wasFileImported('file').then((result) => {
                console.log('03 checked import, result: ', result);

                switch(result) {
                    case 'false':
                        console.log('04a download file and log it');
                        break;
                    case 'true':
                        console.log('04b skip it and log the skip');
                        break;
                    default:
                        console.log('04c unknown error, log the skip');                         
                }

                return resolve(result);
            }) 

        });

    });     
}

等待对数组中每个项目的承诺

3 个答案: