Question

我尝试通过解析器管道CSV文件，删除给定ID的行，将新数组传输到字符串，然后最终将结果输出到新的CSV。

问题是新数组未正确返回。我的意思是，我设法删除该行但不返回新的CSV。

以下是代码：

'use strict';


const Fs    = require('fs');
const Csv   = require('csv');


let input  = 'data_stack.csv';
let output = 'data_output.csv';


let readStream  = Fs.createReadStream(input);
let writeStream = Fs.createWriteStream(output);

let opt  = {delimiter: ',', quote: '"', escape: '"', relax: true, skip_empty_lines: true};

function deleteRow (id) {

    return Csv.parse(opt, (err, data) => {
        if (err) throw err;

        let delId = [];
        // The row corresponding to the id is pushed to an array to console.log it. The other rows are returned 
        let newData = data.filter(line => {
            if (line[0] === id) {
                delId.push(line);
            }
            else {
                return line;
            }
        });

        if (delId !== 0) {
            console.log("Deleted line\n");
            console.log(delId);
        }

        // Testing if the row was deleted
        let result = [];
        // If the row is not deleted, push it into the result array
        newData.forEach(line => {
            if (line[0] === id) {
                result.push(line);
            }
        });
        // "Not found !" is console logged. The row has been deleted 
        if (result.length !== 0) {
            console.log(result);
        }
        else {
            console.log("Not found !");
        }

        return newData;
    });
}

readStream.pipe(deleteRow('566150121ae803f53751c3f2'))

此代码正常运行但是如果我选择返回newData数组来管道一个字符串，然后将结果输出到CSV文件，我会得到2个意外的行为：

delId数组现在为空，我不知道为什么
创建了输出文件，但之前删除的行仍然存在于输出文件

以下是代码：

'use strict';


const Fs    = require('fs');
const Csv   = require('csv');


let input  = 'data_stack.csv';
let output = 'data_output.csv';


let readStream  = Fs.createReadStream(input);
let writeStream = Fs.createWriteStream(output);

let opt  = {delimiter: ',', quote: '"', escape: '"', relax: true, skip_empty_lines: true};

function deleteRow (id) {

    return Csv.parse(opt, (err, data) => {
        if (err) throw err;

        let delId = [];
        // The row corresponding to the id is pushed to an array to console.log it. The other rows are returned 
        let newData = data.filter(line => {
            if (line[0] === id) {
                delId.push(line);
            }
            else {
                return line;
            }
        });

        if (delId !== 0) {
            console.log("Deleted line\n");
            console.log(delId);
        }

        // Testing if the row was deleted
        let result = [];
        // If the row is not deleted, push it into the result array
        newData.forEach(line => {
            if (line[0] === id) {
                result.push(line);
            }
        });
        // "Not found !" is console logged. The row has been deleted 
        if (result.length !== 0) {
            console.log(result);
        }
        else {
            console.log("Not found !");
        }

        return newData;
    });
}

let stringifier = Csv.stringify({quoted: true});

readStream.pipe(deleteRow('566150121ae803f53751c3f2')).pipe(stringifier).pipe(writeStream);

我真的不明白来自deleteRow函数的结果如何影响它的行为。

有任何建议吗？

Answer 1

csv.parse有2 APIs：

基于回调（缓冲）和;
Streams based。

如果您传递回调函数，就像您在示例中所做的那样，您正在订阅回调API，这意味着您可以通过data参数获得整个解析后的数据。

但是，该回调是一个流'sink'，这意味着对数据的任何修改都不会归结为writeStream。

您需要调整代码以使用回调API，如下所示：

function deleteRow(readStream, id, done) {
  readStream.pipe(Csv.parse(opt, (err, data) => {
    if (err) return done(err);

    // Wrire new data to file
    Csv.stringify(data.filter(line => line[0] !== id))
      .pipe(writeStream)
      .on('end', done);
  }));
}

deleteRow(readStream, '5660d7e11ae803f53751aeb0', function (err) {
  console.log('done!');
});

或者，使用像这样的流API：

Node.js Stream API出现意外行为

1 个答案: