如何在nodejs json2csv中的现有csv文件中追加新行？

Posted 2023-03-07

【中文标题】如何在nodejs json2csv中的现有csv文件中追加新行？

【英文标题】：How to append new row in exist csv file in nodejs json2csv?

【发布时间】：2017-04-05 04:33:19

【问题描述】：

我想在现有的 csv 文件中添加新行？如果 csv 文件存在，那么我不想添加列标题，只想在文件中存在的行之后添加新行。

这是我正在尝试的代码：

var fields = ['total', 'results[0].name.val'];
var fieldNames = ['Total', 'Name'];

var opts1 = 
  data: data,
  fields: fields,
  fieldNames: fieldNames,
  newLine: '\r\n'

;

var opts2 = 
  newLine: '\r\n',
  data: data,
  fields: fields,
  fieldNames: fieldNames,
  hasCSVColumnTitle: false,

;

fs.stat('file.csv', function (err, stat) 
  if (err == null) 
    console.log('File exists');
    var csv = json2csv(opts2);
    fs.appendFile('file.csv', csv, function (err) 
      if (err) throw err;
      console.log('The "data to append" was appended to file!');
    );
   else if (err.code == 'ENOENT') 
    // file does not exist
    var csv = json2csv(opts1);
    fs.writeFile('file.csv', csv, function (err) 
      if (err) throw err;
      console.log('file saved');
    );
   else 
    console.log('Some other error: ', err.code);
  
);

【问题讨论】：

那么问题出在哪里？

如何在现有的 csv 文件中追加新行？

你已经有代码来检查文件是否已经存在。现在只是 append a new row. CSV 只是意味着“逗号分隔值”。以这种方式格式化数据非常容易。

谢谢。它的工作。但是如何在 csv 文件中添加新行。我尝试使用 \t\n 命令，但没有按预期工作。

你为什么要使用\t？这就是一个标签。你需要做\n（或\r\n），然后是你的新行。例如：'\n' + row.

【参考方案1】：

以下代码将按照您的要求进行：

第一次运行时 - 将写入标头 之后的每次运行 - 都会将 json 数据附加到 csv 文件中

var fs = require('fs');
var json2csv = require('json2csv');
var newLine = '\r\n';

var fields = ['Total', 'Name'];

var appendThis = [
  
    Total: '100',
    Name: 'myName1',
  ,
  
    Total: '200',
    Name: 'myName2',
  ,
];

var toCsv = 
  data: appendThis,
  fields: fields,
  header: false,
;

fs.stat('file.csv', function (err, stat) 
  if (err == null) 
    console.log('File exists');

    //write the actual data and end with newline
    var csv = json2csv(toCsv) + newLine;

    fs.appendFile('file.csv', csv, function (err) 
      if (err) throw err;
      console.log('The "data to append" was appended to file!');
    );
   else 
    //write the headers and newline
    console.log('New file, just writing headers');
    fields = fields + newLine;

    fs.writeFile('file.csv', fields, function (err) 
      if (err) throw err;
      console.log('file saved');
    );
  
);

【参考方案2】：

似乎，最新版本的json2csv 有一个名为.parse() 的专用方法来将JSON 转换为CSV 兼容字符串。我尝试了json2csv.parse() 转换器，它对我有用。

常见问题：

我在此处给出的解决方案中发现了一个常见问题。如果我们多次运行该方法，则解决方案不会在没有 HEADER 的情况下附加数据。

解决方案：

我使用json2csv 提供的header 布尔选项来解决此问题。如果我们使用header:false 选项解析，我们将获取数据作为行。

// Rows without headers.
rows = json2csv(data,  header: false );

下面是我上面提到的代码：

示例代码：

下面是代码示例：

const fs = require('fs');
const path = require('path');
const json2csv = require('json2csv').parse;
const write = async (fileName, fields, data) => 
    // output file in the same folder
    const filename = path.join(__dirname, 'CSV', `$fileName`);
    let rows;
    // If file doesn't exist, we will create new file and add rows with headers.    
    if (!fs.existsSync(filename)) 
        rows = json2csv(data,  header: true );
     else 
        // Rows without headers.
        rows = json2csv(data,  header: false );
    

    // Append file function can create new file too.
    fs.appendFileSync(filename, rows);
    // Always add new line if file already exists.
    fs.appendFileSync(filename, "\r\n");

调用Write函数

我们有 3 个参数：

fields = ['Name', 'Position', 'Salary'];
    data = [
        'Name': 'Test1',
        'Position': 'Manager',
        'Salary': '$10500'
    ,
    
        'Name': 'Test2',
        'Position': 'Tester',
        'Salary': '$5500'
    , 
        'Name': 'Test3',
        'Position': 'Developer',
        'Salary': '$5500'
    , 
        'Name': 'Test4',
        'Position': 'Team Lead',
        'Salary': '$7500'
    ];

现在调用函数write：

write('test.csv', fields, data);

每次我们调用上述方法时，它都会从新行开始写入。如果文件不存在，它只会写入一次标题。

【参考方案3】：

我对函数的行为方式进行了一些更改，现在我使用 2 种方法验证是否有标题，如果存在，我忽略它并添加行，如果没有，我添加标题，从对象中删除引号并传递一些等待，因为它是同步的功能并且没有等待所以异步没有意义哈哈哈

传递给 filename 的 CSV 值是节点将在项目根目录中查找以保存最终文档的文件夹的名称

??

Fiz umas mudanças em como a função se comporta, agora eu valido com 2 métodos se existe cabeçalho, se existir eu ignoro ele e adiciono as rows, se não eu adiciono o cabeçalho, removi as aspas dos objetos e passe uns awaits, porque a função era sync e não tinha nenhum await então não fazia sentido ser async haha​​ha

O valor CSV passado para o nome do arquivo é o nome da Pasta que o nó procurará na raiz do projeto para salvar seu documento final

const fs = require("fs");
const path = require("path");
const json2csv = require("json2csv").parse;

// Constructor method to assist our ReadFileSync
const readFileSync = filePath =>
  fs.readFileSync(filePath,  encoding: "utf-8" );

// A helper to search for values ​​in files =D
const findWord = async (text, filePath) => 
  const result = await readFileSync(path.join(__dirname, filePath));
  return Promise.resolve(RegExp("\\b" + text + "\\b").test(result));
;

const write = async (fileName, fields, data) => 
  // output file in the same folder
  const filename = path.join(__dirname, "CSV", `$fileName`);
  let rows;

  // I check if there is a header with these items
  const hasValue = await findWord("Name,Position,Salary", "./CSV/test.csv");
//  If there is a header I add the other lines without it if I don't follow the natural flow
  if (hasValue) 
    rows = json2csv(data,  header: false );
   else if (!fs.existsSync(fields)) 
  // If file doesn't exist, we will create new file and add rows with headers.
    rows = json2csv(data,  header: true );
   else 
    // Rows without headers.
    rows = json2csv(data,  header: false );
  

  // I deal with the information by removing the quotes
  const newRows = rows.replace(/[\\"]/g, "");
  // Append file function can create new file too.
  await fs.appendFileSync(filename, newRows);
  // Always add new line if file already exists.
  await fs.appendFileSync(filename, "\r\n");
;

fields = ["Name", "Position", "Salary"];
data = [
  
    Name: "Test1",
    Position: "Manager",
    Salary: "$10500",
  ,
  
    Name: "Test2",
    Position: "Tester",
    Salary: "$5500",
  ,
  
    Name: "Test3",
    Position: "Developer",
    Salary: "$5500",
  ,
  
    Name: "Test4",
    Position: "Team Lead",
    Salary: "$7500",
  ,
];

write("test.csv", fields, data);


Output:
"Name","Position","Salary"
"Test1","Manager","$10500"
"Test2","Tester","$5500"
"Test3","Developer","$5500"
"Test4","Team Lead","$7500"

【参考方案4】：

使用 csv-write-stream 函数将数据追加到 csv 文件中。

https://www.npmjs.com/package/csv-write-stream 添加这一行，带有标志“a”

writer.pipe(fs.createWriteStream('out.csv', flags: 'a'))

【参考方案5】：

使用json-2-csv:

/**
 *  this function will create the file if not exists or append the 
 *   data if exists
 */

function exportToCsvFile(headersArray, dataJsonArray, filename) 

    converter.json2csvAsync(dataJsonArray, prependHeader: false).then(function (csv) 

    fs.exists(filename + '.csv', async function (exists) 

        if (!exists) 
            var newLine = "\r\n";
            var headers = ((headersArray ? headersArray : []) + newLine);

            exists= await createFileAsync(filename+ '.csv', headers);
        

        if (exists) 
            fs.appendFile(filename + '.csv', csv, 'utf8', function (err) 
                if (err) 
                    console.log('error csv file either not saved or corrupted file saved.');
                 else 
                    console.log(filename + '.csv file appended successfully!');
                
            );
        
    );
).catch(function (err) 
    console.log("error while converting from json to csv: " + err);
    return false;
);



function createFileAsync(filename, content) 
    return new Promise(function (resolve, reject) 
        fs.writeFile(filename, content, 'utf8', function (err) 
            if (err) 
                console.log('error '+filename +' file either not saved or corrupted file saved.');
                resolve(0);
             else 
                console.log(filename + ' file created successfully!');
                resolve(1);
            
        );
    );