问题

I want to add new row in exist csv file? if csv file exist, then i don't want to add column header and just want to add new row after exist row in the file.

Here is code which I'm trying:

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);
  }
});

回答1:

The following code will do what you asked:

When run the first time- will write the headers

Each run after that - will append json the data to the csv file

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,
    hasCSVColumnTitle: 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');
        });
    }
});

回答2:

Use csv-write-stream function to append data in csv file.

https://www.npmjs.com/package/csv-write-stream Add this line,with flag "a"

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

回答3:

using 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);
            }
        });
    });
}

回答4:

Seems, latest version of json2csv has dedicated method called .parse() to convert JSON to CSV compatible string. I tried json2csv.parse() converter and it works for me.

Common Issue:

I found a common issue in the solutions given here. The solutions don't append data without HEADER if we run the method multiple times.

Solution:

I used the header boolean option provided by json2csv to fix the issue. If we parse with {header:false} option we will get data as rows.

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

Below is the code that works exactly I mentioned above:

Example Code:

Below is the code sample:

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");
}

Calling `Write` Function

We have 3 parameters:

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'
    }];

Now calling the function write: