第一个请求发送抛出服务器错误500

Question

使用nodejs进行开发并发送表单提交的发布请求时，第一个请求会引发服务器错误500，但后续单击按钮可以正常工作。以下是我的代码。我做错了什么？

的Ajax

$(document).ready(function (e) {
$("#group_ledger_form").on('submit',(function(e) {
e.preventDefault();
var data = {};
data.group_ledger_name = $('#group_ledger_name').val();
data.group_ledger_type = $('#group_ledger_type').val();
$('#loading').show();
$.ajax({
    url: "/group-ledger", 
    type: "POST",  
    data: data, 
    dataType: 'json',
   cache: false,             
   processData:true,    
   success: function(data)
   {
        if( data.status == '500' ) {
         console.log('error occured');
      } else {
      $('#loading').hide();
        }
    }
});
}));
});

group_ledger.js

var express      = require('express');
var router       = express.Router();
var db           = require('./../db');
var chart_func   = require('./../chart-of-accounts');

router.post('/', function(req, res, next) {
    var group_ledger_name      = req.body.group_ledger_name;
    var group_ledger_type      = req.body.group_ledger_type;
    chart_func.allChartsByAccountName(group_ledger_name).then(function(pre_rows){
        for (var i = 0; i < pre_rows.length; i++) {
            pre_account_name = pre_rows[i]['account_name'];
         }

     });

console.log(pre_account_name);
 });

module.exports = router;

app.js

var express      = require('express');
var path         = require('path');
var favicon      = require('serve-favicon');
var logger       = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser   = require('body-parser');
var mysql        = require('mysql');
var db           = require('./db');

var routes                    = require('./routes/index');
var chart_of_accounts         = require('./routes/chart_of_accounts');
var group_ledger              = require('./routes/group_ledger');



var app = express();
// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'ejs');

app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));
app.use('/', routes);
app.use('/chart-of-accounts', chart_of_accounts);
app.use('/group-ledger', group_ledger);


// catch 404 and forward to error handler
app.use(function(req, res, next) {
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});

// error handlers

// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
  app.use(function(err, req, res, next) {
    res.status(err.status || 500);
    res.render('error', {
      message: err.message,
      error: err
    });
  });
}

// production error handler
// no stacktraces leaked to user
app.use(function(err, req, res, next) {
  res.status(err.status || 500);
  res.render('error', {
    message: err.message,
    error: {}
  });
});


module.exports = app;