Promise不会等待传递给下一个函数

Question

I am trying to insert all transactions into a database after I've parsed them. I have a function called load.newload(transactionlist); which is passed after baby parse finishes parsing.

I've tested my code, and it loads all the files if the file list is short, but once it gets long (around 10 files or more), it calls the load.newload(transactionlist) function even before it finished parsing.

I was thinking maybe I should have another promise for the baby.parse function, but it doesn't seem to work.

Results look like this:

parse file1, parse file2, parse file3, SQL connected, Insert data successful, parse file4, parse file5

How can I fix this?

This is my code:

var baby = require('babyparse');
var read = require('read-file');
var Promise = require('promise');
var load = require('../sql/insert');
var transactionlist = [];
var incomingfile = function(file){
     //async load file and then parse after loading
        var promise = new Promise(function (resolve, reject) {
              read( file, 'utf8', function (err, res){
              if (err) 
                {reject(err);
                console.log('Oops, an error occured while parsing the data: %s', err);}
              else {resolve(res);
                    console.log(file);}
            });
        }).then(function (results){
                var promise = new Promise(function (resolve, reject) {
                baby.parse(results , {
                    dynamicTyping: true,
                    delimiter: "|",
                    complete: function (results, error) {
                        if(error)
                        {console.log('Something went wrong');
                         reject(error);}
                        else {
                              for(i = 1; i < results.data.length - 1; i++)
                                {
                                    var transaction  = {
                                        column1 : results.data[i][14].substring(0, 6),
                                        column2: results.data[i][2].split(' ').join(''),
                                        column3: results.data[i][14].split(' ').join(''),
                                        column4: results.data[i][8],
                                        column5: results.data[i][9]
                                    }
                                    transactionlist.push(transaction);
                                }//end for loop
                                resolve(results);
                                }
                        //console.log("Finished:", JSON.stringify(results.data));
                    }//end baby parse complete:function
                    });//end baby parse function
                }).then(function (results){
                    load.newload(transactionlist);
            });//end inner .then function
        });//end .then function
}//end incoming file function


exports.incomingfile = incomingfile;


//newload function in insert.js
const sql = require('mssql/msnodesqlv8');
var config = require('../connect');
var newload = function (transactionlist){
            sql.connect(config)
              .then(() => {
                console.log('connected');
                    const table = new sql.Table('settlement');
                    table.create = true;
                    //table.columns.add('transactionid', sql.Int, { nullable: false, primary: true});
                    table.columns.add('colum1', sql.VarChar(6), { nullable: false });
                    table.columns.add('column2', sql.VarChar(50), { nullable: false });
                    table.columns.add('column3', sql.VarChar(50), { nullable: false });
                    table.columns.add('column4', sql.VarChar(50), { nullable: false });
                    table.columns.add('column5', sql.VarChar(5), { nullable: false });

                     //add here rows to insert into the table
                    for (i = 0; i < transactionlist.length; i++) {

                        table.rows.add(transactionlist[i].column1, transactionlist[i].column2, transactionlist[i].column3, transactionlist[i].column4, transactionlist[i].column5);
                        console.log('transaction list', i , JSON.stringify(transactionlist.length));
                      }     
                const request = new sql.Request();
                console.log('Ready to insert data');
                request.bulk(table, function (error, results){
                    if(error)
                    {
                        console.log('Something went wrong while inserting the data into the database');
                        sql.close();
                    }
                    else {
                        console.log('Data has been inserted successfully');
                        sql.close();
                    }
                })  
              });
};

exports.newload = newload;

Answer 1

The problem could be due to using a global variable transactionlist to share data among promises. Given its a case of chained promises, a better way to handle data transactionlist could be to pass it along with return statement and let the next promise handle it without ambiguity (that it was updated or not).

This is how I'd do a chained promise.

var baby = require('babyparse');
var read = require('read-file');
var Promise = require('promise');
var load = require('../sql/insert');
// var transactionlist = [];
var incomingfile = function(file){
     //async load file and then parse after loading
        var promise = new Promise(function (resolve, reject) {
              read( file, 'utf8', function (err, res){
              if (err) 
                {
                    reject(err);
                    console.log('Oops, an error occured while parsing the data: %s', err);
                }
              else {
                    resolve(res);
                    console.log(file);
               }
            });
        }).then(function (results){
                var promise = new Promise(function (resolve, reject) {
                baby.parse(results , {
                    dynamicTyping: true,
                    delimiter: "|",
                    complete: function (results, error) {
                        if(error)
                        {
                            console.log('Something went wrong');
                            reject(error);
                        }
                        else {
// define a local var here 
var transactionlist = [];

                                    for(i = 1; i < results.data.length - 1; i++)
                                {
                                    var transaction  = {
                                        column1 : results.data[i][14].substring(0, 6),
                                        column2: results.data[i][2].split(' ').join(''),
                                        column3: results.data[i][14].split(' ').join(''),
                                        column4: results.data[i][8],
                                        column5: results.data[i][9]
                                    }
                                transactionlist.push(transaction);

                                }//end for loop
// return transactionlist instead of updating global var
                                resolve([results, transactionlist]);
                                }
                        //console.log("Finished:", JSON.stringify(results.data));
                    }//end baby parse complete:function
                    });//end baby parse function
                }).then(function (results){
// load transactionlist again from passed values
var transactionlist = results[1];
results = results[0];
                    load.newload(transactionlist);
            });//end inner .then function
        });//end .then function
}//end incoming file function

I hope you can see the changes I made (they are not indented properly and commented). Using this method, you'd never miss data while using callbacks / promises.