我应该如何将同步node.js模块与mysql，套接字函数一起使用？

Question

I'm trying to understand and use sync-npm module, but not sure how to change my functions below to match sync format... ( https://www.npmjs.com/package/sync )

Basically I'm trying to use input data (which is formed as a list in client side) I receive from frontend(client) and send it to node.js via socket. I tried to store it in my global variable 'query', but I learned that it doesn't get updated. So when I tried to print 'query' outside of socket function, it doesn't work.

It sounds like I should use sync module, but I'm not quite sure how to implement that in my code...If anyone could give me an idea how to change my functions below, it would be great..thanks!

Receiving input data from frontend and sending it to node.js via socket

var server = app.listen(3001);
var socket = require('socket.io');
var io = socket(server);
var query = []

// Register a callback function to run when we have connection
io.sockets.on('connection',newConnection);
function newConnection(socket){
  console.log('new connection: ' + socket.id);
  socket.on('search', newSearch);
  function newSearch(final){
    query.push(final)

    console.log(query[0]);
    console.log(Array.isArray(query[0]));  //returns True
    console.log(query[0][0]);    // this also works
    console.log(query[0][1]);
  }
}
console.log('print');  
console.log(query);    
// this only gets printed in the beginning as an empty array

Ultimately, I'm parsing that list of input data and concat into my sql select phrase. Below is my DB portion code:

  var mysql      = require('mysql');
  var connection = mysql.createConnection({
    host     : '~~~',
    user     : '~~~',
    password : '~~~',
    database : '~~~'
  });

  connection.connect();
  console.log('mysql connected');

  var sql = 'select' + '*' + 'from EBN ';
  //ideally data in the 'query' list will concat with this sql string

  connection.query(sql,function(err,rows,fields){
    if(err){
      console.log(err);
    }
    else{
      fs.writeFileSync('search.json', JSON.stringify(rows), 'utf8');
    }
});

Answer 1

Firstly, you should wrap the code that does the query execution in a function, something like

 var mysql = require('mysql'); var connection = mysql.createConnection({ host : '~~~', user : '~~~', password : '~~~', database : '~~~' }); connection.connect(); console.log('mysql connected'); function executeQuery(query) var sql = 'select' + '*' + 'from EBN '; //do something with query and add it to the sql string connection.query(sql,function(err,rows,fields){ if(err){ console.log(err); } else{ fs.writeFileSync('search.json', JSON.stringify(rows), 'utf8'); } } } 

This is necessary because you don't want to execute a query right after starting the server, but only after you received the query message via socket. So now you can call executeQuery(final) in your socket message handler.

You should learn how asynchronous programming and callbacks works in nodejs/javascript, and why you should use it as much as possible for server applications (eg use fs.writeFile instead of writeFileSync ). You can use packages like sync to make life easier for you, but only when you know exactly what you want to do. Just throwing something with the name 'sync' in it at a problem that might be caused by asynchronicity is not going to work.