使用node.js + mysql的最后一个insertId的全局范围

Question

I am calling function in order to insert some values into a database table using mysql module of node.js . The function is called inside a for loop and I can get the last insertId of each INSERT query inside the function.

MY PURPOSE

I want to store these id's to an array in to order to use them later in my code but I cannot do that.

- FUNCTION CALL

 for(var i=0;i<some_number;i++){
   if (<something is true>){

  var lastid = [];
  //Function calling
  function_a(x, y, z, w,  function(error, result) {
   if(!error){
       lastid.push(result.insertId);
       }
   //To Do
   else{}
  });
 }
}

- FUNCTION

function function_a(a, b, c, d, callback){
//Connection to the DB
const con = mysql.createConnection({
  host: 'host',
  user: 'user',
  password: 'password',
  database: 'database'
});

//DB query
var query = "INSERT INTO my_table (column1, column1, column1, column1) VALUES ('"+a+"', '"+b+"', '"+c+"', '"+d+"')";
con.query(query, (err, rows) => {
 var e = rows.insertId;
 return callback(err, e);
});
con.end(); 
}

The problem is that I cannot use the id's outside the function.

Any idea how can I do that?Is this about variable scope?

Answer 1

Several problems here, and yes, they are partly about variable scope.

Put var lastid = []; before the for loop, so you can use it after the loop. However, as you have callback mechanism inside the loop, you must wait for the whole loop to finish (all callbacks called from 0 to some_number-1 , in order to have the right values in lastid array. It's a messy thing with callbacks, but you can do it with them or with promises. You can Google for callback handling in for loops.

Answer 2

The function function_a is a asynchronous function. In your case you can use async module to do this task:

var taskIds = Array.apply(null, {length: some_number}).map(Number.call, Number);
var lastid = [];
async.eachLimit(taskIds, 32, function (taskId, done) {
  if (<something is true>) {
    function_a(x, y, z, w,  function(error, result) {
      if(!error){
        lastid.push(result.insertId);
      }
      //To Do
      else{}
      done()
    });
  } else {
    done()
  }
}, function () { 
  // Do some thing with lastid
  console.log(lastid);
});