getting values from sqlite database and store in an array -Nodejs-CodePudding

I want to store the information in the SQLite database in arrays. When I write it as below, the output is undefined.

let hostnames = [];
let usernames = [];
let passwords = [];
let commands = [];
let status = [];
let ids = [];
let mac = [];
 
//read from sqlite

var sqlite3=require('sqlite3').verbose();

var db=new sqlite3.Database('../database/database.sqlite',(err)=>{
    if(err){
        return console.error(err.message);
    }
    console.log('Connected...');
});

db.all('SELECT * FROM Users ORDER BY id',[],(err,rows)=>{
    if(err){
        return console.error(err.message);
    }
    rows.forEach((row)=>{
        
       hostnames.push(row.name);
       usernames.push(row.username);
       passwords.push(row.password);
       commands.push(row.command);
       status.push(row.status);
       mac.push(row.mac);
       ids.push(row.id);
       
    
       
    });
});

console.log("hostnames",hostnames);

When I want to reach hostnames from outside the forEach; console.log("hostnames",hostnames); the console output is undefined.I'm not sure how I should do it. I would be glad if you help

CodePudding user response：

It's not working because this is asynchronous code. It must have callback such that it responds after the database query finishes.

documentation: https://nodejs.org/en/knowledge/getting-started/control-flow/what-are-callbacks/

example

In this example I’m passing a callback to the function DataExt and calling it after it finishes.

let hostnames = [];

var sqlite3=require('sqlite3').verbose();


function DataExt(db, callback) {
    db.all('SELECT * FROM Users ORDER BY id',[],(err,rows)=>{
        if(err){
            return console.error(err.message);
        }
        else
        {           
            rows.forEach((row)=>{
                hostnames.push(row.name);
             });
            
            return callback(false, hostnames);
              
        }

    });
}

var db=new sqlite3.Database('../database/database.sqlite',(err)=>{
    if(err){
        return console.error(err.message);
    }
    console.log('Connected...');
});

DataExt(dtb, function(err, content) {
    if(err) throw(err);
    ExtractedHostnames = content;
    console.log("hostnames", ExtractedHostnames);
})