How can I implement the output of the ID from the database to a variable?

Question

MySQL

pool.getConnection(function(err, connect) {

            connect.query('SELECT * FROM users WHERE vkontakteid = ?', [req.user.id], function(err, result) {

                if (err) console.log(err);

                else {
                    if (result.length === 0) {
                        const data = [req.user.id, req.user.displayName]
                        connect.execute('INSERT INTO users (vkontakteid, name) VALUES (?,?)', data)
                        console.log('Вы были зарегистрированы')
                    } else {
                        const data = [req.user.displayName, req.user.id];
                        connect.execute('UPDATE users SET name=? WHERE vkontakteid=?', data)
                        console.log('Такой пользователь уже существует')
                        console.log(result)
                    }
                }

            }, pool.releaseConnection(connect))
        })
        res.redirect('/')

Is it possible to somehow output this id to a variable?

Answer 1

You can just create a variable before calling getConnection

let id;
pool.getConnection(function(err, connect) {
    connect.query(..., function(err, result) {
        ...
        if(!err && result.length !== 0) {
            id = result.id;
        }
        ...
    }
}

But due to the fact that queries to the database are asynchronous, you will not be able to find out when the value is written to the variable.
For this reason, a callback is passed to asynchronous functions, which will receive the result of executing asynchronous code as input.

function createOrUpdateUsersCallback(err, result) {
    if (err) {
    console.log(err);
  }
  else {
    // Use result.id as you want
  }
}

function createOrUpdateUsers(callback) {
  pool.getConnection(function(err, connect) {
    connect.query(..., function(err, result) {
      if(err) {
        callback(err, null);
      }
      else {
        // Do create or update 
        callback(null, result);
      }

    }
  }
}

createOrUpdateUsers(createOrUpdateUsersCallback);

But in the modern world, the easiest way to work with asynchronous code is through promises and async / await
. On promises, it will be something like

const createOrUpdateUsersPromise = new Promise((resolve, reject) => {
  function createOrUpdateUsers(callback) {
    pool.getConnection(function(err, connect) {
      connect.query(..., function(err, result) {
        if(err) {
          reject(err);
        }
        else {
          // Do create or update 
          resolve(result);
        }

      }
    }
  }
})

const result = await createOrUpdateUsersPromise();
const id = result.id;