cannot send response out of db.query

Question

router.get('/detalle/(:id)', (req, res) => {
    let vehiculo_base
    db.query("select b.nombre, count(b.nombre) AS n_vehiculos from base AS b, vehiculo AS v where b.id = v.id_base AND b.id_flota = " + req.params.id , function(err, result){
        if (err) throw err
        vehiculo_base = result
    })
    res.send(vehiculo_base)
})

I want to add multiple query results to the response, but the variable vehiculo_base is undefined out of db.query

Does this answer your question? [How do I return the response from an asynchronous call?](https://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call) — Edric, Sep 27 '22 at 09:03

noitse · Answer 1 · 2022-09-27T08:56:14.203

The problem is that query is async, and you are returning the result with res.send right after executing it synchronously.

You should return the result once it is available.

router.get('/detalle/(:id)', (req, res) => {
    db.query("select b.nombre, count(b.nombre) AS n_vehiculos from base AS b, vehiculo AS v where b.id = v.id_base AND b.id_flota = " + req.params.id , function(err, result){
        if (err) throw err
        res.send(result)
    })
    
})

You should add logs in the future to understand the flow, and read a bit about async and sync execution. And how javascript execution works.

score 0 · Answer 2 · answered Sep 27 '22 at 08:45

db.query is async function so try like this.

router.get('/detalle/(:id)', (req, res) => {
    let vehiculo_base
    db.query("select b.nombre, count(b.nombre) AS n_vehiculos from base AS b, vehiculo AS v where b.id = v.id_base AND b.id_flota = " + req.params.id , function(err, result){
        if (err) throw err
        vehiculo_base = result
        res.send(vehiculo_base)
    })
})

second approach

router.get('/detalle/(:id)', async (req, res) => {
      let vehiculo_base
      var vehiculo_base = await db.query("select b.nombre, count(b.nombre) AS n_vehiculos from base AS b, vehiculo AS v where b.id = v.id_base AND b.id_flota = " + req.params.id);
       res.send(vehiculo_base)
  })

Hi, only the second option should work for me but this happens: TypeError: Converting circular structure to JSON --> starting at object with constructor 'Query' | property '_timer' -> object with constructor 'Timer' --- property '_object' closes the circle Do you know what this means and how could I fix it? — Castas115, Sep 29 '22 at 08:13

score 0 · Answer 3 · answered Sep 27 '22 at 08:45

You can rewrite this route as

router.get('/detalle/(:id)', async (req, res) => {
  try{
    let vehiculo_base = await 
    db.query("select b.nombre, count(b.nombre) AS n_vehiculos from base AS b, vehiculo AS v where b.id = v.id_base AND b.id_flota = " + req.params.id)
    res.send(vehiculo_base);
  }catch(error){
    res.send(error);
  }   
});

cannot send response out of db.query

3 Answers3