Node.js - PostgreSQL (pg) : Client has already been connected. You cannot reuse a client

问题

I am just trying to write simple register/login system. I am trying to find if username exists. Here is the steps :

Go localhost:3000/users/register page
Fill in all fields and click register button
Checking my command line if username exists it should print it with console.log

Everything works fine until now.

When I go back to the register page, I fill in all fields again and click register button. Then it throws it in command line :

Error: Client has already been connected. You cannot reuse a client.
at Client._connect (C:\Users\Hasan\Desktop\Projeler\node-ogreniyorum\node_modules\pg\lib\client.js:91:17)
at C:\Users\Hasan\Desktop\Projeler\node-ogreniyorum\node_modules\pg\lib\client.js:310:10
at new Promise (<anonymous>)
at Client.connect (C:\Users\Hasan\Desktop\Projeler\node-ogreniyorum\node_modules\pg\lib\client.js:309:10)
at Object.module.exports.findUserById (C:\Users\Hasan\Desktop\Projeler\node-ogreniyorum\database\register_sql.js:8:22)
at C:\Users\Hasan\Desktop\Projeler\node-ogreniyorum\routes\users.js:37:29
at Layer.handle [as handle_request] (C:\Users\Hasan\Desktop\Projeler\node-ogreniyorum\node_modules\express\lib\router\layer.js:95:5)
at next (C:\Users\Hasan\Desktop\Projeler\node-ogreniyorum\node_modules\express\lib\router\route.js:137:13)
at next (C:\Users\Hasan\Desktop\Projeler\node-ogreniyorum\node_modules\express\lib\router\route.js:131:14)
at Route.dispatch (C:\Users\Hasan\Desktop\Projeler\node-ogreniyorum\node_modules\express\lib\router\route.js:112:3)

I dont understand because I already end my client after I call my method.

register_sql.js :


module.exports.findUserById =(async (username) =>{
    try {
        await client.connect();
        console.log('Connected successfuly');
        const result = await client.query("select * from users where username = ($1)", [username]);
        console.log(result.rows[0]['username']);
        await client.end();
        console.log('Client disconnected...');
    } catch (err) {
        console.log(err);
    }
});

I call register_sql.js in users.js. Here is users.js :

const router = express.Router();
const registerSQL = require('../database/register_sql');
router.route('/register')
    .get((req, res, next) => {
        res.render('register');
    })
    .post((req, res, next) => {
            const {
                username,
                password,
                password2
            } = req.body;
            let errors = [];
            if (!username || !password || !password2) {
                errors.push("Please fill in all fields!");
            }
            if (password != password2) {
                errors.push("Passwords do not match!");
            }
            if (password.length < 6) {
                errors.push("Password has to be at least 6 characters!");
            }
            if (errors.length > 0) {
                res.render('register', {
                    errors
                });
            } else {
                registerSQL.findUserById(username);
                res.redirect('/');
            }
});

module.exports = router;

Thank you for helping!

回答1:

With node-postgres (which is the one you're using) I've only made it work using the pool do manage the connections.

const pg = require('pg')
const pool = new pg.Pool();

pool.connect(function(err, client, done) {
    if(err) {
      return console.error('connexion error', err);
    }
    client.query("select * from users where username = ($1)", [username], function(err, result) {
      // call `done()` to release the client back to the pool
      done();
  
      if(err) {
        return console.error('error running query', err);
      }
      console.log(result.rows[0]['username'])
    });
});

来源：https://stackoverflow.com/questions/63074649/node-js-postgresql-pg-client-has-already-been-connected-you-cannot-reuse

标签

javascript

node.js

postgresql

express

node-postgres