Correct way to use async postgres in nodejs/express?

Question

The docs on https://node-postgres.com/guides/async-express give the example of:

const { Pool } = require('pg')
const pool = new Pool()
module.exports = {
  query: (text, params) => pool.query(text, params),
}

My DB code is effectively the same, with some added logging:

const { Pool } = require('pg')

var config = {
  user: process.env.DB_USER,
  database: process.env.DB,
  password: process.env.DB_PASSWORD,
  host: process.env.DB_HOST,
  port: process.env.DB_PORT,
  max: 10,
  idleTimeoutMillis: 30000,
};

const pool = new Pool(config);
module.exports = {
  query: (text, params) => {
    console.log(`sql: ${text}, params: ${params}`);
    return pool.query(text, params);
  }
}

This works fine when called with:

const result = await db.query('SELECT * FROM users WHERE email = $1 AND password = $2;', 
                              [req.body.email, req.body.password]);

When I make a mistake in my SQL, I get the warning:

(node:6345) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:6345) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
POST /verify - - ms - -
post /verify
(node:6345) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'id' of undefined
    at router.post (/home/fadedbee/myapp/routes/index.js:93:58)
    ...
    at router (/home/fadedbee/myapp/node_modules/express/lib/router/index.js:47:12)
(node:6345) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 2)

In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code. is what worries me.

How should I change my DB code fix this?

Matt · Accepted Answer · 2021-02-17 08:42:31Z

No functional difference to selfagencies answer, but in regards to the "lots of noise"... The repeated error handling code can be pulled out into a helper that loads your handlers and does any of the common request/response work.

async function myHandler(req, res){ 
  const query = 'SELECT * FROM users WHERE email = $1 AND password = $2;'
  return db.query(query, [ req.body.email, req.body.password ]);
})

function loadRoute(handlerFunction){
  return async function routeLoaderHelper(req, res, next){
    try {
      const res = await handlerFunction(req, res, next)
      // or templatey handling can go here too
      res.json({ data: res })
    }
    catch (error) {
      console.error(error)
      res.status(error.status || 500).json({ error })
    }
  }
}

app.post('/whatever', loadRoute(myHandler))

or use koa, which is the "async" express.

selfagency · Accepted Answer · 2021-02-17 06:36:13Z

1

You need to wrap your await in a try/catch block and handle the error.

const query = 'SELECT * FROM users WHERE email = $1 AND password = $2;';

try {
  const result = await db.query(query, [req.body.email, req.body.password]);
  
  // do something with result
} catch(error) {
  console.error(error)
}

answered Feb 17, 2021 at 6:36

selfagency

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2 Comments

fadedbee Over a year ago

Thanks for your answer. Adding try/catch blocks to dozens of queries is a lot of noise. I assume that I can't add the try/catch inside of query(). Is there a (central) way that I can make express return a 500 if any error is thrown?

selfagency Over a year ago

You can wrap the entire algorithm in a try/catch and not just the individual db calls, but you're going to have a harder time with specific error handling methods.

fadedbee · Accepted Answer · 2021-02-22 10:53:19Z

0

Running:

npm install express-promise-router --save

and then changing the top of my routes/index.js from:

const express = require('express');
const router = express.Router();

to:

const router = require("express-promise-router")();

Fixed the problem nicely. I now get an error page, with a stack trace during development.

I have not needed to add any try { blocks or wrapper functions.

edited Feb 22, 2021 at 10:53

answered Feb 17, 2021 at 19:37

fadedbee

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1 Comment

Matt Over a year ago

The express-promise-router wrapper implementation houses the promise rejection handler

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