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After reading the docs: https://github.com/brianc/node-pg-pool, I am slightly concerned about reusing the new Pool() method.

The docs suggests that I need to place the new Pool() before exports and return it like so 

// db.js
const pool = new Pool();
module.exports = () => { return pool; }

This way I can reuse Pool until the idleTimeoutMillis or client.release(), by using require() from other files Eg: 

const connect = require('./db')
connect().query(' .... ');

If this is correct, how does it work? Does node.js caches the new Pool(), as it not inside module.exports?

Vao Tsun
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Antartica
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2 Answers2

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Yes, it is effectively cached since you create it exactly once (and node caches modules) and you always refer to that same instance in your exported method.

mscdex
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  • Thanks, so that means I should always export the result only without dependencies, etc... ? – Antartica Aug 21 '16 at 11:16
  • I don't understand your question. – mscdex Aug 21 '16 at 16:36
  • Sorry, actually after testing this code, I get `TypeError: connect.query is not a function`. It seems like the pool isn't initialized before `require()`. Do you know what's wrong? Reference: https://github.com/brianc/node-pg-pool#a-note-on-instances – Antartica Aug 21 '16 at 19:35
  • You're exporting a *function* that returns a db connection, so you'd need to do: `connect().query()`. – mscdex Aug 21 '16 at 20:55
  • Thanks, and what should I do to have `connect().query()` written as `connect.query()` , apart from doing this -> `const connect = connect();` – Antartica Aug 21 '16 at 21:20
  • You *could* export a function that calls `pool.connect().query(...)`, passing its arguments. – mscdex Aug 21 '16 at 22:59
  • last question... I could export `Pool()` like so `module.exports = new Pool()` (as an object). So should I `return` it as a function or use it as an object? What the best practice? – Antartica Aug 22 '16 at 00:53
  • I don't think there is a best practice, it's just whatever you find more convenient. – mscdex Aug 22 '16 at 01:27
  • @Atartica for a friendlier API that doesn't require connecting, see [pg-promise](https://github.com/vitaly-t/pg-promise) ;) – vitaly-t Aug 24 '16 at 18:14
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Absolutely, by creating the instance just once, you allow the node to cache it, and subsequently, you maintain a consistent reference to that identical instance within your exported method

Mubeen Siddiqui
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