Koa-pg Can't find module pg - node.js

Question

Hey so I'm trying to get Nodejs Koa to talk to postgres using the Koa-pg module, but I keep getting a 'Can't find module pg' error.
I've tried to follow the koa-pg examples, but have come up short...so any advice would on how to progress would be appreciated.
If created my app.js file as follows:
var koa = require('koa');
var route = require('koa-route');
var koaPg = require('koa-pg');
var roads = require('./controllers/roads');
var app = module.exports = koa();
app.use(route.get('/roads/bbox/', roads.bbox));
app.listen(3000);
console.log('listening on port 3000');
And then created my controller file as follows:
var credentials = require('../credentials.js');
var environment = credentials.dev;
app.use(koaPg('postgres://' + environment.user + '#' + environment.host + ':' + environment.port + '/' + environment.database))
module.exports.bbox = function * bbox(next) {
var result = yield this.koaPg.db.client.queryPromise('SELECT now()')
console.log('result: ', result)
this.body = result.rows[0].now.toISOString()
};
But I'm getting the following error:
module.js:338
throw err;
^
Error: Cannot find module 'pg'
at Function.Module._resolveFilename (module.js:336:15)
at Function.Module._load (module.js:278:25)
at Module.require (module.js:365:17)
at require (module.js:384:17)
at Object.<anonymous> (c:\Users\User\Documents\restful_koa\node_modul
es\koa-pg\index.js:12:27)
at Module._compile (module.js:460:26)
at Object.Module._extensions..js (module.js:478:10)
at Module.load (module.js:355:32)
at Function.Module._load (module.js:310:12)
at Module.require (module.js:365:17)
This is only a personal project but I'd love to understand where i'm going wrong.
Cheers

Answer 1

As mentioned in the comments:
You need to install the pg module via npm install pg or npm install pg --save if you want to save it to package.json.
The reason you need to do this is koa-pg has co-pg as a dependency so when you install the former the latter is also installed. But pg is not a dependency of co-pg and that is why you have to install it separately.