3.4.4: PostgreSQL Express App

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Introduction
For Express we'll use a pg class other than Client. Unlike Node CLI programs that run and exit immediately, Express apps run and listen for requests until stopped. We need a way to manage the database connections that Express makes and end those connections appropriately. pg's Pool class does this automatically, and enables us to accept multiple requests simultaneously. The word pool refers to an available "pool" of connections. We can think of it as a managed array of connection metadata.
Setup
Remember to install pg.
npm install pg
Sample Code
index.js
import express from 'express';
import pg from 'pg';
​
// Initialise DB connection
const { Pool } = pg;
const pgConnectionConfigs = {
  user: '<MY_UNIX_USERNAME>',
  host: 'localhost',
  database: '<MY_UNIX_USERNAME>',
  port: 5432, // Postgres server always runs on this port by default
};
const pool = new Pool(pgConnectionConfigs);
​
const app = express();
​
app.get('/', (request, response) => {
  console.log('request came in');
​
  const whenDoneWithQuery = (error, result) => {
    if (error) {
      console.log('Error executing query', error.stack);
      response.status(503).send(result.rows);
      return;
    }
    console.log(result.rows[0].name);
    response.send(result.rows);
  };
​
  // Query using pg.Pool instead of pg.Client
  pool.query('SELECT * from cats', whenDoneWithQuery);
});
​
app.listen(3004);
Note: There is no need to run pool.end like how we ran client.end with the pg Client class in our Node CLI apps. This is because in server applications we expect the DB connection to persist beyond individual requests.

3.4.3: Nested SQL Queries

3.4.5: Forms for One-to-Many Relationships

Last modified 3mo ago

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Outline

Introduction

Setup

Sample Code