notes.md

Books Refactor

In this lecture, we are going to be refactoring a reading list Express application.

Click here to clone the repo!

Currently, that application's model uses an in-memory array to manage a list of books. As a result, the data will only persist as long as the server is up and running. We will refactor this project using Knex to connect to a PostgreSQL database to manage a persistent set of data.

Setup + File Structure

• Create a database called books
• create src/db folder
• npx knex init
• Configure the knexfile.js (remember to require('path'))

const path = require('path');

module.exports = {
  development: {
    client: 'pg',
    connection: {
      database: 'books',
      user:     'benspector',
      password: 'postgres'
    },
    migrations: {
      directory: path.join(__dirname, 'src', 'db', 'migrations')
    },
    seeds: {
      directory: path.join(__dirname, 'src', 'db', 'seeds')
    }
  }
}

• npx knex migrate:make create_books_table

exports.up = (knex) => {
  return knex.schema.createTable('books', (table) => {
    table.increments('id').primary();
    table.string('title').notNullable();
    table.string('published_year').notNullable();
  });
};

exports.down = (knex) => {
  return knex.schema.dropTable('books');
};

• npx knex migrate:latest
• npx knex seed:make seed_books

exports.seed = async function(knex) {
  // Deletes ALL existing entries
  await knex('books').del()
  await knex('books').insert([
    { title: 'Learn to Git With It',	published_year: 2015 },
    { title: 'HTML for Dummies',	published_year: 2018 },
    { title: 'Advanced JavaScript',	published_year: 2009 },
    { title: 'Starting Express',	published_year: 2010 },
    { title: 'Node for Noobies',	published_year: 2020 }
  ]);
};

• npx knex seed:run

Refactoring the Model + Controllers

• move src/models folder into src/db (update the src/middleware/add-books import)
• Test to make sure everything still works!
• create src/db/models/knex.js file

const env = 'development';
const config = require('../../../knexfile')[env];
const knex = require('knex')(config);

module.exports = knex;

• Update src/models/books/ to use knex
  • We don't need the static #all array anymore!
  • Replace array manipulation logic with knex.raw queries
  • Remember to use try/catch!

Here is an example:

static async list() {
  try {
    const result = await knex.raw(`
      SELECT *
      FROM books;
    `);
    return result.rows;
  } catch (err) {
    console.error(err);
    return null;
  }
}

• Update controller functions to use async and await.
• Instead of using the Book constructor, we'll use a static create method.
• Update src/controllers/books/create to use the Book.create method instead of the constructor.

Celebrate!