09 Data Persistence.md

Data Persistence

1 Filesystem

Stores text in file against key

Formatted as JSON data

Easy to store and retrieve by key

Simple to implement

Difficult to query

const storage = require('node-persist')
storage.initSync()

exports.addBook = function(isbn, callback) {
  const data = {
    title: 'The Hobbit',
    authors: 'J.R.R. Tolkien',
    description: 'Hobbit finds ring...'
  }
  storage.setItemSync(isbn, data)
}

2 Document Database

Stores JavaScript objects

Can be queried using JavaScript

2.1 Installing MongoDB

There are several ways to access a MongoDB database. You can make use of a cloud provider such as mLab or you can install the database locally on your development machine.

2.1.1 Installing on Ubuntu

2.1.2 Installing on MacOS

The best way to install it on a Mac is to use the Homebrew package manager. The installation instructions can be found in the introductory chapter of this book. To install MongoDB

$ brew install mongodb

You need to create a data directory and change its permissions before starting the database server.

$ mkdir -p /data/db
$ sudo chown -R `id -un` /data/db
$ mongod

Mongoose Example.

Start by defining a schema file:

const mongoose = require('mongoose')
mongoose.Promise = global.Promise
const Schema = mongoose.Schema

const bookSchema = new Schema({
  title: String,
  authors: String,
  description: String
})
const Book = mongoose.model('Book', bookSchema)
module.exports = Book

Storing a document.

const book = new Book({
  title: data.title,
  authors: data.authors,
  description: data.description
})

book.save( function(err, book) {
if (err) {
    callback( Error(`database error: ${err}`) )
  }
  return callback(null, book)
})

3 Relational Database

const mysql = require('mysql')
const request = require('request')

const connection = mysql.createConnection({ host: 'xxx', port: '3306', user: 'xxx', password: 'xxx', database: 'xxx' })

const sql = 'INSERT INTO books (id, title, authors, description) VALUES (NULL, "The Hobbit, "J.R.R. Tolkien", "Ring found")'

connection.query(sql, (err, rows) => {
  if (err) callback( Error(`database error: ${err}`) )
  return callback(null, rows)
})