07 Data Persistence.md

Data Persistence

Data from other APIs / Screen scraping read only

Need to add value to this

Demonstrate CRUD

So need to store data

Script restart needed if code changes

Filesystem

Relational database

Document database

Graph database

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)
})

Document Databases

Good for modelling relationships

Relational Database

Familiar data storage

Supports complex queries

Difficult to scale

Data needs normalising

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)
})

Choosing a Database

Factors:

• Type of data to be stored
• How this will be retrieved
• Complexity

Online Hosting

• Relational MySQL freemysqlhosting.net
• Document MongoDB mlab.com
• Graph Neo4J graphenedb.com