Databases/JQuery AUGUST 1, 2018

Transcription

1 Databases/JQuery AUGUST 1, 2018

2 Databases What is a Database? A table Durable place for storing things Place to easily lookup and update information

3 Databases: The M in MVC What is a Database? Your Model Your View and Controller fetch data from it

4 Databases Why databases? Tabular format is easy to access Conventions in language and access model simplify things

5 Databases Types SQL NoSQL

6 Databases SQL Rigid syntax Represent things as tables Use the Sequential Query Language E.g select firstname, lastname FROM users WHERE lastname = `banda` Example: MySQL, PostgreSQL

7 Databases SQL = Sequential Query Language SELECT title FROM book WHERE author = `Darren Jones`; Book Table ISBN title author format price JavaScript: Novice to Ninja Darren Jones ebook Jump Start Git Shaumik Daityari ebook 29.00

8 Databases NoSQL Document { ISBN: , title: "JavaScript: Novice to Ninja", author: "Darren Jones", format: "ebook", price: } NoSQL sticks the native language syntax Examples: Mongodb, Couchdb

9 Databases Databases usually run in separate process so any framework can usually us any database Framework e.g Node.JS View Controller Database e.g MySQL MongoDB

10 NoSQL vs SQL

11 NoSQL vs SQL For most small applications no big difference Generally, the answer depends on how strictly a tabular format benefits your App and your knowledge of SQL

12 NoSQL vs SQL NoSQL has some advantages especially for beginners SQL can be annoying SQL can be unsafe SQL injection attacks SQL bugs can be hard to detect

13 SQL Injection Attacks

14 SQL Injection Attacks: Example Users Table Name Phone Password April Sandhya 4567 password Dalitso 8920 hello Suppose we had a website to look up phone numbers

15 SQL Injection Attacks: Example Hacking a phone directory Enter your name: SELECT phone FROM users WHERE name = Dalitso; Dalitso SQL Database 8920

16 SQL Injection Attacks: Example Hacking a phone directory: Bad code var name = $('#input').text() // name = "Dalitso" var query = "SELECT phone FROM users WHERE name =" + name + ";" var phone = sendquerytodatabase(query) // send query to database

17 SQL Injection Attacks: Example Hacking a phone directory Enter your name: Dalitso; SELECT name, password FROM users;

18 SQL Injection Attacks: Example Hacking a phone directory SELECT phone FROM users WHERE name = Dalitso; SELECT name, password FROM users; Enter your name: SQL Database All usernames and passwords

19 SQL Injection Attacks: Example Hacking a phone directory: Possible Fix var name = $('#input').text() // name = "Dalitso" var query = connection.query("select phone FROM users WHERE name =?, name) var phone = sendquerytodatabase(query) // send query to database

20 SQL Injection Attacks: Example Fixes Prevent the user from inputting special symbols Sanitize all input Use library to construct queries instead of +

21 NoSQL avoids bad injection attacks NoSQL uses functions instead of passing SQL Enter your name: Dalitso find({name: Dalitso }, function(response){ sendtouser(response); }) NoSQL Database

22 Some Problems with NoSQL Not standardized query language NoSQLs have different APIs Big systems can be difficult in the document model Some NoSQLs have poor performance and consistency

23 Some Problems with NoSQL Not standardized query language Example: MongoDB in NodeJS behavior different from Python Django NodeJS MongoDB callback hell

24 MongoDB in NodeJS var MongoClient = require('mongodb').mongoclient; var url = "mongodb://localhost:27017/mydb"; var database; function connectcallback(err, db){ console.log("database created!"); database = db } MongoClient.connect(url, connectcallback)

25 MongoDB in NodeJS In nodejs, callbacks are executed asynchronously Asynchronously means at any time Programmer has to be careful Callbacks can lead to verbosity problem know as callback hell Try to break code into pieces to avoid callback hell

26 MongoDB in NodeJS: Asynchrony var database; function connectcallback(err, db){ console.log("database created!"); database = db } MongoClient.connect(url, connectcallback) console.log(database) // undefined!

27 MongoDB in NodeJS: Callback hell var MongoClient = require('mongodb').mongoclient; var url = "mongodb://localhost:27017/mydb"; var database; MongoClient.connect(url, function(err, db){ console.log("database created!"); database = db; })

28 MongoDB in NodeJS: Callback hell var MongoClient = require('mongodb').mongoclient; var url = "mongodb://localhost:27017/mydb"; var database; MongoClient.connect(url, function(err, db){ console.log("database created!"); database = db database.collection("users").findone({name: "Dalitso"}, function(err, result) { console.log(result.phone); }); })

29 MongoDB in NodeJS: Fixed Code var MongoClient = require('mongodb').mongoclient; var url = "mongodb://localhost:27017/mydb"; var database; function connectcallback(err, db){ console.log("database created!"); database = db database.collection("users").findone({name: "Dalitso"}, findphone) } function findphone(err, result) { console.log(result.phone); } MongoClient.connect(url, connectcallback)

30 JQuery

31 JQuery Large client JavaScript library Easy way to make AJAX calls What is AJAX? GET, POST requests. HTTP Verbs Uses callbacks like MongoDB

32 Jquery Example: Site to show names <!DOCTYPE html> <html> <head> <script src=" </head> <body> <button id = "btn">click me</button> <p id="names">names<p> </body> </html>

33 JQuery Example: Site to show names The jquery library is accessed using $ $ is not a special syntax but just the name for variable Calling $ with a string, runs the selector function E.g $( #button ) The selector function is used to access html elements in JavaScript

34 JQuery Example: Site to show names function handlenames(names_data){ var names = $("#names"); names.text(names_data); } function getnames(){ } $.get( handlenames); var btn = $("#btn"); btn.click(getnames);

35 <!DOCTYPE html> <html> <head> <script src=" </head> <body> <button id = "btn">click me</button> <p id="names">names<p> <script type="text/javascript"> function handlenames(names_data){ var names = $("#names"); names.text(names_data); } function getnames(){ $.get(" handlenames); } var btn = $("#btn"); btn.click(getnames); </script> </body> </html>

36 Exercise: Try to replicate what we just did. The link to the names file: mes.txt