Lecture 3 – Data Storage with
XML+AJAX and MySQL+socket.io
Written by Matthew Shelley for
Professor Wei Shi
Data Storage
• It is often necessary to store game information,
which may or may not change
• In a single-player game, one file is often sufficient
▫ For instance, we might read settings from an XML file
• For an online social game, however, each user may
have their own information, which could be shared
▫ A database such as MySQL can fulfill this need
XML
• XML serves the purposes of describing data
▫ Typically in a hierarchical fashion
• While XML and HTML are structurally very similar,
XML does not do anything with the data it describes
• A basic tag / element:
▫ <tagname attr1=“value1” ... />
• A more complicated tag / element:
▫ <tagname attr1=“value1” ...>...</tagname>
XML
• All XML files should begin with
▫ <?xml version="1.0" encoding="ISO-8859-1"?>
• Comments are written just like in HTML
▫ <!-- COMMENT -->
• Complex data using < and & should be wrapped
with <![CDATA[ and ]]>, e.g.
▫ <![CDATA[<notatag>&&&&</notatag>]]>
XML Example – Multiple Choice Quiz
<?xml version="1.0" encoding="ISO-8859-1"?>
<quiz>
<question q=“Is true false?” correctvalue=“2”>
<answer value=“1”>True</answer>
<answer value=“2”>False</answer>
</question>
<question …>
…
</question>
...
</quiz>
Parsing XML with jQuery
• With an XML file written, we need to be able to
read the data within and then use it
• To do so, we first load the file with AJAX and
then parse it with jQuery similar to HTML
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$.ajax(…)
$(xml).find(‘tag’)
$(xml).children(‘tag’)
$(xml).attr(‘attribute’)
$(xml).text()
AJAX
• “Asynchronous JavaScript and XML” is used to
communicate between the client and the server in
the background, similar to WebSockets
• Data is sent through either GET or POST methods
▫ GET: data is visible in the URL
▫ POST: data is not visible in the URL
▫ Refer to “type” in the upcoming example
• Essentially, AJAX requests a URL, possibly with
data sent along, and returns the server’s response
AJAX + XML Example
• The example provided reads in an XML file
containing three users, and then displays the
results to a table on the web page
• Please refer to
▫ ajax_example.htm
▫ ajax_example.xml
▫ js/ajax_example.js
Useful Links
• XML Introduction
▫ http://www.w3schools.com/xml/xml_whatis.asp
• CDATA
▫ http://www.w3.org/TR/REC-xml/#syntax
• AJAX via jQuery
▫ http://api.jquery.com/jQuery.ajax/
XAMPP
• XAMPP allows you to treat your computer like a web
server, which is helpful for when you want to develop
outside of a live website
• Installing XAMPP gains access to:
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Apache
MySQL
PHP
phpMyAdmin
And a few others...
• Be sure to turn on Apache when you use phpmyAdmin
Download and Install XAMPP
• To download XAMPP, select your version from:
▫ http://www.apachefriends.org/en/xampp.html
• Launch the installer file
▫ It may be necessary to install XAMPP through
“Run as Administrator” on Windows
▫ Unless you know what to exclude, get everything
• Installation will take 15 – 20 minutes
What is a database?
• A database is a collection of tables, where a table
is a collection of entries (rows) with associated
data (columns)
• We perform queries on these tables
▫
▫
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Select
Insert
Update
Delete
Example Tables: ‘users’ + ‘friends’
user_id
username
password
email
1
User_1
Pass_1
e1@host.com
2
User_2
Pass_2
e2@host.com
3
User_3
Pass_3
e3@host.com
user_id
friend_id
1
2
1
3
2
3
What Are Queries?
• Queries describe ‘what we want to find’ or ‘what we
want to happen’ rather than ‘how we will find it’ or
‘how we will make it happen’
• For example, “SELECT userid FROM users”
selects all user ids from the user tables
▫ But, we are not specifying how this operation occurs!
▫ In fact, queries even tend to optimize themselves
• These queries are performed on the server-side
using languages such as PHP or extensions like
node-mysql (as will be our case)
MySQL SELECT – Example 1
• SELECT * FROM users
▫ Returns all rows from ‘users’ with all columns
user_id
username
password
email
1
User_1
Pass_1
e1@host.com
2
User_2
Pass_2
e2@host.com
3
User_3
Pass_3
e3@host.com
MySQL SELECT – Example 2
• SELECT username FROM users
▫ Returns all usernames
username
User_1
User_2
User_3
MySQL SELECT – Example 3
• SELECT userid, username FROM users ORDER
BY userid DESC LIMIT 1
▫ Retrieves the newest user’s userid and username
user_id
username
3
User_3
MySQL SELECT – Example 4
• SELECT * FROM users WHERE (email =
‘em1@host.com’ AND password = ‘password1’)
LIMIT 1
▫ Such a query would be useful for verifying that the
user has provided the correct login information
 Of course, the password should be encrypted
▫ Since user input is often inserted into queries, it is
important to sanitize this input to avoid harmful
“SQL injection”
MySQL INSERT - Examples
• INSERT INTO users (username, password,
email) VALUES (‘User 1’, ‘password1’,
‘email1@host.com’)
• INSERT INTO users SET
username = ‘User 1’,
password = ‘password1’,
email = ‘email1@host.com’
MySQL UPDATE - Example
• UPDATE users SET
username = ‘some_user’,
password = ‘some_password’
WHERE
userid = 2
LIMIT 1
MySQL DELETE - Examples
• DELETE FROM users
WHERE
userid = ‘1’
LIMIT 1
• DELETE FROM some_table ORDER BY
datetime_of_access DESC LIMIT 1
Useful Links
• Select
▫ http://dev.mysql.com/doc/refman/5.5/en/select.html
• Insert
▫ http://dev.mysql.com/doc/refman/5.5/en/insert.html
• Update
▫ http://dev.mysql.com/doc/refman/5.5/en/update.ht
ml
• Delete
▫ http://dev.mysql.com/doc/refman/5.5/en/delete.html
phpMyAdmin
• phpMyAdmin manages MySQL databases and
users, which are assigned privileges
• To access phpMyAdmin:
▫ Start Apache via XAMPP
▫ Start MySQL
▫ Click ‘Admin’ for MySQL to open phpMyAdmin
Create Database
• With phpMyAdmin open, click the “Databases”
tag atop the page
• Name your database and then press “Create”
Create a User
• From the database section, go to “Privileges”
▫ You can see users assigned to this database
▫ You can modify privileges of such users
▫ You can also create a new user
Create a User
Create a Table
• Click the “Create Table” button on the left menu
• Enter the table name and number of columns
• A few notes…
▫ “varchar 255” is a string of length 255
▫ The primary key uniquely identifies a row
▫ auto_increment (A_I) can be given to only one
column, providing it is a key
Create a Table
Modify a Table
• To modify a table go to its ‘structure’ tab
▫ Each column can be modified or removed entirely
▫ You can also add new columns
Additional Table Operations
• From the “database” structure, you can…
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Browse – view rows in a table
Structure – view table structure
Search – perform a query on a table
Insert – add rows to a table
Empty – delete all rows in a table
Drop – delete the entire table
Using node-mysql
• To install node-mysql via command prompt:
▫ npm install mysql@2.0.0-alpha5
• Load the module in code with
▫ var mysql = require(‘mysql’);
• Refer to server-mysql.js and run it via node.js
Using Socket.io + MySQL
• Socket.io is an event-driven API that greatly
simplifies sending and receiving messages
• socket.on(“eventname”, function(data) {…})
▫ Add event listener to any arbitrary event in order
to receive data, e.g. an associative array
• socket.emit(“eventname”, data)
▫ Send along data for an arbitrary event
Useful Links
• mysql-node
▫ https://npmjs.org/package/mysql
• Socket.io
▫ http://socket.io/
• Advanced HTML5 JavaScript: Down 'n Dirty
▫ http://youtu.be/Pm6Ch4qoNe8?t=26m
PHP
• There are many server-side languages, though
PHP is a common one
• If you are using AJAX, you will most likely end
up using PHP for your server-side scripts, as it is
available with most web hosts
• PHP is outside of the scope of this lecture, but
here are a few examples...
Common MySQL Functions in PHP
• These PHP functions are used with MySQL:
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mysql_connect()
mysql_select_db()
mysql_query()
mysql_fetch_assoc()
mysql_error()