Web-Based Database Programming with PHP. Dept. of Computing Science, University of Aberdeen2 In this...

Web-Based Database Programming with PHP

Dept. of Computing Science, University of Aberdeen 2

In this lecture you will learn

• PHP Basics• PHP functions

– To check and filter user inputs (security)– To connect to database– To select database– To query database– To work with the results

• BLOB types in MySQL• Displaying BLOBS• Debugging tips

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PHP

• General purpose scripting language– Can be used to achieve functionality

similar to Java or C– Similar to C in syntax– Server side scripting language

• Code is run on the server and the resulting html page is shown in the browser

• This means, users cannot view the php source code

• Libraries used for accessing RDBMS– Several vendor specific libraries available

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PHP Variables

• Starts with $ symbol followed by name• Name contains letters, numbers and underscore

– Cannot start with a number– No special characters other than underscore (_)– Case sensitive

• E.g. $query and $result• Variables are not typed

– Type of value assigned determines a variable’s type– Within a program, same variable can be assigned to

values of different data types!!!

• $this is a special variable that cannot be assigned– Refers to the object of a class, similar to Java

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PHP Arrays

• Two kind of arrays• Numeric Arrays

– Similar to Java arrays– Objects/values are accessed by a numerical index– E.g. $color = array(‘Red’,‘Blue’,’Green’);– $redcolor = $color[0];

• Associative Arrays– Objects/values are stored as pairs of (key=>value)

elements– Objects/values are accessed by specifying the key– Similar to Java Maps– E.g. $lecturer = array(‘CS2008’=>’Yaji’,

‘CS2007’=>’Ehud’);– $cs2008Lecturer = $lecturer[‘CS2008’];

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Predefined Variables

• PHP provides several predefined variables to be used in scripts– Depends upon the server setup

• Variables from HTML forms are available in an associative array $_POST

• E.g. If $_POST = array(‘name’=>’John’, ‘age’=>44,’email’=>’john@somewhere.com’)

Then $age = $_POST[‘age’]; and $email = $_POST[‘email’];

• In the practical, you will learn using variables from HTML forms in your PHP scripts.

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PHP Strings

• Several Types of strings• We use two string types• Single quoted

– Use them for storing literal strings– E.g. ‘Yaji teaches CS2008’

• Double quoted– Use them with embedded variables– E.g. “$cs2008Lecturer teaches CS2008”

Where $cs2008Lecturer=‘Yaji’• Several string manipulation functions

– Useful for checking and filtering user inputs

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Check and filter data coming from the user

• User inputs may contain character(s) that might be harmful to the server or database– Sometimes they may contain entire

scripts that may cause problems to the server or database

– Never trust user inputs!!!• PHP provides a number of functions

to remove undesirable characters from user inputs.

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While storing user input into MySQL

• Certain characters have special meaning for MySQL

• Example special characters– Single quote (’)– Double quote (“)– Backslash (\)– NULL

• You need to use the escape character,\ to mark them– E.g., \’ means ’– \” means ”

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addslashes() and stripslashes()

• addslashes(X) adds backslash characters to X– E.g addslashes(‘Yaji’s laptop’) will return ‘Yaji\’s laptop’

• stripslashes(X) removes backslash characters from X

• PHP offers another way of adding and removing backslashes: switch on the – magic_quotes_gpc (for incoming data from browser) and – magic_quotes_runtime (for data going to database)

directives in your php.ini file

• You can use trim() function to remove extra white spaces

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escapeshellcmd(), strip_tags() and

htmlspecialchars()• escapeshellcmd(X) should be used

before passing X to system() and exec() which run shell commands

• Before you ‘echo’ back user input to the browser use– strip_tags(X) – strips out HTML and PHP

tags from X– htmlspecialchars(X) – converts special

characters to HTML equivalents• E.g., < is converted to &lt

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To connect to MySQL• Syntaxresource mysql_connect ( [string server [, string username [, string password [, bool

new_link [, int client_flags]]]]])

• Server = name of the server or IP address• By default mysql_connect returns an existing

open link– Specify new_link if you want a new link

• Client_flags– MYSQL_CLIENT_COMPRESS

• Use compression protocol– MYSQL_CLIENT_IGNORE_SPACE

• Allow space after function names– MYSQL_CLIENT_INTERACTIVE

• Allow interactive_timeout seconds (instead of wait_timeout) of inactivity before closing the connection.

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include() or require()• Your PHP script is never seen by your browser

– Password used in mysql_connect cannot be seen by users

• You may still like to create dbsetup.php to define global variables– $username– $server– $password

• And include($path.‘dbsetup.php’) or require($path.‘dbsetup.php’) in your .php file

• Include and require are same– They differ only when they fail

• Include produces a warning• Require results in a Fatal Error

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mysql_error() & mysql_errno()

• After calling any mysql functions (mysql_xxx)

• You can call mysql_error($link) and mysql_errno($link)

• $link is the active connection to MySQL

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Selecting a database

• After making the connection to MySQL server

• You need to select the database you want to work with using– mysql_select_db()

• Syntaxbool mysql_select_db ( string

database_name [, resource link_identifier])• Link_identifier is the active connection to

MySQL

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Querying

• Define the query string such as$Query = ‘select * from staff’;• Then use mysql_query() to run the

query• Syntaxresource mysql_query ( string query [,

resource link_identifier])• E.g$result = mysql_query($Query,$link);

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Functions for Results Object

• PHP offers many functions for working with the results object– array mysql_fetch_row ( resource result) –

fetches a row as an array– object mysql_fetch_field ( resource result [, int

field_offset]) – fetches a field as an object– array mysql_fetch_assoc ( resource result) –

fetches a row as an associative array• You can access fields in the row with the field names• E.g. $row[‘lname’]

– int mysql_num_fields ( resource result)– int mysql_num_rows ( resource result)

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Closing the connection

• When the script ends executing connection is closed or

• Use– mysql_free_result($result);– Mysql_close($link);

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Storing Multimedia - BLOBS

• How should large text files, images or sound files be stored in DBMSs ?

• Solution 1: Store a reference to an external file:

• Solution 2: Store as a BLOB:

PictureNo c:nimagesnpicture.jpg

PictureNo BLOB

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Storing BLOBS in MySQL

• There are four BLOB data types in MySQL each with different maximum capacity– TINYBLOB– BLOB– MEDIUMBLOB– LONGBLOB

• BLOB columns are treated as binary strings

• For exampleCREATE img (id int(5) PRIMARY KEY, pic BLOB);

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Displaying BLOB Images

• Usually, images are streamed to the client from a file on the server:

<IMG SRC="images/the_image.jpg">• If the image is stored in a database, we need the

help of a script to stream the blob to the client from the database:

// $id = select_the_property_somehow();printf(“<img src = getImg.php?id=%b>”,$id);

• You will use getImg.php in Practical 8...• You are NOT required to learn stream

programming!!

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Debugging Tips

• Because PHP is not strongly-typed, and is interpreted at run-time on the server, debugging a faulty script can be very tricky!!!

• Use echo() often to print to the client!!• Check code for ";" at end of every statement!!• Check code for matching pairs of quotes!!• Avoid variable names like "system" !!• Ask yourself: is it a DB problem or a script

problem??• Check your SQL statement with MS-Access or

MySQL client!!• Divide-and-conquer: comment-out doubtful code!!