Pdf form save software control dll winforms web page html web forms 05-welling-php-mysql-web30-part77

267

How Web Database Architectures Work

<br />

</form>

</body>

</html>

This HTML form is reasonably straightforward.The output of this HTML is shown in

Figure 11.1.

Listing 11.1

Continued

Figure 11.1 The search form is quite general, so you can search for a book

on its title, author, or ISBN.

The script that will be called when the Search button is clicked is

results.php

.It is

listed in full in Listing 11.2.Through the course of this chapter,we will discuss what this

script does and how it works.

Listing 11.2 results.php—This Script Retrieves Search Results from the MySQL

Database and Formats Them for Display

<html>

<head>

<title>Book-O-Rama Search Results</title>

</head>

<body>

<h1>Book-O-Rama Search Results</h1>

<?php

// create short variable names

$searchtype=$_POST[‘searchtype’];

$searchterm=$_POST[‘searchterm’];

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268

Chapter 11 Accessing Your MySQL Database from the Web with PHP

$searchterm= trim($searchterm);

if (!$searchtype || !$searchterm)

{

echo ‘You have not entered search details. Please go back and try again.’;

exit;

}

if (!get_magic_quotes_gpc())

{

$searchtype = addslashes($searchtype);

$searchterm = addslashes($searchterm);

}

@ $db = new mysqli(‘localhost’, ‘bookorama’, ‘bookorama123’, ‘books’);

if (mysqli_connect_errno())

{

echo ‘Error: Could not connect to database. Please try again later.’;

exit;

}

$query = “select * from books where “.$searchtype.” like ‘%”.$searchterm.”%’”;

$result = $db->query($query);

$num_results = $result->num_rows;

echo ‘<p>Number of books found: ‘.$num_results.’</p>’;

for ($i=0; $i <$num_results; $i++)

{

$row = $result->fetch_assoc();

echo ‘<p><strong>’.($i+1).’. Title: ‘;

echo htmlspecialchars(stripslashes($row[‘title’]));

echo ‘</strong><br />Author: ‘;

echo stripslashes($row[‘author’]);

echo ‘<br />ISBN: ‘;

echo stripslashes($row[‘isbn’]);

echo ‘<br />Price: ‘;

echo stripslashes($row[‘price’]);

echo ‘</p>’;

}

Listing 11.2 Continued

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269

Querying a Database from the Web

$result->free();

$db->close();

</body>

</html>

Note that this script allows you to enter the MySQL wildcard characters

and _

(underscore).This capability can actually be useful for the user.You can escape these

characters if it will cause a problem for your application.

Figure 11.2 illustrates the results of using this script to perform a search.

Listing 11.2 Continued

Figure 11.2 The results of searching the database for books about Java are

presented in a web page using the

results.php

script.

Querying a Database from the Web

In any script used to access a database from the Web,you follow some basic steps:

1. Check and filter data coming from the user.

2. Set up a connection to the appropriate database.

3. Query the database.

4. Retrieve the results.

5. Present the results back to the user.

These are the steps we followed in the script

results.php

,so now let’s go through each

of them in turn.

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270

Chapter 11 Accessing Your MySQL Database from the Web with PHP

Checking and Filtering Input Data

You begin the script by stripping any whitespace that the user might have inadvertently

entered at the beginning or end of his search term.You do this by applying the function

trim()

$searchterm

$searchterm=trim($searchterm);

The next step is to verify that the user has entered a search term and search type. Note

that you check whether he entered a search term after trimming whitespace from the

ends of

$searchterm

.If you arrange these lines in the opposite order, you could

encounter situations in which a user’s search term is not empty and therefore does not

create an error message;instead,it is all whitespace,so it is deleted by

trim()

if (!$searchtype || !$searchterm)

{

echo ‘You have not entered search details. Please go back and try again.’;

exit;

}

You check the

$searchtype

variable even though in this case it’s coming from an

HTML

SELECT

.You might ask why you should bother checking data that has to be filled

in.It’s important to remember that there might be more than one interface to your data-

base.For example,Amazon has many affiliates who use its search interface.Also,it’s sensi-

ble to screen data in case of any security problems that can arise because of users coming

from different points of entry.

Also,when you plan to use any data input by a user,you need to filter it appropriate-

ly for any control characters.As you might remember,in Chapter 4,“String

Manipulation and Regular Expressions,”we described the functions

addslashes()

stripslashes()

,and

get_magic_quotes_gpc()

.You need to escape data when submit-

ting any user input to a database such as MySQL.

In this case,you check the value of the

get_magic_quotes_gpc()

function.It tells

you whether quoting is being done automatically.If it is not,you use

addslashes()

escape the data:

if (!get_magic_quotes_gpc())

{

$searchtype = addslashes($searchtype);

$searchterm = addslashes($searchterm);

}

You also use

stripslashes()

on the data coming back from the database. If the magic

quotes feature is turned on,the data will have slashes in it when it comes back from the

database,so you need to take them out.

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271

Setting Up a Connection

Here, you use the function

htmlspecialchars()

to encode characters that have spe-

cial meanings in HTML.The current test data does not include any ampersands (

),less

than (

),greater than (

),or double quotation mark (

“

) symbols,but many fine book

titles contain an ampersand.By using this function,you can eliminate future errors.

Setting Up a Connection

PHP5 has a new library for connecting to MySQL.This library is called mysqli (the i

stands for improved).The mysqli library is suitable for use with MySQL version 4 and

later.At version 4,a new connection protocol that is much faster was added to MySQL,

and mysqli allows you to take advantage of it.The mysqli library allows you to use either

an object-oriented or procedural syntax.

You use the following line in the script to connect to the MySQL server:

@ $db = new mysqli(‘localhost’, ‘bookorama’, ‘bookorama123’, ‘books’);

This line instantiates the

mysqli

class and creates a connection to host

‘localhost’

with username

‘bookorama’

,and password

‘bookorama123’

.The connection is set up

to use the database called books.

Using this object-oriented approach,you can now invoke methods on this object to

access the database.If you prefer a procedural approach,mysqli allows for this,too.To

connect in a procedural fashion,you would use

@ $db = mysqli_connect(‘localhost’, ‘bookorama’, ‘bookorama123’, ‘books’);

This function returns a resource rather than an object.This resource represents the con-

nection to the database, and if you are using the procedural approach, you will need to

pass this resource in to all the other mysqli functions.This is very similar to the way the

file-handling functions,such as

fopen()

,work.

Most of the mysqli functions have an object-oriented interface and a procedural

interface.Generally,the differences are that the procedural version function names start

with

mysqli_

and require you to pass in the resource handle you obtained from

mysqli_connect()

.Database connections are an exception to this rule because they can

be made by the mysqli object’s constructor.

The result of your attempt at connection is worth checking because none of the rest of

code will work without a valid database connection.You do this using the following code:

if (mysqli_connect_errno())

{

echo ‘Error: Could not connect to database. Please try again later.’;

exit;

}

(This code is the same for the object-oriented and procedural versions.) The

mysqli_connect_errno()

function returns an error number on error,or zero on success.

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272

Chapter 11 Accessing Your MySQL Database from the Web with PHP

Note that when you connect to the database,you begin the line of code with the

error suppression operator,

.This way,you can handle any errors gracefully.(This could

also be done with exceptions,which we have not used in this simple example.)

Bear in mind that there is a limit to the number of MySQL connections that can

exist at the same time.The MySQL parameter

max_connections

determines what this

limit is.The purpose of this parameter and the related Apache parameter

MaxClients

to tell the server to reject new connection requests instead of allowing machine

resources to be completely used up at busy times or when software has crashed.

You can alter both of these parameters from their default values by editing the con-

figuration files.To set

MaxClients

in Apache,edit the

httpd.conf

file on your system.

To set

max_connections

for MySQL, edit the file

my.conf

Choosing a Database to Use

Remember that when you are using MySQL from a command-line interface,you need

to tell it which database you plan to use with a command such as

use books;

You also need to do this when connecting from the Web.The database to use is specified

as a parameter to the

mysqli

constructor or the

mysqli_connect()

function.If you

want to change the default database,you can do so with the

mysqli_select_db()

func-

tion.It can be accessed as either

$db->select_db(dbname)

or as

mysqli_select_db(db_resource, db_name)

Here, you can see the similarity between the functions that we described before:The

procedural version begins with

mysqli_

and requires the extra database handle

parameter.

Querying the Database

To actually perform the query,you can use the

mysqli_query()

function.Before doing

this,however,it’s a good idea to set up the query you want to run:

$query = “select * from books where $searchtype like ‘%$searchterm%’”;

In this case,you search for the user-input value (

$searchterm

) in the field the user spec-

ified (

$searchtype

).Notice the use of

for matching rather than

equal

:it’s usually

a good idea to be more tolerant in a database search.

Tip

Remember that the query you send to MySQL does not need a semicolon at the end of it, unlike a query you

type into the MySQL monitor.

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273

Retrieving the Query Results

You can now run the query:

$result = $db->query($query);

Or,if you wanted to use the procedural interface,you would use

$result = mysqli_query($db, $query);

You pass in the query you want to run and, in the procedural interface,the database link

(again,in this case

$db

The object-oriented version returns a result object;the procedural version returns a

result resource.(This is similar to the way the connection functions work.) Either way,

you store the result in a variable (

$result

) for later use.This function returns

false

failure.

Retrieving the Query Results

Alarge variety of functions is available to break the results out of the result object or

identifier in different ways.The result object or identifier is the key to accessing the rows

returned by the query.

In this example,you counted the number of rows returned and also used the

mysqli_fetch_assoc()

function.

When you use the object-oriented approach,the number of rows returned is stored

in the

num_rows

member of the result object,and you can access it as follows:

$num_results = $result->num_rows;

When you use a procedural approach,the function

mysqli_num_rows()

gives you the

number of rows returned by the query.You should pass it the result identifier,like this:

$num_results = mysqli_num_rows($result);

It’s useful to know this—if you plan to process or display the results,as you now know

how many there are and can loop through them:

for ($i=0; $i <$num_results; $i++)

{

// process results

}

In each iteration of this loop,you call

$result->fetch_assoc()

(or

mysqli_fetch_assoc()

).The loop does not execute if no rows are returned.This is a

function that takes each row from the resultset and returns the row as an array, with each

key an attribute name and each value the corresponding value in the array:

$row = $result->fetch_assoc();

Or you can use a procedural approach:

$row = mysqli_fetch_assoc($result);

274

Chapter 11 Accessing Your MySQL Database from the Web with PHP

Given the array

$row

,you can go through each field and display it appropriately,as

shown in this example:

echo ‘<br />ISBN: ‘;

echo stripslashes($row[‘isbn’]);

As previously mentioned,you call

stripslashes()

to tidy up the value before display-

ing it.

Several variations can be used to get results from a result identifier.Instead of an array

with named keys,you can retrieve the results in an enumerated array with

mysqli_fetch_row()

,as follows:

$row = $result->fetch_row($result);

$row = mysqli_fetch_row($result);

Here, the attribute values are listed in each of the array values

$row[0]

$row[1]

,and so

on.(The

mysqli_fetch_array()

function allows you to fetch a row as either or both

kinds of array.)

You could also fetch a row into an object with the

mysqli_fetch_object()

func-

tion:

$row = $result->fetch_object();

$row = mysqli_fetch_object($result);

You can then access each of the attributes via

$row->title

$row->author

,and so on.

Disconnecting from the Database

You can free up your resultset by calling either

$result->free();

mysqli_free_result($result);

You can then use

$db->close();

mysqli_close($db);

to close a database connection.Using this command isn’t strictly necessary because the

connection will be closed when a script finishes execution anyway.

275

Putting New Information in the Database

Inserting new items into the database is remarkably similar to getting items out of the

database.You follow the same basic steps: make a connection, send a query, and check the

results. In this case,the query you send is an

INSERT

rather than a

SELECT

Although this process is similar,looking at an example can sometimes be useful. In

Figure 11.3,you can see a basic HTML form for putting new books into the database.

Figure 11.3 This interface for putting new books into the database could be

used by Book-O-Rama’s staff.

The HTML for this page is shown in Listing 11.3.

Listing 11.3 newbook.html— HTML for the Book Entry Page

<html>

<head>

<title>Book-O-Rama - New Book Entry</title>

</head>

<body>

<h1>Book-O-Rama - New Book Entry</h1>

<tr>

</tr>

<tr>

<td>Author</td>

</tr>

276

Chapter 11 Accessing Your MySQL Database from the Web with PHP

<tr>

<td>Title</td>

</tr>

<tr>

<td>Price $</td>

</tr>

<tr>

</tr>

</table>

</form>

</body>

</html>

The results of this form are passed along to

insert_book.php

,a script that takes the

details,performs some minor validations,and attempts to write the data into the data-

base.The code for this script is shown in Listing 11.4.

Listing 11.4 insert_book.php— This Script Writes New Books into the Database

<html>

<head>

<title>Book-O-Rama Book Entry Results</title>

</head>

<body>

<h1>Book-O-Rama Book Entry Results</h1>

<?php

// create short variable names

$isbn=$_POST[‘isbn’];

$author=$_POST[‘author’];

$title=$_POST[‘title’];

$price=$_POST[‘price’];

if (!$isbn || !$author || !$title || !$price)

{

echo ‘You have not entered all the required details.<br />’

.’Please go back and try again.’;

exit;

}

if (!get_magic_quotes_gpc())

{

Listing 11.3 Continued

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