PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Querying a Database from the Web
273
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 use
@ $db = mysqli_connect('localhost', 'bookorama', 'bookorama123', 'books');
This function returns a resource rather than an object.This resource represents the connection
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.
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 is
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 configuration
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.