Re: Classes - Dumb question
- From: ZeldorBlat <zeldorblat@xxxxxxxxx>
- Date: Thu, 11 Oct 2007 08:41:09 -0700
On Oct 11, 8:57 am, japr...@xxxxxxxxxx (Jason Pruim) wrote:
On Oct 11, 2007, at 8:36 AM, Jay Blanchard wrote:
[snip]
okay, this is really (!) embarassing, but I have to ask:
Why would I want to use classes in PHP?
I have been using PHP for years now and writing the "normal"
functions all
the time. I have never even bothered working with classes, but now
I would
love to know what makes the classes so special...
Please go easy on me ;o) Just trying to make another step :o)
[/snip]
Do not be embarrassed, this is a very good question.
First of all what you call "normal" is procedural or functional
programming. There is nothing wrong with doing things this way and
may be especially quick and efficient when doing basic web sites
and applications. Document well and you will have no problem
maintaining your code.
OOP (object oriented programming) is especially useful when the
application you have created needs to scale. A quick example; you
have sold your products to the consumer market for a long time but
now the commercial market has become interested. Commercial
customers are different than non-commercial customers, different
data, different credit requirements, different shipping, etc. but
they still have a lot in common, If you had a class Customer you
could extended that class to include commercial customers and only
have to code for the unique qualities of that kind of customer.
Then if another type of customer crops up, say a military contract,
you could extend again;
class Customer {
....
}
class CommercialCustomer extends Customer {
/*
*only code unique to commercial customers
* inherits from Customer other variables
* and functions that are common
*/
}
class MilitaryCustomer extends Customer {
/*
*only code unique to military customers
* inherits from Customer other variables
* and functions that are common
*/
}
http://www.sitepoint.com/article/object-oriented-php
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Not trying to hijack the thread... Hopefully this is related enough,
if not I apologize. Would a good use of a class be to write a generic
database connection script? and then feed in the different variables,
such as customer login, database, stuff like that?
something like class DBConnect {
// Connect to database
mysql_connect($server, $login, $password, $database);
}
or no?
--
Kinda sorta. The idea with classes is to expose an interface rather
than an implementation. That enables you to change things inside the
class without having to change how how you use the class.
Consider the following interface:
interface Database {
public function __construct($server, $username, $password,
$database);
public function query($sql);
}
Suppose you're using a MySQL database. Then you might have a MySQL
class that looks something like this (this is a simplified example):
class MySQL implements Database {
private $conn;
public function __construct($server, $username, $password,
$database) {
$this->conn = mysql_connect($server, $username, $password,
$database);
}
public function query($sql) {
return mysql_query($sql, $this->conn);
}
}
So, in your application, you would use this class like this:
$db = new MySQL('foo', 'bar', 'baz', 'xyzzy');
$sql = 'select * from sometable';
$rs = $db->query($sql);
Now let's say you change over to Postgres for your database. Now you
create a class like this:
class Postgres implements Database {
private $conn;
public function __construct($server, $username, $password,
$database) {
$conn_string = "host=$server port=5432 dbname=$database user=
$username password=$password";
$this->conn = pg_connect($conn_string);
}
public function query($sql) {
return pg_query($this->conn, $sql);
}
}
Now your code looks like this:
$db = new Postgres('foo', 'bar', 'baz', 'xyzzy');
$sql = 'select * from sometable';
$rs = $db->query($sql);
Notice how the details of connecting and running a query (like the
functions used, for instance) are encapsulated inside the class. When
I go to actually use the database all I need to know is that there is
some method called "query" which, given some SQL, runs the query and
returns a result. I know that both the MySQL class and the Postgres
class have a method called query() because they both implement the
"Database" interface. I don't care about the specifics of what
happens inside the class -- but I know I can treat both objects as
though they are the same (that's called "polymorphism") because they
are both "Databases."
Does that make sense?
.
- References:
- RE: [PHP] Classes - Dumb question
- From: "Jay Blanchard"
- Re: [PHP] Classes - Dumb question
- From: Jason Pruim
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