What do you mean by MVC ?

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What do you mean by MVC ?..

Answer / abinash grahacharya

MVC stands for Model-View-Controller. It is a type of
architecture for developing software, recently pretty
popular in web applications development. In short, the three
things are pretty simple. Model is what interacts with the
database, it would be the backend class code for an
object-oriented language like PHP, Ruby on Rails, or C++.
View is basically the user interface. Controller is the
logic that operates everything in between.

They are easy to explain, but sometimes the concept is a
little abstract and it’s hard to grasp for someone who
doesn’t know what MVC is to begin with. To be honest, all my
years in web development I never really understood exactly
what MVC is, until recently when I started doing development
in Ruby on Rails. In this article, I hope to explain MVC
architecture development in PHP terms, so the average web
apps programmer may benefit from understanding this powerful
architecture.

MVC and PHP development

The reason I mentioned Ruby on Rails is because you really
have to understand how to develop an application with the
MVC architecture to do anything at all on RoR. (Next time, I
will write another article on RoR — but this time, I’ll talk
about PHP development.)

The Model-View-Controller separation actually makes a lot of
sense, it is actually natural for a developer to divide
his/her code that way when working on a reasonably large
application. Java has classes, JSP and struts; Ruby on Rails
has a built-in MVC structure; but even when PHP doesn’t have
anything like that, it doesn’t mean you can’t do it.

The Model

The MVC structure is meant for reasonably-sized
applications, using object-oriented coding. The Model part,
in a PHP app, would usually be a class (or multiple
classes). Fairly often, the class is a representation of a
table you store in the database — member variables are the
data columns, and member methods are operations that can be
done. As an example, you might have a User class, having
variables such as username, password, email address, and
other things. Some of its methods might be a new user
creation function, a login function, an authentication
function, and a logout function.

Later on, we will see how User objects will be used in the
Controller part of your application. The Model, in essence,
tells you what methods are available — what can you do to
the data in the database. I thought I should just clarify
(if it wasn’t clear already) — this should be all PHP code,
just as what you should do in OO-programming even without
MVC. There should be no HTML or any kinds of outputs
(redirection, etc.) here. If doing an action means that a
redirection is needed or some output is needed, pass it as
an argument or a return value. (It’s fairly basic
programming practices, but you’d be surprised how many web
apps programmers didn’t graduate with a CS degree..)

Here’s an example of the Model part of your code. Of course,
there will be many more classes in a real application. This
is just the code is the simplest form, without a lot of the
details.

class User
{
var $username;
var $password;
var $email;
function User($u, $p, $e) // constructor
{
$this->username = $u;
$this->password = $p;
$this->email = $e;
}
function create()
{
// creates user in the db
}
function login()
{
// checks against db, does login procedures
}
static function authenticate($u, $p)
{
// checks against db
}
function logout()
{
// does logout procedures
}
}

The View

The View, in the simplest words, is the user interface.
However, it doesn’t mean it would be just straight HTML.
Minimal PHP logic will need to be used in your application’s
interface a lot of times. For example, if you were to have
the main logged-in page say, “Hello, [username]!” You would
certainly need some PHP code to handle that, right? That is
all part of the View. Of course, all the CSS, Javascript
would be part of this too.

It is important that whatever PHP code in here is only what
needs to be used to display the interface correctly. No
additional “action” code belongs to the View — that is the
Controller’s job, which we’ll see next.

This was easy to understand, but for clarification’s sake,
let’s see an example anyway. Of course, the following isn’t
even valid XHTML 1.0 (it lacks a DOCTYPE, for instance), but
this is just an example.

<?php
require_once('User.php');
// makes sure user isn't already logged in
if (User::authenticate($_COOKIE['username'],
$_COOKIE['password']))
{
header(”Location:/main.php”);
exit();
}
?>
<html>
<head><title>Please login</title></head>
<body>
<h1>Login</h1>
<?
if ($_GET['error'] == 1)
{
echo ‘Login incorrect. Please try again.<br />’;
}
?>
<form action=”login_action.php” method=”post”>
User: <input type=”text” name=”username” /><br />
Pass: <input type=”password” name=”password” /><br />
<input type=”submit” value=”Login” />
</form>
</body>
</html>

The Controller

Sometimes it is confusing to understand what the Controller
needs to do, if you weren’t working on an actual application
and just reading a book/an article. It would seem like the
Model and the View are all you need. So let’s go back to a
concrete PHP example.

Now imagine you have a login page setup. The login HTML form
has to submit to somewhere, right? (Even if you’re using
AJAX) You don’t submit directly to the Model class file
(say, User.php), because that file only contains the class
code, and no actual procedural code is there, so it won’t do
anything. You certainly don’t submit directly back to the
View file (say, login.php), even if it ends with a .php
extension! Because its job is only to display the interface.

This is what the Controller is. Your form will submit to a
file, say, login_action.php. In this file, you create an
instance of the User class, running whatever initialization
you need, and calling the appropriate methods that need to
be run (login).

Some developers fall into the temptation to display outputs
from the Controller, because it’s convenient. Imagine, if
you had a login form, how easy is it to just print “Login
incorrect” directly from the Controller PHP code? (assuming
you aren’t using AJAX, for this particular example) It is an
option, and I will tell you that many scripts do just that.
However, to truly utilize a MVC structure’s advantage, the
Controller (like the Model) should not display any HTML
outputs, but rather use redirection. You may use
cookies/sessions, database storage, flat file caching, or
query string to the View file to store the states of your
application; and then you should always let the View take
care of displaying outputs, using these stored states.

Now let’s see an example of a Controller code.

<?php
require_once('User.php');
// in reality, a lot more error checking needs to be done.
$currentuser = new User($_POST['username'],
$_POST['password'], ”);
if ($currentuser->login())
{
// set cookies for login info
header(”Location:/main.php”);
exit();
}
else
{
header(”Location:/login.php?error=1″);
exit();
}
?>

Is This Answer Correct ?

45 Yes

4 No

What do you mean by MVC ?..

Answer / kiran sharma

MVC means Model View Controller .
this thing is little-bit hard to learn than normal programming.
You have to create Object and Classes and You can access as
you want in your application .

M : Model - Model means backend database You use in web .
V : View - View meand user interface .
C : Controller - means control all web functions .

for small application it is better to use normal programming
rather than MVC , but it is better for large and more secure
applications .

Thanks ,
Kiran Sharma .

Is This Answer Correct ?

23 Yes

3 No

What do you mean by MVC ?..

Answer / guest

Model View Controller

Is This Answer Correct ?

20 Yes

7 No

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