Lære What MVC Solves | Introduction to MVC

Definition

Definition: MVC (Model-View-Controller) is a design pattern that separates an application into three interconnected components: the Model (handles data and business logic), the View (manages the user interface), and the Controller (coordinates input and updates between the Model and View).

When you first start building PHP web applications, it's common to mix all your code, HTML, PHP logic, and even database operations, into a single file. This approach might work for very small projects, but as your application grows, it quickly leads to problems. Mixing everything together makes your code hard to read, difficult to maintain, and nearly impossible to update or debug without breaking something else. This is called a monolithic codebase, where responsibilities are not clearly separated. MVC addresses these issues by introducing a clear separation of concerns. By dividing your application into three distinct parts, you can organize your code so that each part has a single responsibility. This makes your application easier to maintain, test, and extend over time.

index.php


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<?php
// Connect to database
$conn = mysqli_connect('localhost', 'user', 'pass', 'test');

// Fetch user
$result = mysqli_query($conn, "SELECT name FROM users WHERE id = 1");
$user = mysqli_fetch_assoc($result);

// Display HTML with embedded PHP
?>
<!DOCTYPE html>
<html>
<head><title>User Page</title></head>
<body>
  <h1>Welcome, <?php echo $user['name']; ?>!</h1>
</body>
</html>

In the example above, everything is handled in a single file. The PHP code connects to the database, fetches data, and outputs HTML all at once. This might seem convenient at first, but it quickly becomes unmanageable. If you want to change how data is displayed, you have to dig through database code and HTML mixed together. Testing or reusing the logic elsewhere is difficult, and fixing bugs can accidentally break unrelated parts of your application.

view.php

logic.php


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<!DOCTYPE html>
<html>
<head><title>User Page</title></head>
<body>
  <h1>Welcome, <?php echo htmlspecialchars($name); ?>!</h1>
</body>
</html>

By splitting the logic and presentation into separate files, you create a structure that is much easier to manage. The logic.php file is responsible only for fetching the data, while view.php handles how that data is displayed. This separation means you can update the HTML without touching the database code, and vice versa. Over time, this leads to cleaner, more maintainable code that is easier to debug, test, and extend as your application grows.

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