MVC (Model-View-Controller)

MVC (Model-View-Controller) is an architectural pattern that splits an application into three parts: the model, which holds data and business rules; the view, which presents data to the user; and the controller, which receives input and coordinates the other two.

Why it matters

Separating these responsibilities makes code easier to test and change. A designer can rework a view without touching business logic, and the same model can serve a web page, an API and a command-line tool. MVC is the basis of frameworks such as Ruby on Rails, Django (which calls it MVT), ASP.NET MVC and Laravel. Variants like MVP and MVVM adapt the idea to user interface frameworks.

Example

A request to /sites/42 in a typical web framework:

1. The router sends it to SitesController.show.
2. The controller asks the Site model for record 42.
3. The controller passes the record to the show view template.
4. The view renders HTML, which is returned to the browser.

Common mistakes

• Putting business logic in controllers ("fat controller") or in views.
• Letting the view query the database directly.
• Assuming every framework defines MVC the same way; the exact roles differ.

Related

• Design pattern
• Back end
• Front end
• CRUD

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