What is the right way to handle $_POST data in MVC?

Question

I have the common MVC situation in my PHP system: the Controller receive a request from the View containing $_POST data. Now I have th

Answer 1

Once upon a time was the three tiered application architecture.

It all depends on your MVC framework. Normally, the Controller does the link between the user and the model layer, which manipulate domain objects.

In the early days of MVC in PHP, the model layer was actually just the domain objects, called models for that purpose. Some prefered having so called thin models, which only provide an OO representation of the data, (which simplifies persistence). In that case, the controller would regroup the so called actions, containing the bulk of the processing associated with an HTTP request (fat controller).

Others embedded most of said processing in the object model with dedicated methods (fat model).

However, at some point, you have to analyse the content of the query to sanitize and validate it, and this depends on how your view will format the request. Sanitization might be a controller task (this request should only contain these values), while validation is definitely a model task (values should be of these types).

An interesting question is: how do you deal with actions impacting several domain objects? Where do you put the logic for that?

Nowadays, the model layer is composed of services segregating the domain objects from the evil grasp of the controllers, to limit the dependencies between the layers to their respective interfaces only. This is where most of the request processing is done.

Symfony2, for instance, provides a sensible answer to this question: each step of the processing of a request is implemented in a dedicated piece of code, which could be described as the following:

• the request is first turned into an object
• that object is routed using a routing object
• it is handled to a controller
• the controller pass the request to the service concerned by the action, which build the response object

The service job is then broken in several steps:

• validation (using a dedicated object which rely on rules described in a separate file),
• construction/updating of domain objects (using serialization to/from db if necessary),
• selection of a template for the response,
• population of said template with the relevant data from the domains.

CakePHP is another popular framework which follows similar concepts: simple controllers, and services encapsulating domain objects.

See this question for a better insight on the general concepts.

See this other question for other answers.

Thanks to tereško for his invaluable input on the matter.