I've always used the model as something to more or less store and execute database queries. I have heard about the fat model, thin controller concept.
The way I setup my models right now causes a lot of junk in controllers for things like validating forms, formatting data. Does form validation, file uploading and data formatting belong in the controller or the model?
I realize this question is subjective, which should create some good discussion rather than a concrete answer.
Form Validation should definitely be part of the model. I generally represent each form as one model and pass it the sanitized post/get paramaters. The model can then take whatever action is necessary based on the input and use a property (optionally with a getter) to signal success or failure. In psuedo code you want it to look something like:
class Controller
{
function action()
{
$input = new Input();
$form = new FormModel($input);
if ($errors = $form->errors())
{
//load the appropriate view for the errors
}
else
{
//load the appropriate view for success with an optional redirect
}
}
The model is what interacts with the data (most often a database). Controllers use the models to access the data.
You have two main roads to go. Thin controller/fat model or fat controller/thin model. Basicly is were you put most of the interaction. I prefer to keep at the model the major portion of the code. That way, the code is available in virtually every controller and/or lib. If the code remain at controller, it's hard (but not impossible) to use it in other controllers.
Things lije validations and other common tasks should be in a lib or helper. You can produce a set of "workers" (this is the name I give to them) to do the heavy lifting. Also, CI has a LOT of ready made libs and helpers both from the CI team and the community. Mess around the wiki to find the wealth of information available.
Hope this helps Vx