understanding mvc: difference between a library class and a model class

Question

so i want to follow the mvc conventions but haven't really got the hang of it.

i've got problem understanding the explicit difference between a model and a library class and how they relate to each other.

eg. i want to create classes to add/edit contacts and also adding them to a group.

i thought it should be divided into 2 classes: Contact and Group.

The first class would create a contact. The other one will add the contact to a group. I thought this dividing would be perfect cause their logic is isolated from each others. Contact doesn't care if Group exists or not. Group doesn't care about how a Contact looks like.

So Contact will have these methods:

$Contact->add($name, $email, $address, $phone) // create an entry in database
$Contact->delete($id) // delete the entry in database
$Contact->edit($id, $name, $email, $address, $phone) // edit the entry in database

And Group:

$Group->createGroup($name) // create a group in database
$Group->delete($id) // delete a group in database
$Group->addContact($groupId, $contactId) // add a contact to a group in database

So these classes apparently work with the database. Does this mean that these are models? Or are they library classes that eg. should be put in SYSTEM/LIBRARIES in CodeIgniter. If it's the latter one, how do a Model in this case looks like using the classes?

And how would a controller look like in this scenario?

Would be great if someone could give me the big picture! Thanks!

Answer 1

The MVC pattern does not have the concept of a Library. What you are refering to is a general usage pattern of MVC frameworks. That is having a model folder, which contains application specific classes often derived from generic, reusable and application independent library classes.

Answer 2

Generally Models are like objects, they interact with the database, have variables and functions, and are reusable.

Libraries are normally sets of helper functions to process data / perform actions.