I'm getting some trouble understanding the MVC concepts.
I'm building a User model, you know? Application_Model_Users. They say that the models should only contain the structure... and the business logic should be put in the controller.
So, consider a function called authenticate($user, $password). This function will return true if the username and password entered is valid or false otherwise. Where should I put this function? In the controller Authentication or in the model Users?
Thank you!
Related to the Model, whenever you need to retrieve data(from DB, Web service, filesystem) or save data, you need a model to do the job. In MVC, a model is not understood as a mapped table, maybe more like a mapper. Zend has some info about this at their site, it could help you understanding mvc a bit more.
When it comes to user authentication, you should certainly implement the authenticate function inside the Users model, I would think you will do a database check against a table or similar. Just in case you are not already using it, Zend comes with a package for auhtentication: Zend_Auth (http://framework.zend.com/manual/en/zend.auth.html) , it could speed up implementing the security at your application.
Although Model operations often include storage operations (DB, servicer, etc), it is not limited to that. Model, as far as I know, should countain Business logic entities, this is, classes that represent your business entities, like User, Person, Customer, etc. Each class should define its own operation methods, in example, a Person model class should allow you to get a person's name, calculate his/her age according to his/her birth date, etc.
Also, there should be specialized classes for Model storage and retrieval. With these classes you could fetch all your Customers, or only one, using certain conditions, etc, or save a modified Customer class instance (in example, a customer changed his/her address or phone number).
This separates the storage/retrieval operations from Business login operations.
So, according to your question, your model could have a class that allows you to find one user by its user name and password. If the user is found, you could return a Model_User class instance (in example). Then, using the standard Zend_Auth class, or extending it to create your own authentication class, you can use some Login form parameters to perform the user authentication.
Follow the Zend Framework quick start guide, there are the basics about MVC in Zend Framework. Also, there you will find some resources about Zend_Db and related classes, to allow DB interaction. There are also Zend_Db_Table, Zend_Db_Table_Rowset and Zend_Db_Table_Row classes, that you could extend to fit your model storage needs.
I have a personal solution where I extend Zend_Db_Table for my (in example) Model_UserTable class, used to store or query my Model_User entities. And my Model_User class extends Zend_Db_Table_Row.
