Entity vs Model vs View Model
asp.net-mvc, c#, entity-framework, mvvm
Solution
Different people understand these terms a bit differently, but this is how I understand it:
Entity - object that has an identity (ID), usually comes from a database. Pretty simple class.
Model - any business object, this is a kinda broad term. It can be an entity, some custom class you've created in your project etc.. It's pretty much everything that isn't a view nor a controller/viewmodel.
ViewModel - some kind of a mediator between a model and the view. It modulates the communication between the model and the view, for instance applies validation, combines more models into one bigger object etc., for the purposes of the interaction with the specific view. ViewModel is also responsible for event handling (button mouse clicks for instance), so it exposes commands to the view you bind to (WPF).
Problem
I just spent some time reading about these terms (I don't use them that much since we don't have any MVC applications and I usually just say "model"), but I have the feeling these means different things depending on the context: Entity This is quite simple, it is one row in the database: - In relation to a database , an entity is a single person, place, or thing about which data can be stored. Model I often read, this is basically a combination of entities to represent a full set of data, let's say an Addresslist-model of a customer would combine the entities customer, address and probably individual. Viewmodel A term in the MVVM or MVC patterns, which is a model, which represents exactly the data you can see on the view. The viewmodel is on the application tier and has attributes for validation, e.g. ASP.NET MVC Model vs ViewModel From my sight, these terms seem all a bit redundant: The Viewmodel has obviously his use, otherwise the view would have to do all the hard work to show the right stuff. The entity is just the representation, as we know from the EF, but if you combine these two, where has the model his use? Stuff like validation, security etc. has to be done on the ViewModel. Would you use the model when you have hundreds of small tables to put another abstraction between the entities and the viewmodel? Or Are in terms of MVC and MVVM entities and models usually the same? As usual thanks and a nice weekend Matthias