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I can't quite figure out how to get the view model to be notified of changes in the model without adding a bunch of UI specific stuff like INotifyProperyChanged and INotifyCollectionChanged in my model or create tons of different events and do a bunch of things that feel like they're UI specific and should stay out of the model.
Otherwise I'd just have to duplicate all the business logic in the view-model to make sure everything is up to date, and then what's the point of having the model then?
One of the tricky ones that I have in my model is a property of a "Category" class. You can think of it as a tree structure and the property is all leaf-node descendants. Well in the model that property is generated on the fly recursively through all it's children, which is all fine and good. The view-model however needs to bind to that property and needs to know when it changes. Should I just change the model to accommodate the view-model? If I do then the view-model doesn't really do anything at this point, the model raises all the necessary notifications of changes and the view can just bind straight to the model. Also if the model was something I didn't have the source to, how would I get around this?
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In MVVM, the business logic is built into the Model. The ViewModel is there to bridge between the View and the Model, so it's logic only pertains to driving the display and updating the model from user interactions with the View.
A1: Business Logic goes to Model part in MVC . Role of Model is to contain data and business logic. Controller on the other hand is responsible to receive user input and decide what to do. A2: A Business Rule is part of Business Logic .
Business logic. The model in MVC should also be able to implement business logic on the data it represents. For example, common business logic for web applications includes validation rules.
The business logic should be placed in the model, and we should be aiming for fat models and skinny controllers. As a start point, we should start from the controller logic. For example: on update, your controller should direct your code to the method/service that delivers your changes to the model.
I disagree that INotifyPropertyChanged and INotifyCollectionChanged are UI-specific. They are in namespaces and assemblies that are not tied to any particular UI stack. For that reason, I typically put that kind of behavior as low in the system as I can (usually the data layer).
If there's some reason you don't want to put it at that level, that's fine. You can put it in at a higher level such as the service or UI layer. However, you need to make sure all changes to the data structures occur through that layer also.
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