Question

I have for one customer entity multiple viewmodels depending on the existing views like Create,Update,Get,Delete. These viewmodels share the same properties up to 75% with the entity.

Should I better merge all the customer viewmodels to one big viewmodel?

So I have to map only and always from one entity to one viewmodel and the way back?
Do you see any disadvantage in flexibility for certain scenarios I have not in my mind now?

Answer 1

In the long run, keeping them separate will be better because while the data contained in each ViewModel may be similar or even identical, the intention is different. For example, the Create and Update ViewModels are certainly similar, but have a few important differences. First, the Create view model usually doesn’t have the identity of the entity and having it there may be confusing since it doesn’t make sense. Second, if the application supports partial updates, the update ViewModel may be a collection of changes to an existing entity, not the entity as a whole.

If you are striving for DRY you can achieve re-usability by means other than sharing the entire ViewModel class. Instead, you can create smaller re-usable components and re-use by composition instead of inheritance. Attempting to coerce a single ViewModel class to fulfill all requirements will be buggy beacause the code is more difficult to reason about. Many times, simple copy & paste gets the job done better than what OOP offers.