Question

i am a complete newbie to the entity framework,mvc just started with it 3 weeks ago.
From then i have been beating around the bush searching for the right approach.the more i dig the more i get lost…i am afraid that i could not proceed any further with using entity framework in mvc

I m lost and frustrated 🙁

what i have been trying to do is to use entity framework for the MVC application.For that i have started with creating an School.edmx file(which has School.Designer.cs automatically created for it.I dont have any POCO or any others just plain edmx with designer class).Then through some searching i have found that its bad practice to use entity object as model for view…..

Now the real thing started i have made a viewmodel for an entity object.The thing is i dont really get why i have to use a repository and why do i have to map my entity objects and viewmodel objects.Everytime i search why i have to map i get some links saying how to use automapper and the more i search about repository the more i get lost .i dont even understand it.why do i have to map …??? and why do i have to use repository.

And now the other thing i ask repeatedly to myself is why do i have to write data annotation again in the Viewmodel class when i have already data annotated it in my designer.cs file (like [Required],[Email] and other annotations)..? WHY to write them again!! (If i dont mention them in viewmodel i dont see the annotations working). Duplication of annotation…?

I am lost and i dont even know where i m now
someone give me the right path to follow

Yours Sincerely,

Lost & Confused Newbie

Answer 1

The thing is i dont really get why i have to use a repository

MVC helps you write code that has a clear separation of concerns. In this case, the repository is meant to how the application interacts with the data storage for a specific entity. If you want a Student entity you call StudentRepository.GetEntity(). If you want to save to save you call the StudentRepository.SaveEntity(Student student).

Why do i have to map my entity objects and viewmodel objects.Everytime i search why i have to map i get some links saying how to use automapper and the more i search about repository the more i get lost.

While you can use these entities directly in your view for simple cases, the problem comes up when you have more complex views – composite views that may need multiple entities, views that need to expose only a subset of an entity or even a subset of multiple entities. So yes, you can just expose your entity directly but I find it easier just to create a separate view model.

Automapper is used to help map from view model to entity. So, instead of writing a lot of

entity.Name = viewModel.Name;
entity.Age = viewModel.Age;
...

Automapper is used to automatically map these properties.

And now the other thing i ask repeatedly to myself is why do i have to write data annotation again in the Viewmodel class when i have already data annotated it in my designer.cs file (like [Required],[Email] and other annotations)..?

You should specify validation logic specific for each view in the view model so that if validation fails at the controller it can stop processing instead of continuing. Even though mapping your view model to an entity and trying to save would be prevented by the entities data annotation, I find it clearer to look at a view and its view model to understand what’s going on instead of going from view to view model to entity.

Update:

Take a look at ASP.NET MVC View Model Patterns and How we do MVC – View models. I found them both useful when trying to understand view models.