最佳实践实体框架模型与ViewModels

Question

From what I read, I understand that we should always pass a viewmodel to the view. However, sometimes this viewmodel is exactly or almost the same as the EF-model. Is it acceptable or is there any workaround to this problem (repetitive code) ?

For example, if I have this EF-Model :

class UserModel
{
    string id {get;set}
    string name {get;set}
    string address {get;set}
    string phone {get;set}
    string website {get;set}
}

How should the viewmodel be ... like this :

class UserViewModel
{
    string name {get;set}
    string address {get;set}
    string otherobject {get;set}
}

Or Like this :

class UserViewModel
{
    UserModel user;
    string otherobject {get;set}
}

With option #1, properties are repeated... and in another viewmodel they will be repeated again. And I will need to repeat all data annotations on each viewmodels. However, I send only the properties that I need.

With option #2, nothing is repeated, but I pass a lot of properties that I don't need.

The last option would be to mix option #1 and option #2 according to the needs... but I don't like this option because of the lack of a common standard. Sometimes the properties will be defined and datannoted in the viewmodels and sometimes in the EF-model.

I wish there is an option #4 that I don't see...?

Thank you.

Answer 1

The difference of those classes is how your application interacts with. Model and ViewModel has different audience.

Your Models should be interacting with your application, and sometimes many people prefer to use those models as entities in EF Code First. They are what we call Domain Objects.

On the other hand, ViewModels should be interacting with your Views. In your service layer, you populate your ViewModel with some data, and you can access them from your controllers.

However, sometimes this viewmodel is exactly or almost the same as the EF-model.

The keyword here is "sometimes". You are right, for a very simple application, you don't even need to think about ViewModels , where your models can simply be used in most cases. However, think about some cases for example where you want to display list of latest posts , latest comments , and let's say some related posts on a single view. What you are going to do? This is where the ViewModels come. You pass a specific ViewModel to your view, that contains all the necessary data, posts, comments, and related posts.

In most cases, you ViewModel should be build up from multiple Models , and sometimes, the porperties of a ViewModel are type of Models

Answer 2

I know it has been quite sometime since this question was asked. But, this may help someone who is looking for the answer.

Eventhough you have ViewModels which are almost same as models, it is recommended to create ViewModels with same code.

Possible reasons are

1. You may want to add validation to properties using Data Annotations. It is not advised to have validation which are more specific to screen in your models which are supposed to be reflections of your DB structure.

2. Your ViewModels may change in future. It may not make sense now, but there is always a possibility.

If you are worried about mapping code which looks obvious in most of the cases, you can make use of Automapper.

Cheers!