CODEWITHSUNDEEP
c#asp.net-mvc
dc922
dc922

Reputation: 639

How does ViewModel work in MVC

I really can't get my head around how to use ViewModel's in MVC. Say I have two simple domain models: 

public class Customer
{
    public int Id { get; set; }
    public string CustomerName { get; set; }
}

 public class Order
{
    public int Id { get; set; }
    public string ProductName { get; set; }
}

And now my goal would be to create a ViewModel that displays (combines) the CustomerName and ProductName to display to a view. I'm confused what to include in the ViewModel to accomplish this. Do I use the same property names as my domain models like so? 

public class MyViewModel
{
    public string CustomerName { get; set; }
    public string ProductName { get; set; }
}

How does the ViewModel know that the properties come from two different classes? Or am I forming my ViewModel incorrectly?

Upvotes: 3

Views: 1063

Answers (4)

alexo
alexo

Reputation: 934

As i can see it you have a bigger design problem here.

Lets say you need to show on the UI only the CustomerName and ProductName. Well then just add those two on to your ViewModel class and you`re good to go, exactly how you described it.

public class MyViewModel
{
    public string CustomerName { get; set; }
    public string ProductName { get; set; }
}

Getting the data in two variables is not a problem:

Customer customer = service.GetCustomer();
Product product = service.GetProduct()

And now that you have everything you need you can just set the data and pass it to the view.

MyViewModel viewModel = new MyViewModel();
viewModel.CustomerName = customer.CustomerName;
viewModel.ProductName = product.ProductName;

It always depends on what you need to show on the UI and only send what you need and nothing more. You do not need to have exactly one Model that you pass all over the place in your application, Business, DataAccess, UI. You can have something custom if you really need it.

Upvotes: 3

Max Bertoli
Max Bertoli

Reputation: 614

ViewModel rapresents a model you use to go to your view. In your controller you'll retrieve data and pass them to your ViewModel.

Imagine you have a checkbox in you view that rapresent a Gold Customer: it's not suitable to change your domain model to add this information and it's not a good practice to make your code dirty with Viewbag and Viewdata (imho).

So you create a model or template that has all the information you need. In our case:

public class MyViewModel
{
    public string CustomerName { get; set; }
    public string ProductName { get; set; }
    public boolean IsGoldCustomer { get; set; }
}

Ofter you'll have to convert your model into a ViewModel and viceversa in order to pass data from a "DOMAIN model" to a "VIEW model".

Upvotes: 0

Darren
Darren

Reputation: 70776

You would have to set this up yourself in the ViewModel, as a template it could look something like:

public class MyViewModel
{
    public string CustomerName { get; set; }
    public string ProductName { get; set; }

    public void GetCustomerName(int customerId) 
    {
       CustomerName = CustomerServiceLayer.GetCustomerName(customerId);
       // CustomerService Layer (I.e. a repository that contains this info;
    }

    public void GetProductName(int productId) 
    {
       ProductName = ProductServiceLayer.GetProductName(productId); 
       // ProductService Layer (I.e. a repository that contains this info;
    }

}

You would then have two other Service Layers (ProductServiceLayer and CustomerServiceLayer) that speak to the database/repository to obtain the information you want. That information is then returned to the view (via your ViewModel) and displayed to the user.

Alternatively you could pass a Customer and a Product object directly into your ViewModel (via a constructor).

public class MyViewModel 
{
    public Customer MyCustomer { get; set; }
    public Product MyProduct { get; set; }

    public MyViewModel(ICustomer customer, IProduct product) 
    {
       MyCustomer = customer;
       MyProduct = product;
    }
}

The downfall here would be that you expose your entire Customer and Product classes in the View.

Upvotes: 2

Gareth Hopkins
Gareth Hopkins

Reputation: 354

You can do it like that but you generally build the viewmodel up on render in the get action and then post parts of that view model back and handle it on a post action. The MVC binding does the magic once getting the values posted back from a form.

I wouldn't put business logic inside the viewmodel but rather build the viewmodel up in your controller using managers/services.

You could also make it so the viewmodel has your complex model types as the properties like so..

public class MyViewModel
{
    public Customer Customer { get; set; }
    public Product Product { get; set; }
}

Upvotes: 1

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