The goal of this tutorial is to describe one method of performing validation in an ASP.NET MVC application. In this tutorial, you learn how to move your validation logic out of your controllers and into a separate service layer. If you’re looking for ASP.NET MVC hosting, you can choose ASPHostDirectory as the alternatives. Only with $ 3.99/month, you can get this application. So, what are you waiting for?
Separating Concerns
When you build an ASP.NET MVC application, you should not place your database logic inside your controller actions. Mixing your database and controller logic makes your application more difficult to maintain over time. The recommendation is that you place all of your database logic in a separate repository layer.
For example, Listing 1 contains a simple repository named the ProductRepository. The product repository contains all of the data access code for the application. The listing also includes the IProductRepository interface that the product repository implements.
Listing 1 - Models\ProductRepository.vb
Public Class ProductRepository
Implements IProductRepositor
Private _entities As New ProductDBEntities()
Public Function ListProducts() As IEnumerable(Of Product) Implements IProductRepository.ListProducts
Return _entities.ProductSet.ToList()
End Function
Public Function CreateProduct(ByVal productToCreate As Product) As Boolean Implements IProductRepository.CreateProduct
Try
_entities.AddToProductSet(productToCreate)
_entities.SaveChanges()
Return True
Catch
Return False
End Try
End Function
End Class
Public Interface IProductRepository
Function CreateProduct(ByVal productToCreate As Product) As Boolean
Function ListProducts() As IEnumerable(Of Product)
End Interface
The controller in Listing 2 uses the repository layer in both its Index() and Create() actions. Notice that this controller does not contain any database logic. Creating a repository layer enables you to maintain a clean separation of concerns. Controllers are responsible for application flow control logic and the repository is responsible for data access logic.
Listing 2 - Controllers\ProductController.vb
Public Class ProductController
Inherits Controller
Private _repository As IProductRepository
Public Sub New()
Me.New(New ProductRepository())
End Sub
Public Sub New(ByVal repository As IProductRepository)
_repository = repository
End Sub
Public Function Index() As ActionResult
Return View(_repository.ListProducts())
End Function
'
' GET: /Product/Create
Public Function Create() As ActionResult
Return View()
End Function
'
' POST: /Product/Create
<AcceptVerbs(HttpVerbs.Post)> _
Public Function Create(<Bind(Exclude:="Id")> ByVal productToCreate As Product) As ActionResult
_repository.CreateProduct(productToCreate)
Return RedirectToAction("Index")
End Function
End Class
Creating a Service Layer
So, application flow control logic belongs in a controller and data access logic belongs in a repository. In that case, where do you put your validation logic? One option is to place your validation logic in a service layer.
A service layer is an additional layer in an ASP.NET MVC application that mediates communication between a controller and repository layer. The service layer contains business logic. In particular, it contains validation logic.
For example, the product service layer in Listing 3 has a CreateProduct() method. The CreateProduct() method calls the ValidateProduct() method to validate a new product before passing the product to the product repository.
Listing 3 - Models\ProductService.vb
Public Class ProductService
Implements IProductService
Private _modelState As ModelStateDictionary
Private _repository As IProductRepository
Public Sub New(ByVal modelState As ModelStateDictionary, ByVal repository As IProductRepository)
_modelState = modelState
_repository = repository
End Sub
Protected Function ValidateProduct(ByVal productToValidate As Product) As Boolean
If productToValidate.Name.Trim().Length = 0 Then
_modelState.AddModelError("Name", "Name is required.")
End If
If productToValidate.Description.Trim().Length = 0 Then
_modelState.AddModelError("Description", "Description is required.")
End If
If productToValidate.UnitsInStock
The Product controller has been updated in Listing 4 to use the service layer instead of the repository layer. The controller layer talks to the service layer. The service layer talks to the repository layer. Each layer has a separate responsibility.
Listing 4 - Controllers\ProductController.vb
Public Class ProductController
Inherits Controller
Private _service As IProductService
Public Sub New()
_service = New ProductService(Me.ModelState, New ProductRepository())
End Sub
Public Sub New(ByVal service As IProductService)
_service = service
End Sub
Public Function Index() As ActionResult
Return View(_service.ListProducts())
End Function
'
' GET: /Product/Create
Public Function Create() As ActionResult
Return View()
End Function
'
' POST: /Product/Create
<AcceptVerbs(HttpVerbs.Post)> _
Public Function Create(<Bind(Exclude := "Id")> ByVal productToCreate As Product) As ActionResult
If Not _service.CreateProduct(productToCreate) Then
Return View()
End If
Return RedirectToAction("Index")
End Function
End Class
Notice that the product service is created in the product controller constructor. When the product service is created, the model state dictionary is passed to the service. The product service uses model state to pass validation error messages back to the controller.
Decoupling the Service Layer
We have failed to isolate the controller and service layers in one respect. The controller and service layers communicate through model state. In other words, the service layer has a dependency on a particular feature of the ASP.NET MVC framework.
We want to isolate the service layer from our controller layer as much as possible. In theory, we should be able to use the service layer with any type of application and not only an ASP.NET MVC application. For example, in the future, we might want to build a WPF front-end for our application. We should find a way to remove the dependency on ASP.NET MVC model state from our service layer.
In Listing 5, the service layer has been updated so that it no longer uses model state. Instead, it uses any class that implements the IValidationDictionary interface.
Listing 5 - Models\ProductService.vb (decoupled)
Public Class ProductService
Implements IProductService
Private _validatonDictionary As IValidationDictionary
Private _repository As IProductRepository
Public Sub New(ByVal validationDictionary As IValidationDictionary, ByVal repository As IProductRepository)
_validatonDictionary = validationDictionary
_repository = repository
End Sub
Protected Function ValidateProduct(ByVal productToValidate As Product) As Boolean
If productToValidate.Name.Trim().Length = 0 Then
_validatonDictionary.AddError("Name", "Name is required.")
End If
If productToValidate.Description.Trim().Length = 0 Then
_validatonDictionary.AddError("Description", "Description is required.")
End If
If productToValidate.UnitsInStock
The IValidationDictionary interface is defined in Listing 6. This simple interface has a single method and a single property.
Listing 6 - Models\IValidationDictionary.cs
Public Interface IValidationDictionary
Sub AddError(ByVal key As String, ByVal errorMessage As String)
ReadOnly Property IsValid() As Boolean
End Interface
The class in Listing 7, named the ModelStateWrapper class, implements the IValidationDictionary interface. You can instantiate the ModelStateWrapper class by passing a model state dictionary to the constructor.
Listing 7 - Models\ModelStateWrapper.vb
Public Class ModelStateWrapper
Implements IValidationDictionary
Private _modelState As ModelStateDictionary
Public Sub New(ByVal modelState As ModelStateDictionary)
_modelState = modelState
End Sub
#Region "IValidationDictionary Members"
Public Sub AddError(ByVal key As String, ByVal errorMessage As String) Implements IValidationDictionary.AddError
_modelState.AddModelError(key, errorMessage)
End Sub
Public ReadOnly Property IsValid() As Boolean Implements IValidationDictionary.IsValid
Get
Return _modelState.IsValid
End Get
End Property
#End Region
End Class
Finally, the updated controller in Listing 8 uses the ModelStateWrapper when creating the service layer in its constructor.
Listing 8 - Controllers\ProductController.vb
Public Class ProductController
Inherits Controller
Private _service As IProductService
Public Sub New()
_service = New ProductService(New ModelStateWrapper(Me.ModelState), New ProductRepository())
End Sub
Public Sub New(ByVal service As IProductService)
_service = service
End Sub
Public Function Index() As ActionResult
Return View(_service.ListProducts())
End Function
'
' GET: /Product/Create
Public Function Create() As ActionResult
Return View()
End Function
'
' POST: /Product/Create
<AcceptVerbs(HttpVerbs.Post)> _
Public Function Create(<Bind(Exclude := "Id")> ByVal productToCreate As Product) As ActionResult
If Not _service.CreateProduct(productToCreate) Then
Return View()
End If
Return RedirectToAction("Index")
End Function
End Class
Using the IValidationDictionary interface and the ModelStateWrapper class enables us to completely isolate our service layer from our controller layer. The service layer is no longer dependent on model state. You can pass any class that implements the IValidationDictionary interface to the service layer. For example, a WPF application might implement the IValidationDictionary interface with a simple collection class.
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