StructureMap
If you haven’t heard about dependency injection, it is something you should definitely look into. It can save tons of time when coding.

StructureMap is a dependency injection framework that makes it easy to create new instances of objects and even cache an instance of an object so various references to the object use the same instance. This is very useful with objects such as database connections.

You can download the library from the StructureMap Home Page. The example used in this post is using StructureMap 2.6.1.  I’m also using Visual Basic.  I had a tough time finding information on how to use StructureMap with Visual Basic, so hopefully, this will help someone else.

Setting Up MVC
When using StructureMap with ASP.NET MVC 1.0, I’ve found it works best if a folder is created in each project; Main, Data, and Service; where the StructureMap files are stored. This keeps them organized and makes them easy to find as you need to update them. A reference to the StructureMap DLL will need to be added to each project as well.

In the main project’s StructureMap folder, the following files are needed:

StructureMapControllerFactory

Imports System.Web.Mvc
Imports StructureMap

Public Class StructureMapControllerFactory
    Inherits DefaultControllerFactory

    Protected Overrides Function GetControllerInstance(ByVal controllerType As System.Type) As System.Web.Mvc.IController

        Return ObjectFactory.GetInstance(controllerType)

    End Function

End Class

This class sets up a factory class to get an instance of the StructureMap factory. It will be used to replace MVC’s default controller factory so that StructureMap will be in charge of creating our controllers.

BootStrapper

Imports StructureMap
Imports YourProject.Data
Imports YourProject.Services

Public Class BootStrapper

    Public Shared Sub ConfigureStructureMap()

        ObjectFactory.Initialize(AddressOf StructureMapRegistry)

    End Sub

    Private Shared Sub StructureMapRegistry(ByVal x As IInitializationExpression)

        x.AddRegistry(New MainRegistry())
        x.AddRegistry(New DataRegistry( _ ConfigurationManager.ConnectionStrings("iSeries").ConnectionString, _ ConfigurationManager.ConnectionStrings("Interbase").ConnectionString))
        x.AddRegistry(New ServiceRegistry())
        x.Scan(AddressOf StructureMapScanner)

    End Sub

    Private Shared Sub StructureMapScanner(ByVal scanner As StructureMap.Graph.IAssemblyScanner)

        scanner.Assembly("YourProjectNamespace")
        scanner.Assembly("YourProjectNamespace.Data")
        scanner.Assembly("YourProjectNamespace.Services")
        scanner.WithDefaultConventions()

    End Sub
End Class

This class is where StructureMap is configured. Within the StructureMapRegistry method, each AddRegistry call is made to include each of our project’s registry files, which have yet to be created. We will get to that in a moment, but notice that the DataRegistry is accepting values for connection strings. This is how information can be passed into a class being created by StructureMap when you would like to keep the configuration settings within the Web.config file.

Also, within the StructureMapScanner method, an entry needs to be made to scan each project’s namespace.

MainRegistry

Imports DCS.Data
Imports StructureMap.Configuration.DSL

Public Class MainRegistry
    Inherits Registry

    Public Sub New()

        [For](Of IWebContext)() _
            .Use(Of WebContext)()

    End Sub

End Class

Each project will have its own registry file where you can specify that Interface-A should create an instance of Class-A. In the example above, I want StructureMap to create an instance of WebContext (from the main project) when it comes across a reference to IWebContext. 

In the Data project’s StructureMap folder you will need:

DataRegistry

Imports StructureMap.Configuration.DSL
Imports Spartan.DAO.Database

Public Class DataRegistry
    Inherits Registry

    Public Sub New(ByVal iSeriesConnectionString As String, ByVal interbaseConnectionString As String)

    'Data Connections.
    [For](Of YourDataContext)() _
        .HybridHttpOrThreadLocalScoped _
        .Use(Function() New YourDataContext())

    [For](Of DB2Connection)() _
        .HybridHttpOrThreadLocalScoped _
        .Use(Function() New DB2Connection(iSeriesConnectionString))

    [For](Of InterbaseConnection)() _
        .HybridHttpOrThreadLocalScoped _
        .Use(Function() New InterbaseConnection(interbaseConnectionString))

    'Repositories.
    [For](Of IShiftRepository)() _
        .Use(Of ShiftRepository)()

    End Sub

End Class

The DataRegistry is interesting because we are passing in two connection strings from the Web.config file. The first data connection is for Microsoft SQL, the second for DB2 and the third for Interbase. The second and third are using the DB2Connection and InterbaseConnection classes which are home grown database connection class that I wrote.  All three of these database connections are being cached by using the .HybridHttpOrThreadLocalScoped property. Using this will make the database cached instance work for both your live program and your unit testing.

The entry under repositories is what all remaining entries would look like within the registry class. Since the data project contains our repositories, they would all be listed here.

And, in the Service project’s StructureMap folder you will need:

ServiceRegistry

Imports StructureMap.Configuration.DSL

Public Class ServiceRegistry
    Inherits Registry

    Public Sub New()

        [For](Of IShiftService)() _
        .Use(Of ShiftService)()

    End Sub

End Class

The service registry is similar to that of the main project. All service classes found in the service project would be listed here.

Changes to the Global.asax

The last thing to do is setup the Global.asax file to load StructureMap.  Make the following changes to the Application_Start method:

Sub Application_Start()

    RegisterRoutes(RouteTable.Routes)

    'StructureMap
    BootStrapper.ConfigureStructureMap()
    ControllerBuilder.Current.SetControllerFactory(New StructureMapControllerFactory())

End Sub

Now, the default controller factory used by MVC will be overridden by our StructureMapControllerFactory. When a controller is created, it will now use StructureMap.

So, how do you use this when creating a class? This is the easy part.

StructureMap will use the greediest constructor from your controller, meaning, if you have two constructors, the one with the most parameters will be used. Each parameter references an Interface and sets a class variable for the object.  StructureMap uses the registry classes that we setup to map an interface to a real object.

Example Controller

Imports YourProject.Data
Imports YourProject.Services
Imports StructureMap

Public Class ExampleController
    Inherits System.Web.Mvc.Controller

    Private _shiftService As IShiftService
    Private _webContext As IWebContext

    Public Sub New( _
        ByVal shiftService As IShiftService, _
        ByVal webContext As IWebContext)

        _shiftService = shiftService
        _webContext = webContext

        'Initialize service classes.
        _shiftSummaryService.Initialize(New ModelStateWrapper(Me.ModelState))

    End Sub

    ...

All that you need to do is create a constructor, pass in all the interface references you need for the controller, then store them in a class variable. If you need to use the ModelState for validation within your service class, the best way I’ve found to do this is use an Initialize function in your service class to pass in the ModelState. This is because the ModelState is not yet created by MVC when the service classes are created by StructureMap.

When StructureMap creates the instance of the ShiftService, it will look at the greediest constructor from that class to create instances for any required parameters. This continues for all classes that are referenced.

Once the solution has been configured to use StructureMap, the only thing you’ll need to maintain will be the registry files as you add new classes and interfaces to your project. Don’t forget to add a registry entry or you will recieve an exception.