StructureMap IOC/DI and object creation

Question

I'm building small web shop with asp.net mvc and Structuremap ioc/di. My Basket class uses session object for persistence, and I want use SM to create my basket object through IBasket interface. My basket implementation need HttpSessionStateBase (session state wrapper from mvc) in constructor, which is available inside Controller/Action. How do I register my IBasket implementation for SM?
This is my basket interface:

public interface IBasketService    {
    BasketContent GetBasket();
    void AddItem(Product productItem);
    void RemoveItem(Guid guid);
}

And SM registration:

ForRequestedType(typeof (IBasketService)).TheDefaultIsConcreteType(typeof (StoreBasketService));

But my StoreBasketService implementation has constructor:

public StoreBasketService(HttpSessionStateBase sessionState)

How do I provide HttpSessionStateBase object to SM, which is available only in controller?
This is my first use of SM IOC/DI, and cann't find solution/example in official documentation and web site ;)

Answer 1

If you absolutely have to have your StoreBasketService use the session, I'd be tempted to define an interface and wrapper around HttpSessionState instead of using HttpSessionStateBase so that you can register it with StructureMap as well.The wrapper would get the session state from the current context. Register the wrapper with StructureMap and then have your StoreBasketService take the interface as the argument to the constructor. Structure map should then know how to create an instance of the interface wrapper and inject it into your StoreBasketService class.

Using an interface and wrapper will allow you to mock the wrapper in your unit tests, muc in the same way HttpSessionStateBase allows mocking the actual session.

public interface IHttpSessionStateWrapper
{
    HttpSessionState GetSessionState();
}

public class HttpSessionStateWrapper : IHttpSessionStateWrapper
{
    public virtual HttpSessionState GetSessionState()
    {
       return HttpContext.Current.Session;
    }
}

ForRquestedType(typeof(IHttpSessionStateWrapper))
   .TheDefaultIsConcreteType(typeof(IHttpSessionStateWrapper));

---

public class StoreBasketService
{
   HttpSessionState session;
   public StoreBasketService( IHttpSessionstateWrapper wrapper )
   {
      session = wrapper.GetSessionState();
   }

   // basket implementation ...
}

However, you can have StructureMap actually store your basket in the session using .CacheBy(InstanceScope.HttpContext) when registering it. It may actually be better to have your StoreBasketService implement internal storage instead of storing things in the session -- then you lose the dependency on the session state entirely (from the perspective of your class) and your solution could be simpler. Your internal storage could be a Dictionary<Guid,Product> since this is how you access them via your interface.

See also:

http://www.lostechies.com/blogs/chad_myers/archive/2008/07/15/structuremap-basic-scenario-usage.aspx

http://www.lostechies.com/blogs/chad_myers/archive/2008/07/17/structuremap-medium-level-usage-scenarios.aspx

Answer 2

I just started with StructureMap, and I do not get the results you are describing. I performed a simple test using a simple class, configuring Structuremap to cacheby HttpContext, and from what I can see, CacheBy.HttpContext means within the same request you will get the same instance... not within the same Session

The constructor of my class, sets the date/time in a private field I have a button which gets 2 instances of MyClass with one second interval... It then display the time of both instances in a label.

Pressing the first time this button, object A and B are same instance, as their creation time is exactly the same, as expected.

Clicking the button a second time, you would expect the creation time to not have changed if instances would be cached in session... however, in my test I get a new creation time ...

Structuremap configuration:

         ObjectFactory.Initialize(x=>x.ForRequestedType<MyClass>(). CacheBy(InstanceScope.HttpContext));

Button clicked event of test page

     protected void btnTest_Click(object sender, EventArgs e)
    {
        MyClass c = ObjectFactory.GetInstance<MyClass>();
        System.Threading.Thread.Sleep(1000);
        MyClass b = ObjectFactory.GetInstance<MyClass>();



        lblResult.Text = String.Format("cache by httpcontext First:{0}  Second:{1}  session id {2} ", c.GetTimeCreated(), b.GetTimeCreated(),Session.SessionID);
    }

MyClass

public class MyClass
{
    private DateTime _timeCreated;
    public MyClass()
    {
        _timeCreated = DateTime.Now;
    }

    public string GetTimeCreated()
    {
        return _timeCreated.ToString("dd/MM/yyyy hh:mm:ss");
    }
}

Answer 3

You could also use one of the ObjectFactory.Inject methods to inject the HttpSessionStateBase into StructureMap. It would then invoke the constructor with the injected HttpSessionStateBase.

Answer 4

I just made my first attempt at creating an custom scope... build a small web application with it, and as far as I can see, it seems to work. This will cache the object inside the current user session and will return the same object as long as you remain inside the same session:

public class HttpSessionBuilder : CacheInterceptor
{
    private readonly string _prefix = Guid.NewGuid().ToString();

    protected override CacheInterceptor clone()
    {
        return this;
    }

    private string getKey(string instanceKey, Type pluginType)
    {
        return string.Format("{0}:{1}:{2}", pluginType.AssemblyQualifiedName, instanceKey, this._prefix);
    }

    public static bool HasContext()
    {
        return (HttpContext.Current.Session != null);
    }

    protected override bool isCached(string instanceKey, Type pluginType)
    {
        return HttpContext.Current.Session[this.getKey(instanceKey, pluginType)] != null;
    }

    protected override object retrieveFromCache(string instanceKey, Type pluginType)
    {
        return HttpContext.Current.Session[this.getKey(instanceKey, pluginType)];
    }

    protected override void storeInCache(string instanceKey, Type pluginType, object instance)
    {
        HttpContext.Current.Session.Add(this.getKey(instanceKey, pluginType), instance);
    }

}

You have to configure the ObjectFactory as follows in the global.asax Application_start

        ObjectFactory.Initialize(x=>
            x.ForRequestedType<MyClass>().InterceptConstructionWith(new HttpSessionBuilder()));

Answer 5

ForRequestedType<IBasketService>()
    .TheDefault.Is.OfConcreteType<StoreBasketService>()
    .WithCtorArg("sessionState").EqualTo(HttpContext.Current.Session);

?? does that work?