Problem with Setter injection with Structuremap

Question

I am creating an instance of a type scoped to HTTPContextScoped. I am trying to figure out how to inject this specific instance into a property of the same type into an attribute that I don't have control over.

I want to inject the specific instance of UnitOfWork into a property of IUnitOfWork type in an attribute (see code below)

Here is my ObjectFactory.Initialize() method of the part that I am referring to:

ObjectFactory.Initialize(x =>
{
    //...   
    //additional content
    //...

    x.For<IUnitOfWork>()
        .HttpContextScoped()
        .Use(context => new UnitOfWork(
            context.GetInstance<ISessionFactory>()));

    x.SetAllProperties(context =>
    {
        context.Matching(p => 
            p.DeclaringType == typeof(UnitOfWorkAttribute));
        context.OfType<IUnitOfWork>();
    });

Attribute Class:

public class UnitOfWorkAttribute : ActionFilterAttribute {

    public IUnitOfWork UnitOfWork { get; set; }

    public UnitOfWorkAttribute() {
        Order = 0;
    }

    public void OnActionExecuting(ActionExecutingContext filterContext) {
        UnitOfWork.Begin();
    }

    public void OnActionExecuted(ActionExecutedContext filterContext) {
        UnitOfWork.End();
    }
}

I was trying to follow one of Jeremy Miller's examples of using criteria to do so, but I am not doing something right.

Any thoughts of what I am doing incorrectly?

NOTE It does create the UnitOfWork instance as I use it else where, but I am specifically not correctly (or at all) injecting this attribute's property with that instance (or any for that matter).

You can't use dependency injection on attributes, because attributes are created and controlled by the .NET framework. If you show a little more of what you're doing (for instance your code for the UnitOfWorkAttribute), we might be able to come with an alternative solution. — Steven
– Steven, Commented May 4, 2011 at 13:20
@Steven: I have updated the UnitOfWorkAttibute Class with the full code. However, despite what you said according to this groups.google.com/group/structuremap-users/browse_thread/thread/… post (answered by Jeremy Miller) the poster is trying to accomplish nearly the same thing with instances he doesn't have access to and Jeremy appears to be stating it is possible. — pghtech
– pghtech, Commented May 4, 2011 at 13:37
As far as I see, the thread you linked to does not mention attributes. You want to inject a property in an attribute. — Steven
– Steven, Commented May 4, 2011 at 13:45

Steven · Accepted Answer · 2011-05-04 13:55:39Z

1

Try solving this problem by creating a factory for IUnitOfWork objects. Since the lifetime of unit of work instances must be controlled explicly (since you are doing Begin and End, controlling them yourself is much more logical, and adheres the principle of least surprise.

Here is an example of what you can do:

public interface IUnitOfWorkFactory
{
    IUnitOfWork NewUnitOfWork();
}

public class MyController : Controller
{
    private readonly IUnitOfWorkFactory factory;

    public MyController(IUnitOfWorkFactory factory)
    {
        this.factory = factory;
    }

    public void Operation()
    {
        using (var work = new this.factory.NewUnitOfWork())
        {
            work.Begin();

            // do some interesting stuff here.            

            work.End();
        }
    }
}

answered May 4, 2011 at 13:55

Steven

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1 Comment

pghtech Over a year ago

the use of the attribute which utilizes the OnActionExecuting and OnActionExecuted methods I can keep my code allot cleaner. In addition, since Structuremap is already creating an instance of IUnitOfWork, I would have no problem injecting it directly into the controller and not need to have the overhead of a Factory, also letting StructureMap handle the Life Time of the object.

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