Filter constructor injection using Ninject

Question

I am trying to find a way to use Ninject to inject constructor dependencies into filters. I am finding many articles describing property injection which is now advised against,

Answer 1

There is a way to use constructor injection.

First you replace your attribute with an 'empty' one which you will just use as a marker

public class UserValidationAttribute : Attribute { }

Then you create a filter class as an IActionFilter.

public class UserValidationFilter : IActionFilter
{
    private readonly IRepository repository;

    public UserValidationFilter(IRepository repository)
    {
        this.repository = repository;
    }

    public void OnActionExecuting(ActionExecutingContext filterContext)
    {
        //do something
    }

    public void OnActionExecuted(ActionExecutedContext filterContext)
    {
        //do something
    }      
}

Then you can register it with something like

private static void RegisterServices(IKernel kernel)
{
    kernel.BindFilter<UserValidationFilter>(FilterScope.Action, 0)
        .WhenActionMethodHas<UserValidationAttribute>();
}

If your attribute itself has constructor parameters, you can pass them in like

kernel.BindFilter<UserValidationFilter>(FilterScope.Action, 0)
    .WhenActionMethodHas<UserValidationAttribute>();
    .WithConstructorArgumentFromActionAttribute<UserValidationAttribute>("myParameter", attr => attr.MyParameter);

The BindFilter syntax is part of Ninject.Web.Mvc.FilterBindingSyntax.

Answer 2

Assuming that the attribute is to be a part of the metadata, which means that it should be instantiated at the compile time, it is not possible to have a repository injected into an attribute by any ioc container. Containers operate in run time.

Answer 3

If you want to inject dependencies to a filer, you want to use property injection instead of constructor injection.

public class UserValidationAttribute : ActionFilterAttribute
{
    [Inject]
    private IRepository repository { get; set; }

    public UserValidationAttribute()
    {
    }
}

https://stackoverflow.com/a/7192754/296861