UnitOfWork.cs

public class UnitOfWork : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        var database = DependencyResolver.Current.GetService<ContactsContext>();

        database.BeginTransaction();
    }

    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        var database = DependencyResolver.Current.GetService<ContactsContext>();

        database.CloseTransaction(filterContext.Exception);
    }
}