c# - Order of execution with multiple filters in web api

Question

I am using latest web api.

I do annotate some controllers with 3 different filter attributes.

1 [Authorize]
2 [RessourceOwnerAttribute derived from AuthorizationFilterAttribute]
3 [InvalidModelStateAttribute derived from ActionFilterAttribute]

I can not be sure that the filters run in the order they are declared from top to down.

How do I define the order of execution in web api 2.1 ?

https://aspnetwebstack.codeplex.com/workitem/1065#

http://aspnet.uservoice.com/forums/147201-asp-net-web-api/suggestions/3346720-execution-order-of-mvc4-webapi-action-filters

Do I still have to fix that for myself ??

Answer 1

Some things to note here:

1. Filters get executed in the following order for an action: Globally Defined Filters -> Controller-specific Filters -> Action-specific Filters.
2. Authorization Filters -> Action Filters -> Exception Filters

3. Now the problem that you seem to mention is related to having multiple filters of the same kind (ex: Multiple ActionFilterAttribute decorated on a controller or an action. This is the case which would not guarantee the order as its based on reflection.). For this case, there is a way to do it in Web API using custom implementation of System.Web.Http.Filters.IFilterProvider. I have tried the following and did some testing to verify it. It seems to work fine. You can give it a try and see if it works as you expected.

   // Start clean by replacing with filter provider for global configuration.
   // For these globally added filters we need not do any ordering as filters are 
   // executed in the order they are added to the filter collection
   config.Services.Replace(typeof(IFilterProvider), new System.Web.Http.Filters.ConfigurationFilterProvider());
   
   // Custom action filter provider which does ordering
   config.Services.Add(typeof(IFilterProvider), new OrderedFilterProvider());
   

   ---

   public class OrderedFilterProvider : IFilterProvider
   {
       public IEnumerable<FilterInfo> GetFilters(HttpConfiguration configuration, HttpActionDescriptor actionDescriptor)
       {
           // controller-specific
           IEnumerable<FilterInfo> controllerSpecificFilters = OrderFilters(actionDescriptor.ControllerDescriptor.GetFilters(), FilterScope.Controller);
   
           // action-specific
           IEnumerable<FilterInfo> actionSpecificFilters = OrderFilters(actionDescriptor.GetFilters(), FilterScope.Action);
   
           return controllerSpecificFilters.Concat(actionSpecificFilters);
       }
   
       private IEnumerable<FilterInfo> OrderFilters(IEnumerable<IFilter> filters, FilterScope scope)
       {
           return filters.OfType<IOrderedFilter>()
                           .OrderBy(filter => filter.Order)
                           .Select(instance => new FilterInfo(instance, scope));
       }
   }
   

   ---

   //NOTE: Here I am creating base attributes which you would need to inherit from.
   public interface IOrderedFilter : IFilter
   {
       int Order { get; set; }
   }
   
   public class ActionFilterWithOrderAttribute : ActionFilterAttribute, IOrderedFilter
   {
       public int Order { get; set; }
   }
   
   public class AuthorizationFilterWithOrderAttribute : AuthorizationFilterAttribute, IOrderedFilter
   {
       public int Order { get; set; }
   }
   
   public class ExceptionFilterWithOrderAttribute : ExceptionFilterAttribute, IOrderedFilter
   {
       public int Order { get; set; }
   }