Order of execution with multiple filters in web api

action-filter, asp.net, asp.net-web-api, asp.net-web-api2, c#

Solution

Some things to note here:

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

- Authorization Filters -> Action Filters -> Exception Filters

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; }
}

Problem

Original source