Filter in Orchard

When working in Orchard, it’s always a good idea to look at the current codebase as an example.

The one I chose as a reference in creating my custom filter attribute is the Theme filter.

It is located in $\Orchard\Themes\ThemeFilter.cs inside the Orchard.Framework project.

You will notice that ThemeFilter is actually inherited from a class called FilterProvider.

namespace Orchard.Themes {
    public class ThemeFilter : FilterProvider, IActionFilter, IResultFilter {
        public void OnActionExecuting(ActionExecutingContext filterContext) {

Now lets have a look inside FilterProvider.

    public abstract class FilterProvider : IFilterProvider {
        void IFilterProvider.AddFilters(FilterInfo filterInfo) {
            AddFilters(filterInfo);
        }
 
        protected virtual void AddFilters(FilterInfo filterInfo) {
            if (this is IAuthorizationFilter)
                filterInfo.AuthorizationFilters.Add(this as IAuthorizationFilter);
            if (this is IActionFilter)
                filterInfo.ActionFilters.Add(this as IActionFilter);
            if (this is IResultFilter)
                filterInfo.ResultFilters.Add(this as IResultFilter);
            if (this is IExceptionFilter)
                filterInfo.ExceptionFilters.Add(this as IExceptionFilter);
        }
 
    }

Bingo, it turns out that if you create a class to inherit FilterProvider and some IActionFilter, they will be automatically applied to your actions as ActionFilter already.

Note that Orchard is clever enough to help you to inject your dependencies using Autofac by constructor injection too.

Attribute in Orchard

As you can see, when you created your custom filter, it actually automatically applied to all your actions.

What happanes if you only want to apply your filter in certain actions using attribute?

Its easy, just check the ThemeFilter and ThemeAttribute as an example:

1. create your own attribute
2. check whether the action contains this attribute inside your filter.
3. apply what you want if the attribute exists or do nothing if it’s not.