Filtering Content

A very common operation is filtering of lists. To simplify this there is a concept of filters. These are the filters available by default:

Filter Type	Description
AccessFilter	removes items not authorized by the user
CompositeFilter	is composed of other filters, removes items not authorized by all of these
NavigationFilter	is composed of a page, visible, published and access filter
CountFilter	skip and takes a number of items, needs to be reset after each use
DelegateFilter	encapsulates an action that does the filtering
DuplicateFilter	removes duplicates, needs to be reset after each use
InverseFilter	contains another filter which behavior is inversed
NullFilter	doesn't filter
PageFilter	allows only pages (not parts)
ParentFilter	removes anything not structured below a parent
PublishedFilter	removes unpublished and expired items
TypeFilter	removes items not deriving from a certain type
VisibleFilter	removes non-visible items
ZoneFilter	removes items not in a given zone

Examples

Example, filtering found items:

     private IEnumerable<ContentItem> FindRecentlyPublishedWithFinder()
     {
           var recentlyPublishedItems = N2.Find.Items
                .Where.Published.Gt(DateTime.Now.AddMonths(-1))
                .Filters(new AccessFilter())
                .Select();
           return recentlyPublishedItems;
     }

The GetChildren method without parameters uses AccessFilter. When filtering children remember to include an access filter. Example, filtering out child pages that are accessible:

     public ActionResult FilteringChildPages()
     {
           ViewData["childPages"] = CurrentPage.GetChildren(
                new CompositeFilter(
                      new AccessFilter(),
                      new PageFilter()));
           return View();
     }

The filter can also be invoked directly. Calling filter will remove entries from the list.

     public ActionResult FilteringLists()
     {
           var children = CurrentPage.GetChildren();
           var filter = new PublishedFilter();
           // filtering a list will remove entries from the list
           filter.Filter(children);
 
           return View();
     }

Without changing the list, it’s possible to call Pipe which returns the matching items.

     public ActionResult PipingEnumerations()
     {
           var children = CurrentPage.GetChildren();
           var filter = new PublishedFilter();
           // piping will return a filtered enumeration without changing the input
           var filteredChildren = filter.Pipe(children);
 
           return View();
     }