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A DD4T.net Implementation - Navigation (part 2)

In previous post, Navigation, I presented the foundation for deserializing the navigation XML into an object model. In this post, I'll continue presenting the NavigationFactory class and the integration with caching.

The NavigationFactory class is a singleton wired through dependency injection (such as Ninject) that uses caching to serve navigation object model for a given Publication.

[Inject]
public virtual ICacheWrapper CacheWrapper { get; set; }

public Navigation GetNavigation()
{
    string publicationUrl = UriHelper.GetPublicationUrl(HttpContext.Current);
    string key = GetKey(publicationUrl);

    Navigation navigation;
    object cacheElement;
    if (!CacheWrapper.TryGet(key, out cacheElement))
    {
        string virtualPath = publicationUrl + "system/navigation.xml";
        string filePath = HttpContext.Current.Request.MapPath(virtualPath);
        navigation = ParseXml<Navigation>(filePath);
        SetParent(navigation);

        if (navigation == null)
        {
            CacheWrapper.Insert(key, false, 1);
        }
        else
        {
            CacheWrapper.Insert(key, navigation, 60);
        }
    }
    else
    {
        navigation = cacheElement as Navigation;
    }

    return navigation;
}

Notice the following:
  • The returned navigation object model depends on the Publication identified for the current request. They method GetPublicationUrl from class UriHelper returns the first level folder of the URL path, which helps us identify the Publication;
  • Method ParseXml was presented in my previous post, mentioned above, and is in charge with deserializing the XML into an object model;
  • A null Navigation object is cached for one minute, just to make performance better, in case the navigation XML is somehow missing or not deserializeable; otherwise, the navigation object is cached for one hour;
  • For simplicity sake of this example, the code uses hard-coded values for cache times and the XML navigation path is "/system/navigation.xml" under the PublicationUrl;
  • Method SetParent is used to create the reference from child navigation item to its parent. Initially, the navigation XML contains only information about parent navigation item to its children, but in practice we also need the capability to traverse the navigation model upward;

private void SetParent(Navigation navigation)
{
    if (navigation == null)
    {
        return;
    }

    foreach (NavigationItem item in navigation.Items)
    {
        SetParent(item);
    }
}

private void SetParent(NavigationItem item)
{
    if (item == null || item.ChildItems == null)
    {
        return;
    }

    foreach (NavigationItem child in item.ChildItems)
    {
        child.ParentItem = item;
        SetParent(child);
    }
}

A useful method is GetNavigation(Navigation object) which gives us an array of NavigationItem objects situated under the 'root' Structure Group in the navigation model.

public NavigationItem[] GetNavigation(Navigation navigation)
{
    if (navigation == null || navigation.Items.IsNullOrEmpty())
    {
        return new NavigationItem[0];
    }

    NavigationItem[] childItems = navigation.Items[0].ChildItems;

    return childItems == null ? new NavigationItem[0] : childItems;
}

The code above is wired in Ninject using the following construct:

Bind<INavigationFactory>().To<NavigationFactory>().InSingletonScope();

Also, client code make use of the navigation using the following constructs:

INavigationFactory factory = DependencyResolver.Current.GetService<INavigationFactory>();
Navigation navigation = factory.GetNavigation();
NavigationItem[] items = factory.GetNavigation(navigation);


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