There are two techniques for inheritance which are commonly used in all Sitecore solutions; hierarchical inheritance and template inheritance. Sadly, Sitecore offers no straight forward out-of-the-box API methods for the two techniques. This post describes some simple and neat ways of implementing these techniques – and also shows of how to use extension methods in .net to extend Sitecore and ASP.NET classes. This post was partly inspired by the extension method contest at the Learn Sitecore website.
Template inheritance:
Template inheritance is an integral part of Sitecore which I hope that all of you Sitecore fans out there use extensively in your solutions. At Pentia, template inheritance is so vital that in practice, you will see no item.TemplateID == SomeID or item.TemplateKey = "sometemplate" in any of our code, just like you (hopefully) would never use MyObject.GetType().Name == "MyClass" in C#.
No, we always use the following extension method:
[sourcecode language="csharp"]
public static bool IsDerived(this Item item, ID templateId)
{
if (item == null || templateId.IsNull || item.Template == null)
return false;
TemplateItem templateItem = item.Database.Templates[templateId];
if (templateItem == null)
return false;
Template template = TemplateManager.GetTemplate(item);
return template != null && (template.ID == templateItem.ID || template.DescendsFrom(templateItem.ID));
}
[/sourcecode]
The method is used as item.IsDerived(“MyTemplate”) just as you would always do MyObject is MyClass in c#. Sadly, Sitecore offers no obvious way to do the same out-of-the-box….wait… oh yeah, you could naturally do Sitecore.Xml.Xsl.XslHelper.IsItemOfType()
Hierarchical inheritance:
While template inheritance is used to give all content of different types the same properties, hierarchical inheritance in Sitecore is slightly different. This is primarily used to allow a piece of content, a setting or a configuration to propagate down a branch in the tree – i.e. propogate down a number of content types which can be totally unrelated, but grouped together solely because of their content position. For example, this could be used to apply a given design theme to an entire subsite within you site. Using hierarchical inheritance, extension methods and Linq, this could be accomplished as such (pardon the train-wreck):
[sourcecode language="csharp"]
protected void Page_Load(object sender, EventArgs e) {
var theme = this.GetDataSourceItem().GetAncestorOrSelf().First(i => i.IsDerived("HasTheme")).Fields["Theme"].Value;
//…
}
[/sourcecode]
In this example there are – besides the IsDerived extension method described above – two very useful extension methods:
GetDataSourceItem extends the ASP.NET UserControl to provide easy access to the DataSource set on a sublayout and is implemented as follows:
[sourcecode language="csharp"]
public static Item GetDataSourceItem(this UserControl control)
{
Sublayout sublayout = GetSublayout(control);
if (sublayout == null)
return null;
string dataSourcePath = sublayout.DataSource;
return !String.IsNullOrEmpty(dataSourcePath) ? Context.Database.GetItem(dataSourcePath) : null;
}
[/sourcecode]
GetAncestorOfSelf extends item to return a list with the item itself and all its parents – and this is naturally where the key to hierarchical inheritance lies:
[sourcecode language="csharp"]
public static IEnumerable<Item> GetAncestorOrSelf(this Item item)
{
do {
yield return item;
item = item.Parent;
} while (item != null);
}
[/sourcecode]
I hope this post shows you how some simple extension methods can give you a lot of power in your solutions.
