ComputedIndexField with extra attributes

ComputedIndexField attributes

In the code that populates my ComputedIndexField I needed a reference to a Sitecore item. I needed to know a "context" item from which I had t retrieve data. Apparently you can extend Sitecore to do this (off course).

My configuration look like this (in a separate config file):

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
 <sitecore>
  <contentSearch>
   <configuration type="Sitecore.ContentSearch.LuceneProvider.LuceneSearchConfiguration, 
                                  Sitecore.ContentSearch.LuceneProvider">
    <indexes hint="list:AddIndex">
     <index id="MyIndexName" 
         type="Sitecore.ContentSearch.LuceneProvider.LuceneIndex,Sitecore.ContentSearch.LuceneProvider">
      <configuration type="Demo.Search.LuceneIndexConfiguration, Demo">
       <documentOptions type="Sitecore.ContentSearch.LuceneProvider.LuceneDocumentBuilderOptions">
        <ProcessDependencies>true</ProcessDependencies>
       </documentOptions>
       <fields hint="raw:AddComputedIndexField">
        <field fieldName="DemoContent" label="{1174978C-47CA-405D-13FE-4C808F3A85E7}">
          Demo.Search.DemoField, Demo
        </field>
       </fields>
      </configuration>
     </index>
    </indexes>
   </configuration>
  </contentSearch>
 </sitecore>
</configuration>

 So I added an attribute "label" in my field definition. Now we need a custom IndexConfiguration, and we will start with the one from Sitecore (reverse engineer that one and you will see we only added a few lines).

Custom IndexConfigration

public class LuceneIndexConfiguration : Sitecore.ContentSearch.LuceneProvider.LuceneIndexConfiguration
{
  public override void AddComputedIndexField(XmlNode configNode)
  {
    Assert.ArgumentNotNull(configNode, "configNode");
    string fieldName = XmlUtil.GetAttribute("fieldName", configNode, true);
    string type = XmlUtil.GetValue(configNode);            
    if (string.IsNullOrEmpty(fieldName) || string.IsNullOrEmpty(type))
    {
      throw new InvalidOperationException("Could not parse computed index field entry: " + configNode.OuterXml);
    }
    var field = ReflectionUtil.CreateObject(type) as IComputedIndexField;

    // here starts custom code
    var constructableField = field as IConstructable;
    if (constructableField != null)
    {
     constructableField.Constructed(configNode);
    }
    // end custom code

    if (field != null)
    {
      field.FieldName = fieldName.ToLowerInvariant();
      DocumentOptions.ComputedIndexFields.Add(field);
    }
  }
}

The extra stuff is based on the IConstuctable interface. This allows you to created a Constructed method that can read your xml node. You can use your own interfaces as well surely, but this one is already in the box..

And then we adapt the code for our ComputedIndexField:

IConstructable

public class DemoField : Sitecore.ContentSearch.ComputedFields.IComputedIndexField, IConstructable
{
  private Item MyItem { get; set; }

  public void Constructed(XmlNode configuration)
  {
    var label = XmlUtil.GetAttribute("label", configuration, true);
    if (string.IsNullOrEmpty(label))
    {
      ....
      return;
    }

    Guid id;
    if (Guid.TryParse(label, out id))
    {
      MyItem = Factory.GetDatabase("master").GetItem(new ID(id));
    }
  }

  public object ComputeFieldValue(IIndexable indexable)
  {
    ...
  }
}

We implement the Constructed method and read the xml node. The GetAttribute function is very useful here. We set the MyItem that will be used later on in the ComputedFieldValue function called by the crawler.