Re-use computed index field for multiple template fields

Question

Is there a way to re-use the code for a computed index field without just making derived classes? I would like to have an additional property in the config which tells the ComputeFieldValue method which template field to read from.

So my config patch would look like this:

<field 
  fieldName="mounting"
  templateFieldName="Mounting" <<new property here
  returnType="stringCollection">
    MyNamespace.MyComputedIndexField, MyAssembly
</field>

And my indexing class would be as follows:

public class MyComputedIndexField : AbstractComputedIndexField
{
    public string TemplateFieldName { get; set; }

    public override object ComputeFieldValue(IIndexable indexable)
    {
        Item item = indexable as SitecoreIndexableItem;
        if (item == null)
        {
            return null;
        }

        var values = item[TemplateFieldName]?.Split(new[] {";"}, StringSplitOptions.RemoveEmptyEntries); //readthe TemplateFieldName property here
        return values?.Select(v => v.Trim()).ToList();
    }
}

Obviously, I could just set the default fieldName property to the name of the template field, but that would constrain my field name to be named after the template field name.

Answer 1

Yes, you can extract custom parameters from XmlNode of your field configuration:

<field 
  fieldName="mounting"
  templateFieldName="Mounting" 
  returnType="stringCollection">
    MyNamespace.MyComputedIndexField, MyAssembly
</field>

using System.Xml;
using Sitecore.ContentSearch;
using Sitecore.ContentSearch.ComputedFields;
using Sitecore.Data.Fields;
using Sitecore.Data.Items;
using Sitecore.Xml;

public class MyComputedIndexField : IComputedIndexField 
{
    public string FieldName { get; set; }
    public string ReturnType { get; set; }
    public string TemplateFieldName { get; set; }

    public MyComputedIndexField(XmlNode configNode)
    {
        this.FieldName = XmlUtil.GetAttribute("fieldName", configNode);
        this.ReturnType = XmlUtil.GetAttribute("returnType", configNode);
        this.TemplateFieldName = XmlUtil.GetAttribute("templateFieldName", configNode);            
    }
        
    public virtual object ComputeFieldValue(IIndexable indexable)
    {
        Item item = indexable as SitecoreIndexableItem;
        if (item == null)
        {
            return null;
        }

        var values = item[TemplateFieldName]?.Split(new[] {";"}, StringSplitOptions.RemoveEmptyEntries); //readthe TemplateFieldName property here
        return values?.Select(v => v.Trim()).ToList();
    }
}

or with inheritance from AbstractComputedIndexField:

public class MyComputedIndexField : AbstractComputedIndexField
{
    public string TemplateFieldName { get; set; }

    public MyComputedIndexField(XmlNode configNode) : base(configNode)
    {
        this.TemplateFieldName = XmlUtil.GetAttribute("templateFieldName", configNode);            
    }
        
    public override object ComputeFieldValue(IIndexable indexable)
    {
        Item item = indexable as SitecoreIndexableItem;
        if (item == null)
        {
            return null;
        }

        var values = item[TemplateFieldName]?.Split(new[] {";"}, StringSplitOptions.RemoveEmptyEntries); //readthe TemplateFieldName property here
        return values?.Select(v => v.Trim()).ToList();
    }
}