Extending linq to sharepoint for Publishing HTML fields

Question

I've created a partial class to extend the default spmetal class to handle publishing html fields. As outlined here:

Extending the Object-Relational Mapping

Snippet from public partial class RelatedLinksItem : Item, ICustomMapping:

/// <summary>
/// Read only data is retrieved in this method for each extended SPMetal field
/// Used to Read - CRUD operation performed by SPMetal
/// </summary>
/// <param name="listItem"></param>
[CustomMapping(Columns = new string[] { CONTENT_FIELDtesthtml, CONTENT_FIELDLink })]
public void MapFrom(object listItem)
{
    SPListItem item = (SPListItem)listItem;

    // link
    this.ContentLink = item[CONTENT_FIELDLink] as LinkFieldValue;

    // html (does NOT work)
    HtmlField html = item[CONTENT_FIELDtesthtml] as HtmlField; // this returns null

    // html (does work)
    HtmlField html2 = (HtmlField)item.Fields.GetFieldByInternalName(CONTENT_FIELDtesthtml); // this returns object
    this.Contenttesthtml = html2;
    this.TestHtml = html2.GetFieldValueAsText(item[CONTENT_FIELDtesthtml]); // set property for rendering html
}

Snippet from "webpart":

    protected override void CreateChildControls()
    {
        using (OrganisationalPoliciesDataContext context = new OrganisationalPoliciesDataContext(SPContext.Current.Web.Url))
        {
            var results = from links in context.RelatedLinks
                          select links;

            foreach (var link in results)
            {
                // render link
                Controls.Add(new LiteralControl(string.Format("<p>Link: {0}</p>", link.ContentLink)));

                // render html
                Controls.Add(new LiteralControl(string.Format("<p>HTML: {0}</p>", link.TestHtml)));
            }
        }
    }

Two questions:

1. Why does HtmlField html = item[CONTENT_FIELDtesthtml] as HtmlField; return null, but the item.Fields.GetFieldByInternalName works correctly?
2. Is there a way to use the GetFieldValueAsText method from within the webpart or is the approach of storing the value in a custom property for accessing later acceptable?

Answer 1

1. You are casting the field value of item[CONTENT_FIELDtesthtml] to the type HtmlField. But HtmlField represents the type of the field and not the type of the field value. Thus HtmlField html will be assigned with null. Check this MSDN page for a reference of all publishing field types and value types.
   I am not sure what the field value type of a HtmlField is. Probably just string.
   So you should be safe to convert it to string:

   string html = Convert.ToString(item[CONTENT_FIELDtesthtml]);
   

2. I think storing the value in a property is the way to go. This way you achieve a separation of data layer and presentation layer.