Extraction of term custom properties from list item field of managed metadata type

The task was to extract custom properties from managed metadata field of list item. Custom properties can be stored in name value like collection for each term, which is very handy in many cases.

To extract custom properties from terms, first we need to get access to appropriate term store. To achieve this I wrote simple method. All you need to do is to cast your field to TaxonomyField. Then create TaxonomySession object, access term store associated with field and get apropriate term set associated with the field.

private TermSet getTermSet(SPListItem listItem, string fieldName)
{
    var taxField = listItem.Fields[fieldName] as TaxonomyField;
    var session = new TaxonomySession(listItem.Web.Site);
    var termStore = session.TermStores.FirstOrDefault(ts => ts.Id == taxField.SspId);
            
    if (termStore != null)
    {
        return termStore.GetTermSet(taxField.TermSetId);
    }

    return null;
}

To get guids of all terms stored in our listItem object, I wrote simple helper method to extract guids. It checks if field allows to store multiple values. If so, we can cast it's value to TaxonomyFieldValueCollection type and nicely get all term ids using linq expression. If we are dealing with single value field it is eounght to cast field value to TaxonomyFieldValue and grab it's term id.

private List<Guid> getTermIds(SPListItem listItem, string fieldName)
{
    var taxonomyField = listItem.Fields[fieldName] as TaxonomyField;
    if (taxonomyField.AllowMultipleValues)
    {
        var fieldValuesCollection = listItem[fieldName] as TaxonomyFieldValueCollection;
        return fieldValuesCollection.Select(x => new Guid(x.TermGuid)).ToList();
    }
    else
    {
        var fieldValue = listItem[fieldName] as TaxonomyFieldValue;
        return new List() { new Guid(fieldValue.TermGuid) };
    }
}

At the end, task is extremely simple. It is enough to get our term set which is connected to the field, get all guids of terms stored in list item get properties for each term.

public List<string> GetPropertyValues(SPListItem listItem, string fieldName, 
                                              List<string> customProperties)
{
    List<string> values = new List<string>();
    var termSet = getTermSet(listItem, fieldName);
    
    if(termSet!=null)
    {
      var termIds = getTermIds(listItem, fieldName);

      foreach (var termId in termIds)
      {
        var term = termSet.GetTerm(termId);
        customProperties.ForEach(x => values.Add(term.CustomProperties[x]));
      }
    }
    return values;
}

With two short helper methods, it turns out to be fairly simple task to achieve.