How to copy a Managed Metadata Column from one list to another?

Question

I have two lists that are using the same Managed Metadata column. I am attempting to copy this column when I create a new entry in one of the lists. My code looks like this:

        SPListItem li = site.RootWeb.Lists["UploadList"].AddItem();
        li["Title"] = workflowProperties.Item["Title"];
        li["TaxKeyword"] = (TaxonomyFieldValueCollection)workflowProperties.Item["TaxKeyword"]; 
        li.Update();

For some reason when I look at the new list item that is created it never has a value for the "TaxKeyword" column. I have tried not casting it to TaxonomyFieldValueCollection and it still does not work... Any suggestions on how to do this?

Answer 1

When setting the value of Taxonomy Fields always use TaxonomyField.SetFieldValue

var sourceValue = sourceItem["SColumn"] as TaxonomyFieldValueCollection; 
var targetField = targetList.Fields["TColumn"] as TaxonomyField; 
targetField.SetFieldValue(targetItem, sourceValue);
targetItem.Update(); 

Just setting targetItem["field"] doesn't update the hidden notes field or the hidden lookuplist

Answer 2

Use PopulateFromGuidValuePair method. Below is a snippet to set Managed Column value from another one.

TaxonomyFieldValueCollection sourceTaxVal = sourceItem["MMColumn"] as TaxonomyFieldValueCollection;
string taxVal = string.Empty;
foreach (TaxonomyFieldValue val in sourceTaxVal)
 {
    taxVal += val.Label + "|" + val.TermGuid + ";";
 }
 //taxVal = sourceItem["MMColumn"].ToString() //will also result in same value as above
 TaxonomyFieldValueCollection targetTaxVal = new TaxonomyFieldValueCollection(targetList.Fields["MMColumn"]);
 targetTaxVal.PopulateFromLabelGuidPairs(taxVal);
 targetItem["MMColumn"] = targetTaxVal;
 targetItem.Update();