Modify existing lookup type column to managed metadata type

Question

We are in process of migrating one of our big website which is built in WSS 3.0 to SharePoint 2010 Standard version.

In the process we want to convert all lookup columns to managed metadata type. We have these lookup as site columns which have been used in different list/libraries.

We thought of two possible approaches:

1. Creating new column of Managed metadata column and copy value from lookup columns to this new column.
2. Converting type of existing Lookup column to Managed metadata, if everything works fine (minimal changes is required in our exiting code)

Now working on second approach above, we have performed following steps to convert existing lookup type column to managed metadata and conversion have been successful:

1. Add a hidden note field to as site column to support Managed metadata column (Managed metadata column is combination of two fields)
2. Change the”SchemaXml” of the existing lookup field to that of Managed metadata pointing newly added note field.
3. Push changes to List and update lookup field.
4. Bind Taxonomy terms set to converted field and push down changes to List.
5. Go to list using this lookup field and add note field created in step one to this list.
6. Step 1 to 5 convert lookup to managed metadata successfully.
7. Now update values in items corresponding this field.

From above method we have successfully converted lookup column type to managed metadata.

Now my question is that:

1. Is it right approach to do, because I didn’t find any reference on changing column type?
2. If this is right approach, does it guarantees that each functionality like search etc. will run smoothly on this column type and we will not run in trouble in future.
3. Is there any other approach to resolve the problem? Waiting for your responses and suggestions.

Thanks in advance.

Answer 1

I would not dare to go with your option 2, changing column type isn't generally supported.

I would consider a third option:

1. Create a temporary column
2. Move selection into temporary column
3. Delete choice field
4. Create Managed Metadata column with original name of choice column
5. Move infomation from temporary column into Managed Metadata column
6. Delete temporary column

Answer 2

I am quite sure that your approach will not work fully. I have not heard of an approach where a taxonomy column can be correctly added to a content type by XML only. Have you for example tested your approach with search functionality and metadata navigation on a document library?

I would go with your approach 1 (or Per's) and make sure to add the taxonomy columns via code to your content types. That way you make sure that all aspects of the taxonomy columns will work properly (at least in my personal experience).