SharePoint 2010: Managed Metadata fields and the TaxonomyHiddenList

Notes to self and others:

When you create a Managed Metadata (aka Taxonomy) field in a SharePoint 2010 list or library, the field’s schema will look something like this:

<field id="{f6d2b908-4ed4-42f8-a491-e1177ed57596}" version="1" 
  rowordinal="0" colname="int3" name="Tags" staticname="Tags" 
  sourceid="{58701f50-42a0-4c3d-8fdd-fb6f3a798bc4}" 
  enforceuniquevalues="FALSE" required="FALSE" 
  showfield="Term1033" 
  webid="956683ae-54b0-46c4-8fe6-8e14309b6fcd" 
  list="{4c231f71-5ed3-49aa-a62f-3fbb9a900bd0}" 
  displayname="Tags" type="TaxonomyFieldType">

  <default>1;#A|6832dce7-bd84-4afc-8311-d5a1367dc282</default>
  <customization>
    <arrayofproperty>
      <property>
        <name>SspId</name>
        <value xmlns:p4="x-instance" p4:type="q1:string" 
xmlns:q1="x">5dc61acc-dfa4-41dd-aa85-dd71d054ab1f</value>
      </property>
      <property>
        <name>GroupId</name>
      </property>
...

(field definition and namespaces shortened for readability)

Some of the notable attributes are:

• Type – obvious
• WebId - The current list’s web
• SourceID - The current list’s id
• List - The ID of a “TaxonomyHiddenList” which resides in the current web, but as the name implies, is hidden.
• ShowField - the field in the TaxonomyHiddenList to display – looks like it’s locale enabled.
• The SspId property is also crucial – it is the TermStore ID used to access the TermSet – more on that in another blog post…

The TaxonomyHiddenList’s schema looks like most lists’ schema – HUGE.  Some of the interesting fields are:

• IdForTerm - in the case of the default value above (A) this field’s value matches the GUID 6832dce7-bd84-4afc-8311-d5a1367dc282
• IdForTermSet - this appears to be the term set id from the MM data store – I have another column in my list which is not tied to a centrally managed metadata store – its value shows as 0000….-00… etc.
• IdForTermStore – in my instance, this GUID is the same for both the managed and non-managed metadata field – matches the SspId above.