Set Managed Metadata field value with PowerShell and CSOM

In the previous post I demonstrated an easy way to migrate managed metadata term store objects to SharePoint Online with PowerShell.

Now when you have migrated the terms you might need to migrate some documents and set the metadata fields in SharePoint Online. In the same project I had to migrate around 600 documents to SPO including the metadata which had 6 managed metadata fields, 4 of them were multi-valued.

In this post I will share a powershell snipped to make TaxonomyFieldValueCollection and use it as value for field of type Managed Metadata.

I am showing this method because I got some mixed results when I used simple string as value. It is hard for me to explain why simply updating with taxonomy string did not worked in all cases.
For example, if the document was created in Office Web Apps I was unable to set the fields using a simple string. You can try using the string method and then cross-check  if everithing is set, because if you feed only metadata string(multi-valued) or just guid(for single-valued) you might not get any error, but the field will be left blank.

The challenge for me in the "TaxonomyFieldValueCollection" approach was to create TaxonomyField object instance, because I had to use the generic client context method CastTo and PowerShell don't work well with generic methods. This is why I decided it is worth sharing this example. You can see the code below.

Now a couple of words about the string that is used. In the example above I am setting multi-valued MM field with collection of two terms. The string is in format "<int>;#<label>|<guid> " with ;# delimiter between the terms. The integer is the item id of the term in the Taxonomy Hidden List, if you are using the term for first time or you do not know this id you can use the default value "-1".
The label part speaks for itself, this is the label of the term and the most important part is the guid of the term. If something is wrong with the format of the string you will see below error message.

---

"The given value for a taxonomy field was not formatted in the required <int>;#<label>|<guid> format."

---

This method is working every time for all items. I hope that this was helpful!