Update Existing Default Column Metadata Field in SharePoint Online

Question

I need to update an Managed Metadata field Default Value in over 100 libraries .When i first set the value i used the script as shown below .But when i am trying to set the script default value to new value.Its not working .Can some one please guide me with this

 $taxField = $list.Fields.GetByInternalNameOrTitle("MyField")
[Microsoft.SharePoint.Client.Taxonomy.TaxonomyField] $txField = [Microsoft.SharePoint.Client.ClientContext].GetMethod("CastTo").MakeGenericMethod([Microsoft.SharePoint.Client.Taxonomy.TaxonomyField]).Invoke($global:ctx, $taxField)
    $taxField .DefaultValue = "-1;#MydataField|29ca0c72-1fc4-435f-a09c-28585cb5eac9"
    $taxField .Update()
    $ctx.Load($taxField)
    $ctx.ExecuteQuery()

I noticed one more thing its that the actual value is getting updated but when you go to the column default value settings it shows the old value .But if i upload a new document it actually has the new value .Is there a way that i can fix this .Also only for the managed metadata field it shows this folder for all the other ones it shows the library as shown below

Answer 1

You need to validate the TaxonomyValue first, what this does is it will ensure it's entered in the TaxonomyHiddenList which will give you a real id instead of -1(which means there's no id yet). This TaxonomyHiddenList id is what's really usd to set the value, the others are more descriptive.

In CSOM it looks like this:

TaxonomyFieldValue taxValue = new TaxonomyFieldValue();
taxValue.WssId = -1;
taxValue.TermGuid = term.Id.ToString();
taxValue.Label = term.Name;
//get validate string
var validateValue = field.GetValidatedString(taxValue);
field.Context.ExecuteQueryRetry();

Notice we set -1 here as well, as we don't know the id yet.

validateValue.Value is what you need to assign to your defaultValue