Check Extended Field for Duplicates

Revo 2.6.2

I found this thread https://forums.modx.com/thread/101939/use-getobject-to-check-existing-data and was curious if it would work for an extended (ClassExtender) field ("screenName") to check if the same value already exists?

Not exactly, but this should do it:

Is this the entire snippet or part of the above snippet?

It would be a part of some other snippet where you'd respond to the duplicate name somehow (where the comment is).