Is there a way to add a property to all documents in a collection using RQL(Patch)?
Bulk-Insert is a possible solution, but it's required to write c# code, which is not a fast solution to achieve, specially in a matter that you need to manipulate your data and need to go back and forth for many times.
You can add a new field with Patching.
Can read about it here in RavenDB Book Under Patching Documents
i.e.
The following RQL will add the new field MyNewPropery
to all documents in the Categories collection:
from Categories
update {
this.MyNewPropery = "some content";
}