Hi! Currently it is not possible to add additional conditions on copying a source to a destination field.
But when using Nested documents there is often the case that objects in different hierarchies share the same field because they have the same type and name. Think of a common field name like 'name' or 'description'. So to use a copy field here the only option is to create unique fields for each hierarchy level, which can enlarge the schema very easily. What about adding the possibility that a copy field can have rules which can evaluate stored fields or doc values, and only if that condition evaluates to true copy it to the destination field. What do you think?
