Referencing field names in a StoreFunc

[Rodrick]

Hi,
I would like to create a StoreFunc link MultiStorage that instead of 
referencing fields to be added to the output path by index, it references them 
by name (it would construct a map between names and indexes based on the schema 
of the data to be output). Is there a mechanism for a StoreFunc to access the 
schema of the data being stored? I thought overriding checkSchema would do 
this, but it does not seem to be called in all cases.
Thank you,Rodrick