@Override
    public FieldUpdate getFieldUpdate(String fieldName) {
        String mapped = fieldMap.get(fieldName);
        if (mapped==null) {
            return docU.getFieldUpdate(fieldName);
        }
        // TODO how about structs here?
        return docU.getFieldUpdate(mapped);
    }
The field name map for schema mapping. The key is the field name that the docproc uses. 
The value is the actual name of the field in the document.
docproc/src/main/java/com/yahoo/docproc/proxy/ProxyDocumentUpdate.java