private void updateClassToFieldsMap(String className, String field) {
    Map<String, Set<String>> map = DefaultQuery.getPdxClasstofieldsmap();
    Set<String> fields = map.get(className);
    if (fields == null) {
      fields = new HashSet<>();
      map.put(className, fields);
    }

    fields.add(field);
  }
reads field value from a PdxInstance

@return the value of the field from PdxInstance
geode-core/src/main/java/org/apache/geode/cache/query/internal/AttributeDescriptor.java