code: public static <M extends AVObject> AVQuery<M> reverseQuery(Class<M> theParentClazz,
                                                               String relationKey, AVObject child) {
      AVQuery<M> query = new AVQuery<M>(Transformer.getSubClassName(theParentClazz), theParentClazz);
      query.whereEqualTo(relationKey, Utils.mapFromPointerObject(child));
      return query;
    }
docs: Create a query that can be used to query the parent objects in this relation.
  
  @param theParentClazz The parent subclass.
  @param relationKey The relation field key in parent
  @param child The child object.
  @return A AVQuery that restricts the results to parent objects in this relations.