code: def subGraphHasField(self, parent_name, graph_name, field_name):
          
          subgraph = self._getSubGraph(parent_name, graph_name, True)
          return subgraph.hasField(field_name)
docs: Return true if subgraph with name graph_name with parent graph with
          name parent_name has field with name field_name.
          
          @param parent_name: Root Graph Name
          @param graph_name:  Subgraph Name
          @param field_name:  Field Name.
          @return:            Boolean