code: public int execSelectCount(Class<? extends D6Model> modelClazz) {
  
      final D6CrudSelectHelper d6CrudSelectHelper = new D6CrudSelectHelper(modelClazz);
      final String sqlForSelectCount = d6CrudSelectHelper.getSQLForSelectCount();
  
      return execSelectCount(sqlForSelectCount);
    }
docs: Returns the total number of the lines of rows corresponding to the
  specified model class
  
  @param modelClazz
  @return true:DB operation success false:failure