code: public static String getOrderByClause(Class<?> entityClass) {
          EntityTable table = getEntityTable(entityClass);
          if (table.getOrderByClause() != null) {
              return table.getOrderByClause();
          }
  
          List<EntityColumn> orderEntityColumns = new ArrayList<EntityColumn>();
          for (EntityColumn column : table.getEntityClassColumns()) {
              if (column.getOrderBy() != null) {
                  orderEntityColumns.add(column);
              }
          }
  
          Collections.sort(orderEntityColumns, new Comparator<EntityColumn>() {
              @Override
              public int compare(EntityColumn o1, EntityColumn o2) {
                  return o1.getOrderPriority() - o2.getOrderPriority();
              }
          });
  
          StringBuilder orderBy = new StringBuilder();
          for (EntityColumn column : orderEntityColumns) {
              if (orderBy.length() != 0) {
                  orderBy.append(",");
              }
              orderBy.append(column.getColumn()).append(" ").append(column.getOrderBy());
          }
          table.setOrderByClause(orderBy.toString());
          return table.getOrderByClause();
      }
docs: 获取默认的orderby语句
  
  @param entityClass
  @return