Hibernate中使用Criteria接口的Projections类处理聚合结果

Projections类主要用于帮助Criteria接口完成数据的分组查询和统计功能

 

List cats = session.createCriteria(Cat. class )
               .setProjection(Projections.projectionList()
               .add(Projections.rowCount())
               .add(Projections.avg( " weight " ))
               .add(Projections.max( " weight " ))
               .add(Projections.min( " weight " ))
               .add(Projections.groupProperty( " color " ))
           ).addOrder(Order.asc( " color " )).list();

 以上代码相当于select color,count(*),avg(weight),max(weight),min(weight),min(weight) from cat group by color
                              order by color asc;