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;