Hibernate的HQl语句集锦

Hibernate---HQL

1、多表左连接：

String hql = "select count(*) " +
                        " from SysMsgUserLink a " +
                        " left join a.sysMsg b  " +
                        " left join a.sysRevUser c  " +
                        " left join a.sysSendUser d " +
                        " where ... ";

2、左连接加子查询：

String hql = "select count(*) " +
                        " from SysMsgUserLink a " +
                        " left join a.sysMsg b  " +
                        " left join a.sysRevUser c  " +
                        " left join a.sysSendUser d " +
                        " where ... " +
                        " and a.linkId in(" +
                        " select a.linkId " +
                        " from SysMsgUserLink a " +
                        " where ... ";

注意的关键点：
1、进行左连接的两张表在建立Model层时，就必须注解清楚其关联，否则会报 “无法识别该属性”的错误
2、其实跟sql是一样的用法，只是将数据库中的表名直接换成对象名称即可