Hibernate:不能为OFFSET和LIMIT使用命名参数？

Question

我正在努力让以下NamedQuery工作:

@NamedQuery(name="MyEntity.findByUser", query="SELECT m FROM MyEntity m WHERE m.owner = :user OFFSET :offset LIMIT :limit")

问题是,这会导致Hibernate在服务器启动时使用以下堆栈跟踪进行爆炸:

[INFO] [talledLocalContainer] java.lang.NullPointerException
[INFO] [talledLocalContainer]   at org.hibernate.hql.ast.ParameterTranslationsImpl.getNamedParameterExpectedType(ParameterTranslationsImpl.java:63)
[INFO] [talledLocalContainer]   at org.hibernate.engine.query.HQLQueryPlan.buildParameterMetadata(HQLQueryPlan.java:296)
[INFO] [talledLocalContainer]   at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:97)
[INFO] [talledLocalContainer]   at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:56)
[INFO] [talledLocalContainer]   at org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:72)
[INFO] [talledLocalContainer]   at org.hibernate.impl.SessionFactoryImpl.checkNamedQueries(SessionFactoryImpl.java:400)
[INFO] [talledLocalContainer]   at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:351)
[INFO] [talledLocalContainer]   at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1291)
[INFO] [talledLocalContainer]   at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:713)
[INFO] [talledLocalContainer]   at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:121)
[INFO] [talledLocalContainer]   at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:83)
[INFO] [talledLocalContainer]   at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:60)
(...)

经过一些反复试验后,我发现用文字值(分别为0和10)替换":offset"和":limit"工作正常.是否有这样的原因,有没有办法让命名参数在我的查询中工作？

我已经看到一些其他示例使用定位参数来动态设置命名查询中的偏移量和限制值,但我宁愿不让我的代码退化为一堆难以理解的query.setParameter(1, "someValue");废话.命名参数应该摆脱那种垃圾代码.

Answer 1

Hibernate有一个特殊的API,用于在运行时指定这些概念.试试这个:

@NamedQuery(name="MyEntity.findByUser", 
    query="SELECT m FROM MyEntity m WHERE m.owner = :user") // don't put OFFSET or LIMIT here

...

entityManager.createNamedQuery("MyEntity.findByUser") 
.setFirstResult(20) // equivalent to OFFSET
.setMaxResults(5) // equivalent to LIMIT
.getResultList();

我想这样做的原因是数据库供应商在SQL查询中指定这些概念的方式和位置方面存在很大差异,因此选择一种格式而不是另一种格式是不合理的,并且很难尝试在它们之间进行转换.

通过这种方式,方言实现清楚地知道需要做什么,然后可以做到.