Hibernate 条件: 在没有映射关联的情况下连接表

我想使用 Hibernate 的标准 api 来制定一个连接两个实体的特定查询。假设我有两个实体，Pet 和 Owner，其中一个所有者拥有许多宠物，但关键是这种关联没有映射到 Java 注释或 xml 中。

使用 hql，我可以通过在查询中指定连接来选择拥有名为“ fido”的宠物的主人(而不是将一组宠物添加到主人类中)。

使用冬眠标准也可以做到这一点吗? 如果可以，怎么做？

谢谢, J

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最佳答案

My understanding is that if you do this using HQL, you are creating a Cartesian join with a filter, rather than an inner join. Criteria queries do not support doing this.

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There's a SQLCriterion, which you can give arbitrary SQL, and add to your Criteria. In the SQL string, the token {alias} "will be replaced by the alias of the root entity."

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In NHibernate you can use subqueries which are defined as DetachedCriteria. Not sure if it works the same in Java, most probably it is the same:

DetachedCriteria pets = DetachedCriteria.For<Pet>("pet")
.SetProjection(Projections.Property("pet.ownername"))
.Add(/* some filters */ );


session.CreateCriteria(typeof(Owner))
.Add(Subqueries.PropertyIn("name", pets);

Assumed that it is joined using the name of the owner.

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This is indeed possible with criteria:

DetachedCriteria ownerCriteria = DetachedCriteria.forClass(Owner.class);
ownerCriteria.setProjection(Property.forName("id"));
ownerCriteria.add(Restrictions.eq("ownername", "bob"));


Criteria criteria = getSession().createCriteria(Pet.class);
criteria.add(Property.forName("ownerId").in(ownerCriteria));

Update: This actually performs a sub-query instead of a join but it allows you to use Criteria on two entities that do not have a hibernate relationship defined.

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Criterion ownerCriterion = Restrictions.sqlRestriction(SELECT ownerId FROM   Owner WHERE ownerName ='bob');
Criteria criteria = getSession().createCriteria(Pet.class);
criteria.createCriteria("ownerId").add(ownerCriterion);

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