Java Hibernate 标准：在没有映射关联的情况下连接表
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Hibernate criteria: Joining table without a mapped association
提问by Snukker
I'd like to use Hibernate's criteria api to formulate a particular query that joins two entities. Let's say I have two entities, Pet and Owner with a owner having many pets, but crucially that association is not mapped in the Java annotations or xml.
我想使用 Hibernate 的标准 api 来制定连接两个实体的特定查询。假设我有两个实体，Pet 和 Owner，一个拥有许多宠物的所有者，但至关重要的是，该关联并未映射到 Java 注释或 xml 中。
With hql, I could select owners that have a pet called 'fido' by specifying the join in the query (rather than adding a set of pets to the owner class).
使用 hql，我可以通过在查询中指定联接（而不是将一组宠物添加到所有者类）来选择拥有名为“fido”的宠物的所有者。
Can the same be done using hibernate criteria? If so how?
可以使用休眠标准来完成同样的事情吗？如果是这样怎么办？
Thanks, J
谢谢，J
采纳答案by David M
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.
我的理解是，如果您使用 HQL 执行此操作，您将使用过滤器创建笛卡尔连接，而不是内部连接。条件查询不支持这样做。
回答by tpdi
There's a SQLCriterion, which you can give arbitrary SQL, and add to your Criteria. In the SQLstring, the token {alias} "will be replaced by the alias of the root entity."
有一个SQLCriterion，您可以任意指定SQL，并添加到您的Criteria. 在SQL字符串中，标记 {alias} “将被根实体的别名替换。”
回答by Stefan Steinegger
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:
在 NHibernate 中，您可以使用定义为 DetachedCriteria 的子查询。不确定它在 Java 中是否相同，很可能是相同的：
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.
假设它是使用所有者的名字加入的。
回答by Pierre Pretorius
This is indeed possible with criteria:
这确实可以通过标准实现：
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.
更新：这实际上是执行子查询而不是连接，但它允许您在两个未定义休眠关系的实体上使用 Criteria。
回答by javasmith
Criterion ownerCriterion = Restrictions.sqlRestriction(SELECT ownerId FROM Owner WHERE ownerName ='bob');
Criteria criteria = getSession().createCriteria(Pet.class);
criteria.createCriteria("ownerId").add(ownerCriterion);
