EclipseLink：对MappedSuperclass的查询失败 [英] EclipseLink: Query to MappedSuperclass fails

问题描述

我的应用程序是一家销售鱼类，水族馆等的商店。我想根据销售数量获得所有商品中前10项的清单。我使用以下类：

My application is a store selling fishes, aquariums etc. I want to get a list of top 10 items among all the items based on sales count. I use the following class:

@MappedSuperclass
@NamedQueries({
    @NamedQuery(name="getTopItems",query="SELECT x FROM FishStoreItem x ORDER BY x.salescnt DESC, x.title DESC")
})
public abstract class FishStoreItem 
       extends DomainSuperClass implements Serializable {
......
}

问题出现在以下异常中：

Problem is in the following exception:

异常[EclipseLink-8034]（Eclipse
持久性服务 -
2.0.0.v20091127-r5931）：org。 eclipse.persistence.exceptions.JPQLException
异常描述：编译
查询时出错[getTopItems：SELECT x FROM
FishStoreItem x ORDER BY x.salescnt
DESC，x.title DESC] 。未知实体
类型[FishStoreItem]。

Exception [EclipseLink-8034] (Eclipse Persistence Services - 2.0.0.v20091127-r5931): org.eclipse.persistence.exceptions.JPQLException Exception Description: Error compiling the query [getTopItems: SELECT x FROM FishStoreItem x ORDER BY x.salescnt DESC, x.title DESC]. Unknown entity type [FishStoreItem].

相同的代码适用于Apache OpenJpa 2.0.0，但在EclipseLink版本中失败2.1.0,2.0.1,1.0。

Same code works fine with Apache OpenJpa 2.0.0, but fails with EclipseLink ver 2.1.0, 2.0.1, 1.0.

PS我已经找到了针对Hibernate的那个解决方案，但我想确定EclipseLink也是不可能的。

P.S. I've already found that solution for Hibernate, but I want to be sure that it is impossible for EclipseLink too.

推荐答案

映射的超类不是实体，不允许查询，持久化或关系到超类（参见映射超类）。

A mapped superclass is not an entity and does not allow querying, persisting, or relationships to the superclass (see Mapped Superclasses).

这在Apache OpenJPA 2.0用户指南中得到确认：

This is confirmed in Apache OpenJPA 2.0 User's Guide:

1.3。映射的超类

映射的超类是一个非实体
类，可以定义持久状态
和实体
子类的映射信息。映射的超类通常是抽象的
。与真正的
实体不同，您无法查询映射的
超类，将映射的超类
实例传递给任何 EntityManager 或
查询方法，或声明与映射的超类
目标的持久
关系。您使用 MappedSuperclass 标记
注释表示映射的超类
。

1.3. Mapped Superclass

A mapped superclass is a non-entity class that can define persistent state and mapping information for entity subclasses. Mapped superclasses are usually abstract. Unlike true entities, you cannot query a mapped superclass, pass a mapped superclass instance to any EntityManager or Query methods, or declare a persistent relation with a mapped superclass target. You denote a mapped superclass with the MappedSuperclass marker annotation.

...

注意

OpenJPA允许您查询映射的
超类。对映射的
超类的查询将返回所有匹配的
子类实例。 OpenJPA也
允许你声明与
映射的超类类型的关系;但是，你
无法查询这些关系。

OpenJPA allows you to query on mapped superclasses. A query on a mapped superclass will return all matching subclass instances. OpenJPA also allows you to declare relations to mapped superclass types; however, you cannot query across these relations.

因此，虽然OpenJPA允许您的查询，但这超出了JPA。不要指望它适用于任何JPA提供商。

So, while OpenJPA allows your query, this is beyond JPA. Don't expect it to work with any JPA provider.

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