JPA TABLE_PER_CLASS继承：如何只选择SELECT超类条目？ [英] JPA TABLE_PER_CLASS inheritance: How to only SELECT superclass entries?

问题描述

我正在使用EclipseLink作为JPA提供程序。此外，我正在使用以下TABLE_PER_CLASS继承结构

I'm using EclipseLink as the JPA provider. Further I'm using the following TABLE_PER_CLASS inheritance structure

@javax.persistence.Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
@NamedQueries({
    @NamedQuery(name=Parent.QUERY_FIND_ALL, query="SELECT p FROM Parent p")
})
public class Parent {
        // the class code follows here
}

@javax.persistence.Entity 
@NamedQueries({
    @NamedQuery(name=Child.QUERY_FIND_ALL, query="SELECT c FROM Child c")
})

public class Child extends Parent {
        // the class code follows here
}

现在的问题是我只想接收父类的条目。但是使用命名查询SELECT p FROM Parent p，也会返回子表中的所有条目。

The problem now is that I only want to receive entries of the parent class. But with the named query "SELECT p FROM Parent p" also all entries from the child table are returned.

选择或查找代码如下：

public List findWithNamedQuery(String query) {
        return em.createNamedQuery(query).getResultList();
}

因此查询就是SELECT p FROM Parent p。

Thereby query is i.e. the "SELECT p FROM Parent p".

我怎样才能真正收到父条目而不是这个继承层次结构的所有条目？

How can I only receive really the parent entries and not all entries of this inheritacne hierarchy?

简而言之：怎么能我保留所有子条目不变，只返回父条目？

In short: How can I leave all child entries untouched, and return only the parent entries?

编辑1：

我正在使用EclipseLink 2.0.1，但每次我通过类型表达式尝试axtavt的解决方案时，都会出现以下错误：

EDIT 1:
I'm using EclipseLink 2.0.1, but every time I try axtavt's solution via the type expression, I get the following error:

"Invalid Type Expression on [my.domain.Parent].  The class does not have a descriptor, or a descriptor that does not use inheritance or uses a ClassExctractor for inheritance".

我已经更新到EclipseLink的最新稳定版本2.1.1，但它没有解决问题。

I've updated also to the latest stable version 2.1.1 of EclipseLink, but it doesn't resolve the issue.

推荐答案

Type表达式与TABLE_PER_CLASS继承结合在EclipseLink 2.1.1下不起作用，这似乎是是一个错误。

The Type expression in combination with TABLE_PER_CLASS inheritance doesn' t work under EclipseLink 2.1.1, this seems to be a bug.

另见 JPA 2.0：TYPE表达式异常

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