getSingleResult在hibernate的本地标量查询上返回代理 [英] getSingleResult returns proxy on native scalar query in hibernate

问题描述

我正在将我的JPA持久性提供者从EclipseLink 2.3切换到Hibernate 3.6.5.Final。问题出在本地查询。注意：这不是EclipseLink的问题。我试图从没有声明实体的表中获取标量值， String 。这里是代码：

  Query q = em.createNativeQuery（select foo where foo_id =？）; 
 q.setParameter（1，fooId）; 
 String description =（String）q.getSingleResult（）; 
  

使用Hibernate，我得到了一个 ClassCastException ，因为返回的对象实际上是一个代理对象。我不知道它是什么类型，但我知道它不是一个数组（ object.getClass（）。isArray（）是false），我知道它不是列表（ object instanceof List 是 false ）。

我缺少什么？

lockquote>

q.getSingleResult（）。getClass（）。getInterfaces（） return？

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类型 java.sql.Clob ， org.hibernate.engine.jdbc.WrappedClob 和 java.io.Serializable code>。 [...]我甚至没有意识到该列是一个clob，我很惊讶EclipseLink正在为我转换字符串






看起来EclipseLink很聪明，可以转换CLOB（它实际上是一个非常长的字符序列，就像 String ）到字符串，如果需要的话。有了Hibernate，必须明确地完成。我想这符合JPA规范。

I'm working on switching my JPA persistence provider from EclipseLink 2.3 to Hibernate 3.6.5.Final. The problem is with a native query. Note: this wasn't a problem with EclipseLink. I'm trying to obtain a scalar value, a String from a table that I don't have an Entity declared for. Here is the code:

Query q = em.createNativeQuery("select description from foo where foo_id = ?");
q.setParameter(1, fooId);
String description = (String)q.getSingleResult();

With Hibernate I get a ClassCastException because the object returned is actually a proxy object. I don't know what type it is, but I know it isn't an array (object.getClass().isArray() is false) and I know it isn't a List (object instanceof List is false).

What am I missing?

解决方案

Summarizing comments below the question:

What interfaces does q.getSingleResult().getClass().getInterfaces() return?

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It is of type java.sql.Clob, org.hibernate.engine.jdbc.WrappedClob, and java.io.Serializable. [...] I didn't even realize the column was a clob and I'm surprised EclipseLink was doing the conversion to String for me

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Looks like EclipseLink is smart enough to convert CLOB (which is actually a very long sequence of characters, just like String) to String if required. With Hibernate this must be done explicitly. I guess this complies to the JPA specification.

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