blocks|key|1777741|text|无论您使用哪种JPA实现，只要使用entityManager.detach(object)就可以了，它现在是JPA2.0的一部分，也是JEE6的一部分。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1777742|entityMap^0|H|S|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

No matter which JPA implementation you use, Just use <code>entityManager.detach(object)</code> it's now in JPA 2.0 and part of JEE6.

blocks|key|1562317|text|如果您需要从EntityManager分离一个对象，并且您正在使用Hibernate作为底层ORM层，那么您可以访问Hibernate+Session对象，并使用Mauricio+Kanada上面提到的Session.evict(Object)方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1562318|public+void+detach(Object+entity)+{
++++org.hibernate.Session+session+=+(Session)+entityManager.getDelegate();
++++session.evict(entity);
}|code-block|syntax|javascript|1562319|当然，如果您切换到另一个ORM提供程序，这将会中断，但我认为这最好是尝试进行深度复制。|1562320|entityMap|0|LINK|mutability|MUTABLE|url|https://www.hibernate.org/hib_docs/v3/api/org/hibernate/Session.html|1|https://www.hibernate.org/hib_docs/v3/api/org/hibernate/Session.html#evict%2528java.lang.Object%2529^0|1M|H|0|2T|L|1|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]|$A|Y|B|Z|1|10]]|C|$]]|$1|D|3|E|5|F|7|11|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|12|8|@]|9|@]|C|$]]|$1|K|3|-4|5|6|7|13|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]|S|$5|N|O|P|C|$Q|T]]]]

If you need to detach an object from the EntityManager and you are using Hibernate as your underlying ORM layer you can get access to the <a href="https://www.hibernate.org/hib_docs/v3/api/org/hibernate/Session.html" rel="noreferrer">Hibernate Session</a> object and use the <a href="https://www.hibernate.org/hib_docs/v3/api/org/hibernate/Session.html#evict%28java.lang.Object%29" rel="noreferrer">Session.evict(Object)</a> method that Mauricio Kanada mentioned above.

<pre><code>public void detach(Object entity) {
 org.hibernate.Session session = (Session) entityManager.getDelegate();
 session.evict(entity);
}
</code></pre>

Of course this would break if you switched to another ORM provider but I think this is preferably to trying to make a deep copy.

blocks|key|1562425|text|如果使用EclipseLink，您还可以选择|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1562426|使用查询提示eclipselink.maintain-cache"="false+-所有返回的对象都将被分离。|1562427|使用EclipseLink+JpaEntityManager+copy()+API将对象复制到所需的深度。|1562428|entityMap^0|4|B|0|6|Y|0|2|B|E|G|V|6|0^^$0|@$1|2|3|4|5|6|7|L|8|@$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@]|E|$]]|$1|J|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|K|$]]

If using <code>EclipseLink</code> you also have the options,

Use the Query hint, <code>eclipselink.maintain-cache"="false</code> - all returned objects will be detached.

Use the <code>EclipseLink</code> <code>JpaEntityManager</code> <code>copy()</code> API to copy the object to the desired depth.

blocks|key|1777384|text|如果bean中没有太多的属性，您可以只创建一个新实例，并从持久化bean手动设置它的所有属性。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1777385|这可以作为复制构造函数来实现，例如：|1777386|public+Thing(Thing+oldBean)+{
++this.setPropertyOne(oldBean.getPropertyOne());
++//+and+so+on
}|code-block|syntax|javascript|1777387|然后：|1777388|Thing+newBean+=+new+Thing(oldBean);|1777389|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

If there aren't too many properties in the bean, you might just create a new instance and set all of its properties manually from the persisted bean.

This could be implemented as a copy constructor, for example:

<pre><code>public Thing(Thing oldBean) {
 this.setPropertyOne(oldBean.getPropertyOne());
 // and so on
}
</code></pre>

Then:

<pre><code>Thing newBean = new Thing(oldBean);
</code></pre>

blocks|key|1562213|text|这又快又脏，但您还可以序列化和反序列化对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1562214|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

this is quick and dirty, but you can also serialize and deserialize the object.

blocks|key|1777607|text|由于我使用的是SEAM和JPA1.0，并且我的系统具有需要记录所有字段更改的功能，因此如果需要记录的实体的相同字段，我创建了一个值对象或数据传输对象。新pojo的构造函数是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1777608|++++public+DocumentoAntigoDTO(Documento+documentoAtual)+{
++++Method[]+metodosDocumento+=+Documento.class.getMethods();
++++for(Method+metodo:metodosDocumento){
++++++++if(metodo.getName().contains("get")){
++++++++++++try+{
++++++++++++++++Object+resultadoInvoke+=+metodo.invoke(documentoAtual,null);
++++++++++++++++Method[]+metodosDocumentoAntigo+=+DocumentoAntigoDTO.class.getMethods();
++++++++++++++++for(Method+metodoAntigo+:+metodosDocumentoAntigo){
++++++++++++++++++++String+metodSetName+=+"set"+%2B+metodo.getName().substring(3);
++++++++++++++++++++if(metodoAntigo.getName().equals(metodSetName)){
++++++++++++++++++++++++metodoAntigo.invoke(this,+resultadoInvoke);
++++++++++++++++++++}
++++++++++++++++}
++++++++++++}+catch+(IllegalArgumentException+e)+{
++++++++++++++++e.printStackTrace();
++++++++++++}+catch+(IllegalAccessException+e)+{
++++++++++++++++e.printStackTrace();
++++++++++++}+catch+(InvocationTargetException+e)+{
++++++++++++++++e.printStackTrace();
++++++++++++}
++++++++}
++++}
}|code-block|syntax|javascript|1777609|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Since I am using SEAM and JPA 1.0 and my system has a fuctinality that needs to log all fields changes, i have created an value object or data transfer object if same fields of the entity that needs to be logged. The constructor of the new pojo is:

<pre><code> public DocumentoAntigoDTO(Documento documentoAtual) {
 Method[] metodosDocumento = Documento.class.getMethods();
 for(Method metodo:metodosDocumento){
 if(metodo.getName().contains("get")){
 try {
 Object resultadoInvoke = metodo.invoke(documentoAtual,null);
 Method[] metodosDocumentoAntigo = DocumentoAntigoDTO.class.getMethods();
 for(Method metodoAntigo : metodosDocumentoAntigo){
 String metodSetName = "set" + metodo.getName().substring(3);
 if(metodoAntigo.getName().equals(metodSetName)){
 metodoAntigo.invoke(this, resultadoInvoke);
 }
 }
 } catch (IllegalArgumentException e) {
 e.printStackTrace();
 } catch (IllegalAccessException e) {
 e.printStackTrace();
 } catch (InvocationTargetException e) {
 e.printStackTrace();
 }
 }
 }
}
</code></pre>

blocks|key|1562571|text|在JPA1.0(使用EclipseLink测试)中，您可以在事务之外检索实体。例如，使用容器管理的事务，您可以执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1562572|public+MyEntity+myMethod(long+id)+{
++++final+MyEntity+myEntity+=+retrieve(id);
++++//+myEntity+is+detached+here
}

@TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED)
public+MyEntity+retrieve(long+id)+{
++++return+entityManager.find(MyEntity.class,+id);
}|code-block|syntax|javascript|1562573|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

In JPA 1.0 (tested using EclipseLink) you could retrieve the entity outside of a transaction. For example, with container managed transactions you could do:

<pre><code>public MyEntity myMethod(long id) {
 final MyEntity myEntity = retrieve(id);
 // myEntity is detached here
}

@TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED)
public MyEntity retrieve(long id) {
 return entityManager.find(MyEntity.class, id);
}
</code></pre>

blocks|key|1777825|text|我创建了一个DTO对象，它扩展了持久实体对象，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1777826|class+MyEntity
{
+++public+static+class+MyEntityDO+extends+MyEntity+{}

}|code-block|syntax|javascript|1777827|最后，标量查询将检索所需的非托管属性：|1777828|(Hibernate)+select+p.id,+p.name+from+MyEntity+P
(JPA)+++++++select+new+MyEntity(p.id,+p.name)+from+myEntity+P|1777829|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Do deal with a similar case I have created a DTO object that extends the persistent entity object as follows:

<pre><code>class MyEntity
{
 public static class MyEntityDO extends MyEntity {}

}
</code></pre>

Finally, an scalar query will retrieve the desired non managed attributes:

<pre><code>(Hibernate) select p.id, p.name from MyEntity P
(JPA) select new MyEntity(p.id, p.name) from myEntity P
</code></pre>

blocks|key|1562493|text|如果您之所以来到这里，是因为您实际上想要跨越远程边界传递一个实体，那么您只需放入一些代码来欺骗hibernazi即可。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1562494|for(RssItem+i+:+result.getChannel().getItem()){
}|code-block|syntax|javascript|1562495|Cloneable无法工作，因为它实际上复制了PersistantBag。|1562496|并且忘记使用可序列化和字节数组流以及管道流。创建线程来避免死锁会扼杀整个概念。|1562497|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If you get here because you actually want to pass an entity across a remote boundary then you just put some code in to fool the hibernazi.

<pre><code>for(RssItem i : result.getChannel().getItem()){
}
</code></pre>

Cloneable wont work because it actually copies the PersistantBag across. 

And forget about using serializable and bytearray streams and piped streams. creating threads to avoid deadlocks kills the entire concept.

blocks|key|1562685|text|我认为有一种方法可以将单个实体从EntityManager中逐出，方法是调用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1562686|EntityManagerFactory+emf;
emf.getCache().evict(Entity);|code-block|syntax|javascript|1562687|这将从缓存中删除特定的实体。|1562688|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I think there is a way to evict a single entity from EntityManager by calling this

<pre><code>EntityManagerFactory emf;
emf.getCache().evict(Entity);
</code></pre>

This will remove particular entity from cache.

blocks|key|1777900|text|我正在使用entityManager.detach(returnObject)；它对我很有效。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1777901|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Im using entityManager.detach(returnObject);
which worked for me.

blocks|key|1777512|text|我认为如果实体的主键没有改变，你也可以使用方法EntityManager.refresh(Object+o)。此方法将恢复实体的原始状态。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1777513|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I think you can also use method EntityManager.refresh(Object o) if primary key of the entity has not been changed. This method will restore original state of the entity.

What would be the easiest way to detach a specific JPA Entity Bean that was acquired through an EntityManager. Alternatively, could I have a query return detached objects in the first place so they would essentially act as 'read only'?

The reason why I want to do this is becuase I want to modify the data within the bean - with in my application only, but not ever have it persisted to the database. In my program, I eventually have to call flush() on the EntityManager, which would persist all changes from attached entities to the underyling database, but I want to exclude specific objects.

Detach an entity from JPA/EJB3 persistence context

数据库

容器

分离通过EntityManager获取的特定JPA实体Bean的最简单方法是什么？或者，我可以让一个查询在第一个地方返回分离的对象，以便它们本质上是“只读”的吗？之所以要这样做，是因为我想修改bean中的数据--只在我的应用程序中使用，而不是将其持久化到数据库中。在我的程序中，我最终必须在EntityManager上调用flush()，它将持久化从附加实体到底层数据库的所有更改，但是我想排除特定的

问从JPA/EJB3持久性上下文中分离实体
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