我将EclipseLink,并具有以下代码:JPA:为什么懒惰场装载如果EntityManager的关闭
public Temp getTemp() {
EntityManager em=emf.createEntityManager();
String queryString="SELECT a FROM Temp a";
EntityGraph<Temp> eg = em.createEntityGraph(Temp.class);
eg.addAttributeNodes("id");
//eg.addAttributeNodes("name");
Query query = em.createQuery(queryString);
query.setHint("javax.persistence.fetchgraph", eg);
List<Temp> items=query.getResultList();
em.close();// ENTITYMANAGER IS CLOSED
return items.get(0);
}
public void temp(){
Temp temp=getTemp();
System.out.println("id:"+temp.getId());
System.out.println("name:"+temp.getName());
}
正如你可以从代码中看到的,我们只加载ID。但是,当我们执行temp.getName()时,会再次执行SQL查询并加载必要的数据。为什么?我们确实关闭了实体经理。我期望得到temp.getName()的异常。
EDIT 1 一些研究,我发现了以下后 - 我如上所述是编织时的实际的行为是静态的(<property name="eclipselink.weaving" value="static"/>
+ de.empulse.eclipselink
织造插件)。然而,当编织是动态的(<property name="eclipselink.weaving" value="true"/>
)我得到异常:
java.lang.ClassNotFoundException: org.eclipse.persistence.internal.jpa.EntityManagerImpl not found by com.temp [57]
at org.apache.felix.framework.BundleWiringImpl.findClassOrResourceByDelegation(BundleWiringImpl.java:1574)
at org.apache.felix.framework.BundleWiringImpl.access$400(BundleWiringImpl.java:79)
at org.apache.felix.framework.BundleWiringImpl$BundleClassLoader.loadClass(BundleWiringImpl.java:2018)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at com.temp.Temp._persistence_checkFetched(Temp2.java)
at com.temp.Temp._persistence_get_name(Temp2.java)
at com.temp.Temp.getName(Temp.java:44)
所以问题搬到这里:Eclipselink: Difference between static and dynamic weaving
可能重复的[JPA EntityManager.detach()仍然加载懒惰关系](http://stackoverflow.com/questions/37562870/jpa-entitymanager-分离仍然加载懒惰关系) –