为什么我在一个 Set 上使用 FetchType.LAZY 而在另一个 Set 上没有得到 LazyInitializationException？
Why am I getting a LazyInitializationException when using FetchType.LAZY on one Set, but not on the other?
我 运行 遇到了一个很奇怪的问题；似乎有些 Set 会延迟加载，但其他的不会，但底层 class 布局完全相同：
我有 4 个 classes，在 Spring-boot Hibernate 映射中：
这些是顶级class，事件：
@Entity
public class Event {
// Getters, setters, etc. are omitted.
@OneToMany(fetch = FetchType.LAZY, mappedBy = "event", cascade = CascadeType.ALL)
@ElementCollection(targetClass = Question.class)
private Set<Question> questions = new HashSet<>();
@OneToMany(fetch = FetchType.LAZY, mappedBy = "event", cascade = CascadeType.ALL)
@ElementCollection(targetClass = Participant.class)
private Set<Participant> participants = new HashSet<>();
@OneToMany(fetch = FetchType.LAZY, mappedBy = "event", cascade = CascadeType.ALL)
@ElementCollection(targetClass = Run.class)
private Set<Run> runs = new HashSet<>();
}
这些是链接到这个事件根节点的 3 个 classes class:
问题:
@Entity
public class Question {
// Getters, setters, etc. are omitted.
@ManyToOne(fetch = FetchType.LAZY)
private Event event;
}
参与者:
@Entity
public class Participant {
// Getters, setters, etc. are omitted.
@ManyToOne(fetch = FetchType.LAZY)
private Event event;
}
运行:
@Entity
public class Run {
// Getters, setters, etc. are omitted.
@ManyToOne(fetch = FetchType.LAZY)
private Event event;
}
当然，还有与 JPA 相关的空构造函数、其他构造函数、大量 Hibernate/JPA 标记和更多底层关系，但我相信这些在这里没有什么区别。将 Set<Run> 变量引入 Event class.
后开始出现问题
运行ning 程序，并创建一个 Event 类型的对象，添加事件，一切正常，但创建一个新的 运行 对象并尝试将其添加到 Event.runs 字段在 JUnit 测试中出现以下错误：
正在呼叫 event.getRuns().add(<a new 'Run' object>)：
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.ps.model.orm.Event.runs, could not initialize proxy - no Session
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:576)
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:215)
at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:555)
at org.hibernate.collection.internal.PersistentSet.add(PersistentSet.java:202)
at com.ps.HibernateTestApplicationTests.testRunCreation(HibernateTestApplicationTests.java:88)
at com.ps.HibernateTestApplicationTests.testAllTheThings(HibernateTestApplicationTests.java:37)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.junit.runners.model.FrameworkMethod.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:254)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:89)
at org.junit.runners.ParentRunner.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access[=15=]0(ParentRunner.java:58)
at org.junit.runners.ParentRunner.evaluate(ParentRunner.java:268)
at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:193)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
在这一点上，惰性实例化对我来说似乎是错误的。当我将 Event.runs 的 @OneToMany 标记的 FetchType.LAZY 更改为 FetchType.EAGER 时，程序按预期执行，但我不能我一辈子都弄不明白为什么 LAZY 在这里不起作用，而在其他 classes 却起作用，因为它们的结构几乎相同。
其他的工作，LAZY 和 EAGER，而这个没有，我真的没有看到映射或这里的任何东西，所以即使我现在只使用 EAGER 类型，而不是 LAZY，我知道这是不鼓励的，并且想知道是否有任何事情我可能已经看过了。
堆栈跟踪告诉您问题 -
could not initialize proxy - no Session
只需确保在 Session 仍然可用的事务中调用 event.getRuns().add(<a new 'Run' object>)。
如果使用 Spring 只需用 @Transactional
注释该方法
像这样
@Transactional
public void doSomething(){
Event event= // get Event from DB ;
event.getRuns.add(//new Run);
//some other stuff
}
我有同样的 problem.I 解决了这个问题，将以下代码添加到我的 web.xml file.I 希望它能帮助你 ;)
<filter>
<filter-name>SpringOpenEntityManagerInViewFilter</filter-name>
<filter-class>org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>SpringOpenEntityManagerInViewFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
我 运行 遇到了一个很奇怪的问题；似乎有些 Set 会延迟加载，但其他的不会，但底层 class 布局完全相同：
我有 4 个 classes，在 Spring-boot Hibernate 映射中：
这些是顶级class，事件：
@Entity
public class Event {
// Getters, setters, etc. are omitted.
@OneToMany(fetch = FetchType.LAZY, mappedBy = "event", cascade = CascadeType.ALL)
@ElementCollection(targetClass = Question.class)
private Set<Question> questions = new HashSet<>();
@OneToMany(fetch = FetchType.LAZY, mappedBy = "event", cascade = CascadeType.ALL)
@ElementCollection(targetClass = Participant.class)
private Set<Participant> participants = new HashSet<>();
@OneToMany(fetch = FetchType.LAZY, mappedBy = "event", cascade = CascadeType.ALL)
@ElementCollection(targetClass = Run.class)
private Set<Run> runs = new HashSet<>();
}
这些是链接到这个事件根节点的 3 个 classes class:
问题:
@Entity
public class Question {
// Getters, setters, etc. are omitted.
@ManyToOne(fetch = FetchType.LAZY)
private Event event;
}
参与者:
@Entity
public class Participant {
// Getters, setters, etc. are omitted.
@ManyToOne(fetch = FetchType.LAZY)
private Event event;
}
运行:
@Entity
public class Run {
// Getters, setters, etc. are omitted.
@ManyToOne(fetch = FetchType.LAZY)
private Event event;
}
当然，还有与 JPA 相关的空构造函数、其他构造函数、大量 Hibernate/JPA 标记和更多底层关系，但我相信这些在这里没有什么区别。将 Set<Run> 变量引入 Event class.
运行ning 程序，并创建一个 Event 类型的对象，添加事件，一切正常，但创建一个新的 运行 对象并尝试将其添加到 Event.runs 字段在 JUnit 测试中出现以下错误：
正在呼叫 event.getRuns().add(<a new 'Run' object>)：
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.ps.model.orm.Event.runs, could not initialize proxy - no Session
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:576)
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:215)
at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:555)
at org.hibernate.collection.internal.PersistentSet.add(PersistentSet.java:202)
at com.ps.HibernateTestApplicationTests.testRunCreation(HibernateTestApplicationTests.java:88)
at com.ps.HibernateTestApplicationTests.testAllTheThings(HibernateTestApplicationTests.java:37)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.junit.runners.model.FrameworkMethod.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:254)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:89)
at org.junit.runners.ParentRunner.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access[=15=]0(ParentRunner.java:58)
at org.junit.runners.ParentRunner.evaluate(ParentRunner.java:268)
at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:193)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
在这一点上，惰性实例化对我来说似乎是错误的。当我将 Event.runs 的 @OneToMany 标记的 FetchType.LAZY 更改为 FetchType.EAGER 时，程序按预期执行，但我不能我一辈子都弄不明白为什么 LAZY 在这里不起作用，而在其他 classes 却起作用，因为它们的结构几乎相同。
其他的工作，LAZY 和 EAGER，而这个没有，我真的没有看到映射或这里的任何东西，所以即使我现在只使用 EAGER 类型，而不是 LAZY，我知道这是不鼓励的，并且想知道是否有任何事情我可能已经看过了。
堆栈跟踪告诉您问题 -
could not initialize proxy - no Session
只需确保在 Session 仍然可用的事务中调用 event.getRuns().add(<a new 'Run' object>)。
如果使用 Spring 只需用 @Transactional
像这样
@Transactional
public void doSomething(){
Event event= // get Event from DB ;
event.getRuns.add(//new Run);
//some other stuff
}
我有同样的 problem.I 解决了这个问题，将以下代码添加到我的 web.xml file.I 希望它能帮助你 ;)
<filter>
<filter-name>SpringOpenEntityManagerInViewFilter</filter-name>
<filter-class>org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>SpringOpenEntityManagerInViewFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>