How do I lazily-load a collection from a service method?

Question

I'm using Hibernate 5.1.3.Final with Spring 5.1. I'm having trouble loading a lazily-loaded collection. In my entity I have

@OneToMany(fetch = FetchType.LAZY)
@JoinTable(name = "sb_product_object", joinColumns = { @JoinColumn(name = "PRODUCT_ID") }, inverseJoinColumns = { @JoinColumn(name = "MY_OBJECT_ID") })
private List<MyObject> myObjects;

Then I have a service method where I load the objects

@Override
@Transactional
public List<MyObject> getMyObjectsByProduct(final String productId) 
{
    final Product product = productService.findById(productId);
    return product.getMyObjects();
}

but when I try and iterate over the objects,

        final List<MyObject> ret = m_myobjectsvc.getMyObjectsByProduct(productId);
        for (final MyObject assmt : ret)

I get this error ...

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: org.mainco.subco.ecom.domain.Product.myObjects, could not initialize proxy - no Session
    at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:582)
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:201)
    at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:561)
    at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:132)
    at org.hibernate.collection.internal.PersistentBag.iterator(PersistentBag.java:277)
    at org.mainco.subco.MyObject.mvc.MyObjectViewControllerIT.testSetDisplayTABIcon(MyObjectViewControllerIT.java:87)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.junit.runners.model.FrameworkMethod$1.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.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:73)
    at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:83)
    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.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:251)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.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:190)
    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:539)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:761)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:461)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:207)

How do I lazily load a collection from my service method?

Answer 1

In your situation, if you always iterate your collection, so i think you should avoid to use the lazy load because it causes N+1 problems and might impact to your performance.

Advanced solution: you should use "entity graph" in jpa 2.2, to load what you need.

For simply solution, just make sure collections is loaded by calling collections.size() in the same transaction.

No transaction anti pattern may be quite dangerous in my opinion. So avoid to use

Answer 2

Create session on enable Hibernate property enable_lazy_load_no_trans

<property name="hibernate.enable_lazy_load_no_trans" value="true"/>

https://vladmihalcea.com/the-hibernate-enable_lazy_load_no_trans-anti-pattern/