UnsupportedOperationException when merging an existing Hibernate model object?

Question

After an upgrade from Hibernate 3 to 4, we're working through a few kinks that popped up along the way. One that has us particularly stumped is an UnsupportedOperationException, where an existing object is pulled from the database, tweaked, and merged.

The problem is that Hibernate appears to be adding an object to an AbstractList

This only seems to happen to one particular object type, when saved in our DAO, but as best as we can tell:

We're not using any sublist() or asList() methods that would cause an immutable instance to be created.
Examining the object that's being saved (which is enormous and has many children) I don't think that any of its children items are AbstractList types.

Here are the code snippets around the stack points:

HibernateDao.save():

@Transactional
public void save(T item) {
    try {
        getSessionFactory().getCurrentSession().merge(item);
    } catch (Exception ex) {
        LOGGER.debug("Unable to merge", ex);
        LOGGER.warn("Unable to merge item, saving instead. (Of type " + item.getClass() + ")");
        getSessionFactory().getCurrentSession().saveOrUpdate(item);
    }
}

Our User item, which is being saved, has a number of children items defined like so:

@OneToMany(cascade = CascadeType.ALL)
@LazyCollection(LazyCollectionOption.FALSE)
private Map<String, Project> associatedProjects = new HashMap<String, Project>();

The Project class has other similarly-annotated children, but everything has CascadeType.ALL, and LazyCollectionOption.FALSE defined.

Here is the (quite tall) stack trace:

Note that our code begins with com.company.application

06/04 18:15:45 DEBUG [Thread-19258] hibernate.HibernateDao.save- Unable to merge
java.lang.UnsupportedOperationException
        at java.util.AbstractList.add(AbstractList.java:148)
        at java.util.AbstractList.add(AbstractList.java:108)
        at org.hibernate.collection.internal.PersistentBag.add(PersistentBag.java:292)
        at org.hibernate.type.CollectionType.replaceElements(CollectionType.java:496)
        at org.hibernate.type.CollectionType.replace(CollectionType.java:563)
        at org.hibernate.type.AbstractType.replace(AbstractType.java:178)
        at org.hibernate.type.TypeHelper.replaceAssociations(TypeHelper.java:261)
        at org.hibernate.event.internal.DefaultMergeEventListener.copyValues(DefaultMergeEventListener.java:398)
        at org.hibernate.event.internal.DefaultMergeEventListener.entityIsTransient(DefaultMergeEventListener.java:221)
        at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:282)
        at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:151)
        at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:914)
        at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:896)
        at org.hibernate.engine.spi.CascadingAction$6.cascade(CascadingAction.java:288)
        at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:380)
        at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:323)
        at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:208)
        at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:409)
        at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:350)
        at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:326)
        at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:208)
        at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:165)
        at org.hibernate.event.internal.DefaultMergeEventListener.cascadeOnMerge(DefaultMergeEventListener.java:439)
        at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:308)
        at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:151)
        at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:914)
        at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:896)
        at org.hibernate.engine.spi.CascadingAction$6.cascade(CascadingAction.java:288)
        at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:380)
        at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:323)
        at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:208)
        at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:409)
        at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:350)
        at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:326)
        at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:208)
        at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:165)
        at org.hibernate.event.internal.DefaultMergeEventListener.cascadeOnMerge(DefaultMergeEventListener.java:439)
        at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:308)
        at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:151)
        at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:914)
        at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:896)
        at org.hibernate.engine.spi.CascadingAction$6.cascade(CascadingAction.java:288)
        at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:380)
        at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:323)
        at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:208)
        at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:409)
        at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:350)
        at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:326)
        at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:208)
        at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:165)
        at org.hibernate.event.internal.DefaultMergeEventListener.cascadeOnMerge(DefaultMergeEventListener.java:439)
        at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:308)
        at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:151)
        at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:76)
        at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:904)
        at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:888)
        at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:892)
        at com.company.hibernate.HibernateDao.save(HibernateDao.java:129)
        at sun.reflect.GeneratedMethodAccessor62.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:601)
        at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:318)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
        at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
        at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
        at $Proxy53.save(Unknown Source)
        at com.company.application.UserManager.save(UserManager.java:46)
        at sun.reflect.GeneratedMethodAccessor67.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:601)
        at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:318)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
        at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
        at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
        at $Proxy66.save(Unknown Source)
        at com.company.application.UserOperationController.saveUser(UserOperationController.java:533)

We're not sure where the AbstractList is coming from, or how we're responsible. Are there any potential pitfalls when working with Hibernate 4 (this issue is new since the upgrade) that could result in partially-unmodifiable objects? Or that would cause Hibernate to act in a way that results in it attempting to create unmodifiable instances of objects?

From the stacktrace, it sounds like the merge is being cascaded to other objects associated with the User. Do you have any collections mapped as a Bag type? — matt b
– matt b, Commented Jun 5, 2012 at 1:50
For me it looks like an error in hibernate, which would make it ugly to go around that issue. I think the only chance to get is, is to find out which child or grand child of item produces this error. For tests you can manually merge the children (and perhaps grand children) of item instead of letting cascade to that. — Johanna
– Johanna, Commented Jun 5, 2012 at 9:19
@mattb We definitely don't have any Bag types - only HashMap and ArrayList. Examining the object right before Hibernate merges it, it seems as though many of the ArrayList types were actually being wrapped by Hibernate in a PersistentBag. (But, underneath the bags were actual concrete ArrayList implementations, so I didn't see this to be a problem.) — Craig Otis
– Craig Otis, Commented Jun 5, 2012 at 10:37
@Johanna Thanks - I'll examine the object in the debugger again, and see if I can actually determine which child is causing issues. — Craig Otis
– Craig Otis, Commented Jun 5, 2012 at 10:38
you probably know this by now, but for future readers, whenever you persist a List without specifying the @Order, Hibernate will treat it as a bag. And the AbstractList comes from the backing list used in PersistentBag. — André Onuki
– André Onuki, Commented Apr 26, 2019 at 15:40

Chris Thompson · Accepted Answer · 2014-04-28 15:33:39Z

3

I ran into this same issue (with Sets not Lists) and it seems like Hibernate's Persistent variant of the collection in question attempts to delegate to an abstract base class that doesn't implement the add method. The solution I found was to set the data member to null, do a merge and then set the data member back to the new list that I wanted it to contain. The rather obvious downside is that I blow away all of the records even if I only want to add or remove one. The upside is that it actually works...

answered Apr 28, 2014 at 15:33

Chris Thompson

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Comments

RobertG · Accepted Answer · 2022-03-16 17:58:23Z

2

I had the same effect for recently - I had used java.util.Arrays#asList in my test case.

It was easy to miss, as the returned class is named ArrayList, but it was not java.util.ArrayList, but java.util.Arrays.ArrayList

answered Mar 16, 2022 at 17:58

RobertG

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Comments

Hemant · Accepted Answer · 2020-05-10 11:51:26Z

1

In this block of code:

@OneToMany(cascade = CascadeType.ALL)
@LazyCollection(LazyCollectionOption.FALSE)
private Map<String, Project> associatedProjects = new HashMap<String, Project>();

how about to add this.

@OneToMany(cascade = CascadeType.ALL)

*****@JoinColumn(name="")***** 

@LazyCollection(LazyCollectionOption.FALSE)
private Map<String, Project> associatedProjects = new HashMap<String, Project>();

edited May 10, 2020 at 11:51

Hemant

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answered Sep 10, 2013 at 9:17

Myo

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Comments

Nik Kashi · Accepted Answer · 2015-11-29 07:55:43Z

0

Use this transaction type:

@javax.transaction.Transactional(Transactional.TxType.REQUIRES_NEW)

answered Nov 29, 2015 at 7:55

Nik Kashi

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Tomas Kraus · Accepted Answer · 2025-01-02 13:40:12Z

0

I got the same issues while testing some Jakarta Persistence related code. I have entity with following mapping:

@ManyToMany(targetEntity = Type.class, fetch = FetchType.EAGER)
@JoinTable(name = "POKEMNON_TYPE",
           joinColumns = @JoinColumn(
                   name = "POKEMNON_ID",
                   referencedColumnName = "ID"
           ),
           inverseJoinColumns = @JoinColumn(
                   name = "TYPE_ID",
                   referencedColumnName = "ID"
           ))
public Collection<Type> types;

Which is spec 3.2 compliant. But Hibernate fails with the same stack trace. EclipseLink works fine with the same piece of code.

answered Jan 2 at 13:40

Tomas Kraus

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