UnsupportedOperationException merge-saving many-to-many relation with hibernate and JPA

Question

I've set up a simple many-to-many relationship account : role with Hibernate but when I try to save an account in a unit test after it has had its role added I get an UnsupportedOperationException:

java.lang.UnsupportedOperationException     at java.util.AbstractList.remove(AbstractList.java:144)     at java.util.AbstractList$Itr.remove(AbstractList.java:360)     at java.util.AbstractList.removeRange(AbstractList.java:559)     at java.util.AbstractList.clear(AbstractList.java:217)     at org.hibernate.type.CollectionType.replaceElements(CollectionType.java:502)     at org.hibernate.type.CollectionType.replace(CollectionType.java:582)     at org.hibernate.type.TypeHelper.replace(TypeHelper.java:178)     at org.hibernate.event.def.DefaultMergeEventListener.copyValues(DefaultMergeEventListener.java:563)     at org.hibernate.event.def.DefaultMergeEventListener.entityIsPersistent(DefaultMergeEventListener.java:288)     at org.hibernate.event.def.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:261)     at org.hibernate.event.def.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:84)     at org.hibernate.impl.SessionImpl.fireMerge(SessionImpl.java:867)     at org.hibernate.impl.SessionImpl.merge(SessionImpl.java:851)     at org.hibernate.impl.SessionImpl.merge(SessionImpl.java:855)     at org.hibernate.ejb.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:686)     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)     at java.lang.reflect.Method.invoke(Method.java:597)     at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:240)     at $Proxy33.merge(Unknown Source)     at org.springframework.data.jpa.repository.support.SimpleJpaRepository.save(SimpleJpaRepository.java:360)     at ....JpaProvider.save(JpaProvider.java:161)     at ....DataModelTest.testAccountRole(DataModelTest.java:47)     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)     at java.lang.reflect.Method.invoke(Method.java:597)     at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)     at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)     at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)     at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)     at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)     at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)     at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:82)     at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)     at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:240)     at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)     at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)     at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)     at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)     at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)     at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)     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:236)     at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:180)     at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)     at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197) 

What's going wrong here? Is my entity setup faulty or is this a hibernate or JPA limitation forcing me to split apart my m:m relationship into 3 1:n relations modeling the m:n relationship table as well (which I wanted to avoid since it does not have any additional information). I've modeled other 1:n entities in my prototype and that seemed to work out nicely so far...

Here's my setup, any thoughts whether it might be faulty are appreciated.

Entities (simplified):

@Entity @Table(name="account") public class Account extends AbstractPersistable<Long> {      private static final long serialVersionUID = 627519641892468240L;      private String username;       @ManyToMany     @JoinTable( name = "account_roles",                  joinColumns = { @JoinColumn(name = "account_id")},                  inverseJoinColumns={@JoinColumn(name="role_id")})       private List<Role> roles;          public List<Role> getRoles() {         return roles;     }     public void setRoles(List<Role> roles) {         this.roles = roles;     }        @Entity     @Table(name="role")     public class Role extends AbstractPersistable<Long> {          private static final long serialVersionUID = 8127092070228048914L;          private String name;          @ManyToMany         @JoinTable( name = "account_roles",                        joinColumns={@JoinColumn(name="role_id")},                        inverseJoinColumns={@JoinColumn(name="account_id")})           private List<Account> accounts;           public List<Account> getAccounts() {             return accounts;         }          public void setAccounts(List<Account> accounts) {             this.accounts = accounts;         } 

Unit Test:

@TransactionConfiguration @ContextConfiguration({"classpath:dw-security-context-test.xml"}) @Transactional @RunWith(SpringJUnit4ClassRunner.class) public class DataModelTest {      @Inject     private AccountProvider accountProvider;          @Inject      private RoleProvider roleProvider;      @Before     public void mockAccountRolePermission(){         Account account = MockAccount.getSavedInstance(accountProvider);         Role role = MockRole.getSavedInstance(roleProvider);     }      @Test     public void testAccountRole(){               Account returnedAccount = accountProvider.findAll().get(0);         returnedAccount.setRoles(Arrays.asList(roleProvider.findAll().get(0)));         accountProvider.save(returnedAccount);      } } 

MockAccount (same for MockRole):

public class MockAccount {      public static Account getInstance(){         Account account = new Account();         account.setUsername(RandomData.rndStr("userName-", 5));         return account;     }      public static Account getSavedInstance(AccountProvider accountProvider){         Account account = getInstance();         accountProvider.save(account);         return account;     }  } 

And finally the Provider:

@Repository public class AccountProvider extends JpaProvider<Account, Long> {  } 

where JPAProvider just wraps a lot of JPARepository methods (at least as far as it is important in this case):

public abstract class JpaProvider<T extends Object, ID extends Serializable> implements JpaRepository<T, ID>, JpaSpecificationExecutor<T>, QueryDslPredicateExecutor<T> { ... } 

Any Ideas on why the save might be an UnsupportedOperation?

Answer 1

It is because of your

Arrays.asList(roleProvider.findAll().get(0)) 

This creates an unmodifiable list (in fact, a non-resizable list). Hibernate seems to expect a modifiable list. Try using this instead:

public void testAccountRole(){           Account returnedAccount = accountProvider.findAll().get(0);      List<Role> list = new ArrayList<Role>();     list.add(roleProvider.findAll().get(0));         returnedAccount.setRoles(list);        accountProvider.save(returnedAccount); } 

This solution won't explain why exactly you got the other exception (might be documented in the Hibernate docs), but it might be a valid workaround.

Answer 2

Hibernate's persistent variant of the Collection in question attempts to delegate to an abstract base class (PersistenceBag) that doesn't implement the add method.