Tomáš Müller ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=5b50823... ) *created* an issue Hibernate ORM ( https://hibernate.atlassian.net/browse/HHH?atlOrigin=eyJpIjoiYWE5ZGY3MDU5... ) / Bug ( https://hibernate.atlassian.net/browse/HHH-16825?atlOrigin=eyJpIjoiYWE5ZG... ) HHH-16825 ( https://hibernate.atlassian.net/browse/HHH-16825?atlOrigin=eyJpIjoiYWE5ZG... ) Cascading an entity with a composite key causes NullPointerException in AbstractClassJavaType.extractHashCode ( https://hibernate.atlassian.net/browse/HHH-16825?atlOrigin=eyJpIjoiYWE5ZG... ) Issue Type: Bug Affects Versions: 6.2.5 Assignee: Unassigned Attachments: Bottom.java, HashTest.java, Middle.java, Top.java Components: hibernate-core Created: 20/Jun/2023 06:14 AM Environment: Java 11 using MySQL 8 or Oracle 18 Priority: Major Reporter: Tomáš Müller ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=5b50823... ) I am in the process of migrating an application from Hibernate 4.3 to Hibernate 6.2. I have noticed something that works differently, causing a NullPointerException when there are two levels of one-to-many nesting with the bottom entity containing a composite id. That is when the composite id contains a relation that is being persisted together with the entity it refers to. Here is our example (simplified). Imagine having a Top entity that has a one-to-many relation to a Middle entity that has a one-to-many relation to a Bottom entity with a composite key (including id of the middle entity): Top entity: @Entity @Table(name = "top") public class Top { private UUID id; private String name; private Set<Middle> middles; @Id @GeneratedValue @Column(name = "id") public UUID getId() { return id; } public void setId(UUID id) { this.id = id; } @Column(name = "name") public String getName() { return name; } public void setName(String name) { this.name = name; } @OneToMany(mappedBy = "top", cascade = { CascadeType.ALL }) @Cache(usage = CacheConcurrencyStrategy.READ_WRITE) public Set<Middle> getMiddles() { return middles; } public void setMiddles(Set<Middle> middles) { this.middles = middles; } public void addMiddle(Middle middle) { if (middles == null) middles = new HashSet<Middle>(); middles.add(middle); } } Middle entity: @Entity @Table(name = "middle") public class Middle { private UUID id; private Top top; private Set<Bottom> bottoms; @Id @GeneratedValue @Column(name = "id") public UUID getId() { return id; } public void setId(UUID id) { this.id = id; } @ManyToOne(optional = false) @JoinColumn(name = "top_id", nullable = false) public Top getTop() { return top; } public void setTop(Top student) { this.top = student; } @OneToMany(mappedBy = "middle", cascade = {CascadeType.ALL}) @Cache(usage = CacheConcurrencyStrategy.READ_WRITE) public Set<Bottom> getBottoms() { return bottoms; } public void setBottoms(Set<Bottom> bottoms) { this.bottoms = bottoms; } public void addBottom(Bottom bottom) { if (bottoms == null) bottoms = new HashSet<Bottom>(); bottoms.add(bottom); } } Bottom entity: @Entity @Table(name = "bottom") public class Bottom { private Middle middle; private Integer type; private String note; @Id @ManyToOne(optional = false) @JoinColumn(name = "middle_id", nullable = false) public Middle getMiddle() { return middle; } public void setMiddle(Middle middle) { this.middle = middle; } @Id @Column(name = "type") public Integer getType() { return type; } public void setType(Integer type) { this.type = type; } @Column(name = "note", nullable = true, length = 2048) public String getNote() { return note; } public void setNote(String note) { this.note = note; } } Now, imagine that we want to update the top entity by adding a middle entity with a bottom entity to it. Like this: final Session hibSession1 = sf.openSession(); Transaction t1 = hibSession1.beginTransaction(); // Lookup a top entity Top top = hibSession1.createQuery("from Top where name = :name", Top.class).setParameter("name", "Top 1").uniqueResult(); System.out.println("Top: " + top.getId() + ", " + top.getName()); // Add one middle entity with a single bottom entity to the top entity Middle m1 = new Middle(); m1.setTop(top); top.addMiddle(m1); Bottom b1 = new Bottom(); b1.setMiddle(m1); m1.addBottom(b1); b1.setType(0); b1.setNote("Bottom 1"); // update the top entity hibSession1.merge(top); t1.commit(); hibSession1.close(); However, this fails with the following exception: java.lang.NullPointerException at org.hibernate.type.descriptor.java.AbstractClassJavaType.extractHashCode(AbstractClassJavaType.java:93) at org.hibernate.type.AbstractStandardBasicType.getHashCode(AbstractStandardBasicType.java:216) at org.hibernate.type.AbstractStandardBasicType.getHashCode(AbstractStandardBasicType.java:225) at org.hibernate.type.EntityType.getHashCode(EntityType.java:362) at org.hibernate.type.ComponentType.getHashCode(ComponentType.java:270) at org.hibernate.engine.spi.EntityKey.generateHashCode(EntityKey.java:60) at org.hibernate.engine.spi.EntityKey.<init>(EntityKey.java:53) at org.hibernate.internal.AbstractSharedSessionContract.generateEntityKey(AbstractSharedSessionContract.java:618) at org.hibernate.event.internal.DefaultMergeEventListener.entityState(DefaultMergeEventListener.java:189) at org.hibernate.event.internal.DefaultMergeEventListener.merge(DefaultMergeEventListener.java:147) at org.hibernate.event.internal.DefaultMergeEventListener.doMerge(DefaultMergeEventListener.java:142) at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:126) at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:138) at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:869) at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:840) at org.hibernate.engine.spi.CascadingActions$6.cascade(CascadingActions.java:253) at org.hibernate.engine.spi.CascadingActions$6.cascade(CascadingActions.java:243) at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:513) at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:434) at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:220) at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:547) at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:477) at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:437) at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:220) at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:153) at org.hibernate.event.internal.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:490) at org.hibernate.event.internal.DefaultMergeEventListener.entityIsTransient(DefaultMergeEventListener.java:239) at org.hibernate.event.internal.DefaultMergeEventListener.merge(DefaultMergeEventListener.java:152) at org.hibernate.event.internal.DefaultMergeEventListener.doMerge(DefaultMergeEventListener.java:142) at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:126) at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:138) at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:869) at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:840) at org.hibernate.engine.spi.CascadingActions$6.cascade(CascadingActions.java:253) at org.hibernate.engine.spi.CascadingActions$6.cascade(CascadingActions.java:243) at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:513) at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:434) at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:220) at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:547) at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:477) at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:437) at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:220) at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:153) at org.hibernate.event.internal.DefaultMergeEventListener.cascadeOnMerge(DefaultMergeEventListener.java:570) at org.hibernate.event.internal.DefaultMergeEventListener.entityIsPersistent(DefaultMergeEventListener.java:212) at org.hibernate.event.internal.DefaultMergeEventListener.merge(DefaultMergeEventListener.java:155) at org.hibernate.event.internal.DefaultMergeEventListener.doMerge(DefaultMergeEventListener.java:142) at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:126) at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:80) at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:127) at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:848) at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:834) at org.hibernate.bugs.hash.HashTest.testMerge(HashTest.java:52) Everything works fine when * the top entity is being created (with the middle and bottom entities) instead (calling persist instead of merge) * when the middle entities are persisted before (or instead of) merging the top entity * when the bottom entity has a generated id instead of a reference to the middle entity See the attached files for the whole test. 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