Please find below the issue I have encountered during the migration from hibernate 5 to hibernante 6.1.7.

My sample project is using Lombok / Spring Data; its datamodel is composed of :

• Buckets having Lines

  @Getter
  @Setter
  @Entity
  @Table(name = "BUCKET")
  @SequenceGenerator(name = "SEQ_BUCKET_ID", allocationSize = 10, sequenceName = "SEQ_BUCKET_ID")
  @IdClass(PkBucket.class)
  public class Bucket {
  
      @Id
      @Column(name = "ID")
      @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_BUCKET_ID")
      private Long id;
  
      @OneToMany(cascade = CascadeType.ALL)
      @JoinColumn(name = "BUCKET_ID", referencedColumnName = "id", nullable = false)
      private List<Line> lines = new ArrayList<>();
  }

• Items having Lines

  @Getter
  @Setter
  @Entity
  @Table(name = "LINE")
  @SequenceGenerator(name = "SEQ_LINE_ID", allocationSize = 10, sequenceName = "SEQ_LINE_ID")
  @IdClass(PkLine.class)
  public class Line {
  
      @Id
      @Column(name = "ID")
      @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_LINE_ID")
      private Long id;
  
      @ManyToOne(targetEntity = Item.class)
      @JoinColumn(name = "ITEM_ID", referencedColumnName = "id", nullable = false)
      private Item item;
  }

• The Line class

  @Getter
  @Setter
  @Entity
  @Table(name = "ITEM")
  @SequenceGenerator(name = "SEQ_ITEM_ID", allocationSize = 10, sequenceName = "SEQ_ITEM_ID")
  @IdClass(PkItem.class)
  public class Item {
  
      @Id
      @Column(name = "ID")
      @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_ITEM_ID")
      private Long id;
  
      @OneToMany(mappedBy = "item", cascade = CascadeType.ALL, orphanRemoval = true)
      private List<Line> lines = new ArrayList<>();
  }

• The simplified Pk classes - they are all identical, as PkBucket here below

  @Getter
  @Setter
  public class PkBucket implements Serializable {
      private Long id;
  
      public PkBucket withId(Long id) {
          this.id = id;
          return this;
      }
  }

My test is creating and updating some data :

	@Test
	@Transactional
	public void buckets_items_lines() {
		// create some data
		Session session = entityManager.unwrap(Session.class);
		session.createNativeQuery("insert into ITEM (id) values (100)").executeUpdate();
		session.createNativeQuery("insert into ITEM (id) values (101)").executeUpdate();
		session.createNativeQuery("insert into BUCKET (id) values (200)").executeUpdate();
		session.createNativeQuery("insert into LINE (id, ITEM_ID, BUCKET_ID) values (300, 100, 200)").executeUpdate();

		// move line from item to other item
		Item item100 = itemRepository.findById(new PkItem().withId(100L)).get();
		final Item item101 = itemRepository.findById(new PkItem().withId(101L)).get();
		item100.getLines().forEach(line -> line.setItem(item101));
	}

The issue below occurs when tying to hydrate Item.lines:

Could not set value of type [java.lang.Long] : `com.example.demo.domain.issue2.PkBucket.id` (setter)
org.hibernate.PropertyAccessException: Could not set value of type [java.lang.Long] : `com.example.demo.domain.issue2.PkBucket.id` (setter)
	at app//org.hibernate.property.access.spi.SetterFieldImpl.set(SetterFieldImpl.java:81)
	at app//org.hibernate.metamodel.mapping.internal.AbstractEmbeddableMapping.setValues(AbstractEmbeddableMapping.java:103)

Few remarks:

• As you can see in the stack attached, the Line property id is accessed through PkBucket id instead of PkLine id.
• If I remove nullable = false from Bucket lines JoinColums the result is OK
• If I use unique Pk class the issue persists : IllegalArgumentException: Can not set java.lang.Long field com.example.demo.domain.issue2.Pk.id to com.example.demo.domain.issue2.Line
• If I force the Line class to extend the expected id class the result is OK but this is not nice 🙂

  ...
  @IdClass(PkLine.class)
  public class Line extends PkBucket {
  ...

I have attached the full log; if needed, I can also share my sample project.