Hi, This is an unusual mapping. My gut feeling is that it is not a valid mapping, but I don't see anything in the spec that would indicate it is invalid. Here is the mapping: @Entity public class Product { @Id @Column(name = "id") private int id; @OneToOne(cascade = CascadeType.ALL) @JoinColumn(name = "id", referencedColumnName = "productId", insertable = false, updatable = false) private ProductInfo productInfo; } @Entity public class ProductInfo{ @Id private int id; @Column(name = "productId", unique = true, updatable = false) private int productId; } Hibernate ignores referencedColumnName = "productId" and assumes that Product and ProductInfo share the same ID value. When the IDs are not the same, Product#productInfo will be null. It seem to me that the foreign key column should be ProductInfo#productId and should reference Product#id, but this doesn't make sense for a unidirectional one-to-one owned by Product. IMO, a bidirectional @OneToOne with ProductInfo owning the association would make more sense. A test case can be found at [1] Is the mapping invalid, or is this a bug in Hibernate? Thanks, Gail [1] https://github.com/gbadner/hibernate-test-case-templates/commit/d806d4ef5... _______________________________________________ hibernate-dev mailing list hibernate-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev

Hi Steve, I know that a bidirectional one-to-one association works properly with Product#productInfo on the "mappedBy" side, and ProductInfo#product on the owning side. With that mapping, ProductInfo#product is a ManyToOne that is a "logical" OneToOne. I agree that is the more natural way to map this association, but this use case is for a unidirectional one-to-one.

What I'm seeing in the debugger for this unidirectional one-to-one association, Product#productInfo, is that it is OneToOneType with: * #foreignKeyType == ForeignKeyDirection.TO_PARENT * #referenceToPrimaryKey == true Both of these seem wrong to me for a unidirectional one-to-one, but maybe I'm missing something. I should mention that, in this particular case, no foreign key is generated. Even so, ForeignKeyDirection.TO_PARENT, means that Hibernate assumes that the foreign key is defined in ProductInfo, not Product, doesn't it? If the foreign key were in ProductInfo, then it would make sense that #referenceToPrimaryKey == true. I want to make sure that I understand what should be expected behavior for this use case. Since Product#productInfo is a unidirectional one-to-one, I would have expected that OneToOneType would have: * #foreignKeyType == ForeignKeyDirection.FROM_PARENT (with foreign key column Product#id) * #referenceToPrimaryKey == false (since it references non-PK column ProductInfo#productId)

Also, Product#id will always be non-null, but that doesn't mean that there is a non-null association with ProductInfo. It seems that Hibernate should complain when an association cannot be found, unless the association is annotated with @NotFound(NotFoundAction.IGNORE). Does this sound right to you?

Thanks, Gail On Thu, Mar 8, 2018 at 11:22 AM, Steve Ebersole <steve(a)hibernate.org&gt; wrote: > For sure our model can handle this mapping, although maybe only from the > other side (that's generally the more natural mapping) - internally it's > called a "logical many-to-one". Personally I'd say there is nothing wrong > with the mapping per-se. > > > On Wed, Mar 7, 2018 at 4:36 PM Gail Badner <gbadner(a)redhat.com&gt; wrote: > >> Hi, >> >> This is an unusual mapping. My gut feeling is that it is not a valid >> mapping, but I don't see anything in the spec that would indicate it is >> invalid. >> >> Here is the mapping: >> >> @Entity >> public class Product { >> @Id >> @Column(name = "id") >> private int id; >> >> @OneToOne(cascade = CascadeType.ALL) >> @JoinColumn(name = "id", referencedColumnName = "productId", >> insertable = false, updatable = false) >> private ProductInfo productInfo; >> >> } >> >> @Entity >> public class ProductInfo{ >> @Id >> private int id; >> >> @Column(name = "productId", unique = true, updatable = false) >> private int productId; >> } >> >> Hibernate ignores referencedColumnName = "productId" and assumes that >> Product and ProductInfo share the same ID value. >> When the IDs are not the same, Product#productInfo will be null. >> >> It seem to me that the foreign key column should be >> ProductInfo#productId and should reference Product#id, but this >> doesn't make sense >> for a unidirectional one-to-one owned by Product. >> >> IMO, a bidirectional @OneToOne with ProductInfo owning the association >> would make more sense. >> >> A test case can be found at [1] >> >> Is the mapping invalid, or is this a bug in Hibernate? >> >> Thanks, >> Gail >> [1] >> https://github.com/gbadner/hibernate-test-case-templates/commit/d806d4ef5... >> _______________________________________________ >> hibernate-dev mailing list >> hibernate-dev(a)lists.jboss.org >> https://lists.jboss.org/mailman/listinfo/hibernate-dev >> >