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HHH-18830 migration guide update 

Signed-off-by: Gavin King <gavin@hibernate.org>
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Gavin King 2024-11-11 10:15:05 +01:00
parent d5e829d26c
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migration-guide.adoc
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@ -410,6 +410,16 @@ Previously, `char` and `Character` fields were, by default, mapped to `char(1)`
However, MySQL treats a `char(1)` containing a single space as an empty string, resulting in broken behavior for some HQL and SQL functions.
Now, `varchar(1)` is used by default.
[[unowned-order-column]]
== `@OrderColumn` in unowned `@OneToMany` associations
In an unowned (`mappedBy`) one-to-many association, an `@OrderColumn` should, in principle, also be mapped by a field of the associated entity, and the value of the order column should be determined by the value of this field, not by the position in the list.
Previously, since version 4.1, https://hibernate.atlassian.net/issues/HHH-18830[Hibernate would issue superfluous SQL `UPDATE` statements] to set the value of the order column based on the state of the unowned collection.
This was incorrect according to the JPA specification, and inconsistent with the natural semantics of Hibernate.
In Hibernate 7, these SQL `UPDATE` statements only occur if the `@OrderColumn` is _not_ also mapped by a field of the entity.
[[cleanup]]
== Cleanup