Hello Piotr Przybylski, as you can read from the @Convert annotation’s javadoc, JPA explicitly specifies that you should not apply converters to ID attributes. In fact, both Hibernate 5 and 6 ignore any conversion information applied to identifiers.

The error you’re getting is due to the stricter SQL function argument type validation that was introduced with Hibernate 6 and to the fact that YearMonth doesn’t map to a comparable SQL type.