An entity model with a key-many-to-one that uses joined inheritance always has to join the root table when querying a subclass, even if no attributes of the super types are used. This is unfortunately because the FK of the ToOneAttributeMapping uses the root table information for the mapping.

We should try to optimize this in org.hibernate.metamodel.mapping.internal.MappingModelCreationHelper#interpretToOneKeyDescriptor to be able to avoid always joining.

Note that there is code which build on the current behavior, but I added a TODO comment with this Jira key along with explanation of what needs to be done.