Can Fetch be used as parameter of treat() for downcasting?

Dear hibernate community,

I am trying to use Fetch instead of Join as parameter of treat(), to avoid the problem that the duplicate join is generated by hibernate (as mentioned in How can I do a JOIN FETCH in criteria api). I am using hibernate-core “5.4.5.Final” and Spring Boot “2.1.8.RELEASE”.

Say a fetch is: “Fetch<Object, Object> fetch = root.fetch(“friends”, JoinType.LEFT);”.

If call “criteriaBuilder.treat((SetJoin<?, ?>) fetch, (Class) SpecialDroid.class)”, below exception will be thrown:

java.lang.UnsupportedOperationException: null
at java.util.AbstractCollection.add(AbstractCollection.java:262) ~[na:1.8.0_211]
at org.hibernate.query.criteria.internal.CriteriaBuilderImpl.treat(CriteriaBuilderImpl.java:1400) ~[hibernate-core-5.4.5.Final.jar:5.4.5.Final]
at org.hibernate.query.criteria.internal.CriteriaBuilderImpl.treat(CriteriaBuilderImpl.java:1125) ~[hibernate-core-5.4.5.Final.jar:5.4.5.Final]
at com.open_care.template_app.ignite_h2.controller.JPAQueryController.getFieldPredicates(JPAQueryController.java:57) ~[main/:na]
at com.open_care.template_app.ignite_h2.controller.JPAQueryController.getAllEmployeesFromRepository(JPAQueryController.java:32) ~[main/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_211]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_211]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_211]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_211]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
at

If call “criteriaBuilder.treat((Path) fetch, (Class) SpecialDroid.class)”, later entityManager.createQuery() will report error:

org.hibernate.hql.internal.ast.QuerySyntaxException: Invalid path: ‘generatedAlias1.secondaryFunction’ [select distinct human from com.open_care.template_app.ignite_h2.model.Human as human left join fetch human.friends as generatedAlias0 where treat(generatedAlias1 as com.open_care.template_app.ignite_h2.model.SpecialDroid).secondaryFunction like :param0]

Sounds that if hibernate can replace the ‘generatedAlias1’ in above query string with ‘generatedAlias0’, the problem can be solved.