If using dynamic entities not defined by classes (as is the case when using EntityMode.MAP), there's no way to create a subquery. This is because javax.persistence.criteria.CriteriaQuery.subquery() takes an entity Class as an argument, and unlike javax.persistence.criteria.CriteriaQuery.from() there's no overloaded method to subquery by EntityType. This severely limits what can be done using entities mapped with EntityType for which there is no Java class.

Links to https://java.net/jira/browse/JPA_SPEC-71