Multi-level subquery with JPA CriteriaBuilder - jpa

Question

I have the following JPA entities
#Entity
#Table(name="application_user")
public class ApplicationUser {
#Id
#Column(name="user_id")
private String userid;
#Column(name="last_write_time")
private Instant lastWrite;
//other fields omitted
}
#Entity
#Table(name="demographic")
public class Demographic {
#Id
#Column(name="user_id")
private String userid;
//primary key is a foreign key link
#OneToOne
#PrimaryKeyJoinColumn(name="user_id", referencedColumnName="user_id")
private ApplicationUser user;
//other fields omitted
}
My goal is to retrieve all of the Demographics that contains users where the last write time is the max value in the column. I pretty much want to write the following SQL using the JPA CriteriaBUilder
select * from demographic where
userid in (
select userid from application_user where
last_write in (
select max(last_write) from application_user
)
)
I tried writing the following CriteriaBuilder Code to accomplish this goal and it compiles successfully. Note I am using the generated Metamodel classes.
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Demographic> c = cb.createQuery(Demographic.class);
Root<Demographic> root = c.from(Demographic.class);
root.fetch(Demographic_.user, JoinType.INNER);
Subquery<Instant> sqLatestUsers = c.subquery(Instant.class);
Root<ApplicationUser> subRootLatestUsers = sqLatestUsers.from(ApplicationUser.class);
sqLatestUsers.select(cb.greatest(subRootLatestUsers.<Instant>get(ApplicationUser_.LAST_WRITE)));
Predicate predicateLatestUsers = subRootLatestUsers.get(ApplicationUser_.LAST_WRITE).in(sqLatestUsers);
Subquery<ApplicationUser> sq = c.subquery(ApplicationUser.class);
Root<Demographic> subRoot = sq.from(Demographic.class);
sq.select(subRoot.<ApplicationUser>get(Demographic_.USER)).where(predicateLatestUsers);
Predicate containsUsers = subRoot.get(Demographic_.USER).in(sq);
c.select(root).where(containsUsers);
The code compiles and successfully deploys in Wildfly 14, but when I execute the code, the get the following error (with white space to improve readability):
Invalid path: 'generatedAlias2.user' : Invalid path: 'generatedAlias2.user'
...
Caused by: org.hibernate.hql.internal.ast.QuerySyntaxException: Invalid path: 'generatedAlias2.user' [
select generatedAlias0 from com.company.model.Demographic as generatedAlias0
inner join fetch generatedAlias0.user as generatedAlias1
where generatedAlias2.user in (
select generatedAlias2.user from com.company.model.Demographic as generatedAlias2 where generatedAlias3.lastWrite in (
select max(generatedAlias3.lastWrite) from com.company.model.StarfishUser as generatedAlias3
)
)
]
Is chaining subqueries (nested subqueries) allowed by the JPA spec? Did I find something that is syntactically correctly but not actually allowed?

Answer 1

I figure out how to get the subquery to work. First is my updated Utility method
public static <R, T> Subquery<T> getLatestSubelement(CriteriaBuilder cb, CriteriaQuery<R> c, Class<T> clazz, SingularAttribute<T, Instant> attribute) {
//Get latest timestamp
Subquery<Instant> sq = c.subquery(Instant.class);
Root<T> subRoot = sq.from(clazz);
sq.select(cb.greatest(subRoot.<Instant>get(attribute)));
//Get object with the latest timestamp
Subquery<T> sq2 = c.subquery(clazz);
Root<T> subRoot2 = sq2.from(clazz);
sq2.where(subRoot2.get(attribute).in(sq));
return sq2;
}
Here is the code that uses the utility method
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Demographic> c = cb.createQuery(Demographic.class);
Root<Demographic> root = c.from(Demographic.class);
joinType = JoinType.INNER;
//use fetch instead of join to prevent duplicates in Lists
root.fetch(Demographic_.user, joinType);
Subquery<ApplicationUser> sq = JpaUtil.getLatestSubelement(cb, c, ApplicationUser.class, ApplicationUser_.lastWrite);
c.where(root.get(Demographic_.user).in(sq));
TypedQuery<Demographic> q = em.createQuery(c);
Stream<Demographic> stream = q.getResultStream();