JPA CriteriaQuery Order By Latest Child Property

Question

I've got 2 entities: Project and ProjectStatus.

Project Entity:

@Entity
public class Project {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    Long id;

    @OneToMany(mappedBy = "project")
    private List<ProjectStatus> projectStatusses;
}

Project Status Entity:

@Entity
public class ProjectStatus {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    Long id;

    @ManyToOne
    private Project project;

    @Enumerated(EnumType.STRING)
    private ProjectStatusType statusType;
}

I would like to order projects by their latest status type with CriteriaQuery.orderBy .

I came up with the following:

CriteriaQuery<Project> criteriaQuery = criteriaBuilder.createQuery(Project.class);
Root<Project> root = criteriaQuery.from(Project.class);
Join<Project, ProjectStatus> join = root.join("projectStatusses", JoinType.LEFT);
criteriaQuery.orderBy(criteriaBuilder.asc(join.get("statusType")));

I want the above query to only take the latest project status into account, but I do not know how to do that. How can I achieve this?

Update: The sql to achieve this is:

SELECT proj.*, stat.statustype 
FROM project proj
LEFT JOIN projectStatus stat ON proj.id = stat.project_id
WHERE stat.id = (SELECT MAX(id) FROM projectstatus WHERE project_id = proj.id)
ORDER BY stat.statustype

Answer 1

I am not a fan of answering my own question, but I found the solution. Hopefully it will help somebody else.

My fault was to look for a solution in the criteriaQuery.orderBy method. Adding a subquery in the criteriaQuery.where method did the trick.

Solution:

    CriteriaQuery<Project> criteriaQuery = criteriaBuilder.createQuery(Project.class);
    Root<Project> root = criteriaQuery.from(Project.class);
    Join<Project, ProjectStatus> join = root.join("projectStatusses", JoinType.LEFT);

    //Create a subquery to get latest ProjectStatus for project
    Subquery sq = criteriaBuilder.createQuery().subquery(Long.class);
    Root<T> from = sq.from(Project.class);
    Path<ProjectStatus> path = root.join("projectStatusses");
    //Get latest status
    sq.select(criteriaBuilder.max(path.<Long>get("id")));
    //For each project
    sq.where(criteriaBuilder.equal(from.<Long>get("id"), root.<Long>get("id")));
    Predicate latestStatusCondition = criteriaBuilder.and(criteriaBuilder.equal(join.get("id"), sq));

    criteriaQuery.orderBy(criteriaBuilder.asc(join.get("statusType")));
    criteriaQuery.where(latestStatusCondition);