JPA CriteriaQuery按最新子项属性排序 [英] JPA CriteriaQuery Order By Latest Child Property

问题描述

我有2个实体：Project和ProjectStatus。

I've got 2 entities: Project and ProjectStatus.

项目实体：

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

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

项目状态实体：

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

    @ManyToOne
    private Project project;

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

我想按照最新状态订购项目 CriteriaQuery.orderBy 。

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

我想出了以下内容：

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")));

我希望上面的查询只考虑最新的项目状态，但我不知道如何要做到这一点。
如何实现这一目标？

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?

更新：
实现此目的的SQL是：

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

推荐答案

我不是回答我自己的问题的粉丝，但我找到了解决方案。希望它能帮助其他人。

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

我的错是在 criteriaQuery.orderBy 方法中寻找解决方案。在 criteriaQuery.where 方法中添加子查询可以解决问题。

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

解决方案：

    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);

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