如何使用子选择为查询编写HIbernate Criteria

Question

我有两个实体Issue和Issue_Tracker。我正在使用hibernate 3.6和一对多关联。

issue.Java

public class Issue implements Serializable {
        private Integer issue_id;
        private String  issue_description;
        private Date issue_raised_date;
        private Set<Issue_Tracker> issueTracker = new HashSet<Issue_Tracker>(0);

        @OneToMany(fetch=FetchType.LAZY, mappedBy="issue_id")
        public Set<Issue_Tracker> getIssueTracker() {
        return issueTracker;
}

public void setIssueTracker(Set<Issue_Tracker> issueTracker) {
    this.issueTracker = issueTracker;

issue_tracker.Java

public class Issue_Tracker implements Serializable
{  
     private Integer   issue_id;
     private String    tracker_status;
     private Timestamp tracked_time;**

这是sql查询，如何使用条件实现此目的

SELECT i.issue_id, i.issue_description,
       it.tracker_status, it.tracked_time
FROM issues i 
LEFT JOIN ( SELECT it.issue_id, it.tracker_status, it.tracked_time 
            FROM issue_tracker it 
            INNER JOIN (SELECT issue_id, MAX(tracked_time) tracked_time 
                        FROM issue_tracker GROUP BY issue_id
                       ) A ON it.issue_id = A.issue_id AND it.tracked_time = A.tracked_time 
          ) it ON i.issue_id = it.issue_id 
WHERE i.status = "Escalate To";

Answer 1

首先，我建议您将Issue.issue Tracker的混淆名称更改为Issue.issue Trackers，因为它是一个Set。在查询时，它使事情更容易阅读。但是无所谓。

在Criteria API中，我认为您无法直接翻译此SQL。你最好写一个你想要的结果集的描述。您是否希望所有问题的最后跟踪时间为“Escalate To”状态？如果是这样，那应该接近你想要的。

    DetachedCriteria inner = DetachedCriteria.forClass(IssueTracker.class, "inner")
        .setProjection(Projections.max("inner.tracked_time"));

    Criteria crit = session.createCriteria(Issue.class, "issue");

    // Add the join with an ON clause (I am not sure why you need the LEFT JOIN)
    crit.createAlias("issueTracker", "it", Criteria.LEFT_JOIN, 
        Subqueries.eqProperty("it.tracked_time", inner));

    // Specify the SELECT fields
    crit.setProjections(Projections.projectionList()
            .add(Projections.property("issue_id"))
            // etc
            .add(Projections.property("it.tracked_time"));

    crit.add(Restrictions.eq("status", "Escalate To");

    List<Object[]> rows = crit.list();