如何為帶有子選擇的查詢編寫 HIbernate Criteria

Question

我有兩個實體Issue和Issue_Tracker 。 我正在使用 hibernate 3.6 和一對多關聯。

問題.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;**

這是sql 查詢，如何使用標准實現這一點

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，我建議您將令人困惑的 Issue.issueTracker 名稱更改為 Issue.issueTrackers，因為它是一個 Set。 它使您在查詢時更容易閱讀。 但是無所謂。

在 Criteria API 中，我認為您無法直接翻譯此 SQL。 你最好寫下你想要的結果集的描述。 您是否想要所有具有“升級到”狀態的問題的最后跟蹤時間？ 如果是這樣，這應該接近你想要的。

    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();