Question

我正在寻找一些帮助，因为我有点困惑

我创建了一个存储用户标记的实体

基本上我想创建一个要使用的命名查询，并且一个自动计算平均值，唯一的问题是我只希望选择的列被平均

目前表格是：

@Entity(name = "MARKING")
public class Marking implements Serializable {

    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToOne
    private Person marker;

    @ManyToOne
    private Project project;


    private String markingCompleted, markSectionOne, markSectionTwo, markSectionThree, markSectionFour,
            markSectionFive, markSectionSix, markSectionSeven, markSectionEight,
            markSectionNine, markSectionTen, markSectionEleven, markSectionTwelve, markSectionThirteen, markAdjust, overalMark, thirdMarker, plagorism;

我要问的是，我应该如何构建只能得出marksSectionOne的平均值的查询 - 十三

谢谢你们

编辑

我已将此添加到我的Facade中，但它似乎不对吗？

public TypedQuery<Double> markingAvg(Project id) {
    System.out.println("id = " + id);
    TypedQuery<Double> query = em.createQuery("select ((m.markSectionOne + m.markSectionTwo + m.markSectionThree + "
            + "m.markSectionFour + m.markSectionFive + m.markSectionSix + m.markSectionSeven +"
            + "m.markSectionEight + m.markSectionNine + m.markSectionTen + m.markSectionEleven +"
            + "m.markSectionTwelve + m.markSectionThirteen) / 13.0) from Marking m where m.project = :id", Double.class);
    query.setParameter("id", id);
    double avg = query.getSingleResult();
    return null;
}

Answer 1

第一种方法是计算数据库端的平均值，然后检索结果：

TypedQuery<Double> query = em.createQuery("select ((m.markSectionOne + ... + m.markSectionThirteen) / 13.0) from Marking m where m.id = :id", Double.class);
query.setParameter....
double avg = query.getSingleResult();

其他方法是选择您的实体，然后在java中计算平均值：

TypedQuery<Marking> query = em.createQuery("select m from Marking m where m.id = :id", Marking.class);
query.setParameter....
Marking m = query.getSingleResult();
int sum = m.getMarkSectionOne() + ... + m.getMarkSectionThirteen();
double avg = sum / 13.0;

命名查询以计算出平均值

1 个答案: