Question

我使用带有JPQL分组选择的弹簧数据，一切正常并统计数据，但是当我想访问竞争对象时我得到了这个错误：

org.hibernate.LazyInitializationException: could not initialize proxy - no Session

我想要为统计数据收集这些实体

@Entity
public class BetCourse {

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "MATCH_ID", nullable = false)
    private BetMatch betMatch;
}

@Entity
public class BetMatch {

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "betMatch")
    private List<BetCourse> courses = new ArrayList<>();
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "COMPETITION_ID", nullable = false)
    private Competition competition;
}

@Entity
public class Competition {

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "competition")
    private List<BetMatch> betMatches = new ArrayList<>();
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "competition")
    private List<Stats> stats = new ArrayList<>();
}

我正在将这些类中的数据挖掘到Stats类

@Entity
public class Stats {

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "COMPETITION_ID", nullable = false)
    private Competition competition;
}

通过此选择：

@Query("select new Stats(" +
            "c.course, " +
            "c.courseType, " +
            "count(*), " +
            "SUM(CASE WHEN win = true THEN 1 ELSE 0 END), " +
            "c.betMatch.competition) " +
            "from BetCourse c " +
            group by c.course, c.betMatch.competition, c.courseType")
    public List<Stats> computeStatsByBetShop();

当我访问competiton对象时

stat.getCompetition()

我该如何获取此对象？是否有可能以某种方式与联接获取结合？

Answer 1

在创建了一些代码峰值之后，我找到了一个非常简单易懂的解决方案。不是从BetCourse表开始你的JPQL，而是从那里进行连接，你应该从Competition表开始，然后进行内部连接，直到BetCourse。

这是因为从BetCourse的角度来看，实体是一个ManyToOne，而JPA以某种方式迷失了它们。只是按相反的顺序解决你的问题。

@Query("select new Stats(" +
        "c.course, " +
        "c.courseType, " +
        "count(c), " +
        "SUM(CASE WHEN win = true THEN 1 ELSE 0 END), " +
        "cpt) " +
        "from Competition cpt " +
        "inner join cpt.betMatches bm " +
        "inner join bm.courses c " +
        "group by c.course, c.courseType, cpt")
@ReadOnlyProperty
public List<Stats> computeStatsByBetShop();

这里有一个GitHub minimum code跟随你的课程，所以你可以用它作为例子，以防它仍然不适合你。

干杯，尼古拉斯

如何通过与下一个其他对象相关的spring数据（jpql）获取对象

1 个答案: