在一个 jpql 查询中按每种类型获取一些记录

Question

我有两个实体——Person 和 Record：

@Entity
public class Person {
    @Id
    @GeneratedValue
    private Long id;

    @JsonIgnore
    @OneToMany(mappedBy = "person", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<Record> records;
}


@Entity
public class Record {
@Id
    @GeneratedValue
    private Long id;

@ManyToOne
    @JoinColumn(name = "person", referencedColumnName = "id", nullable = false)
    private Person person; 
}

我需要在一个查询中为每个现有人员获取 5 条记录。

我为 jpql 找到的唯一解决方案如下所示：

"SELECT r FROM Person p LEFT JOIN p.records r WHERE r.id IN " +
            "(SELECT r1.id FROM Record r1 WHERE r1.person = p AND " +
            "(SELECT Count(r2) FROM Record r2 WHERE r2.person = r1.person AND r2.id < r1.id) <= 5)

但在 spring jpa 中可能有更优雅的解决方案。

有人知道吗？

Answer 1

您可以在 ToMany 一侧使用 javax.validation.constraints.Size 注释来限制 ma​​x 括号

//..ToMany and other annotations
@javax.validation.constraints.Size(min=0, max=5)
private List<Record> records;