Java Spring JPA 关系 @OneToMany 与第三列

Question

我在 java 中有两个实体(学生和组)，具有 @OneToMany 关系

public class Group {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;

@Column(name="name")
private Integer groupName;

public Group(Integer groupName) {
    this.groupName = groupName;
}

@OneToMany
@JoinTable(name = "groups_students",
        joinColumns= @JoinColumn(name = "group_id"),
        inverseJoinColumns = @JoinColumn(name = "student_id")
)
private Set<Student> students;
}   

我在本地主机上的表groups_students 中有第三列date。 date 不是类中的字段。我需要在 @Query 中获取它。任何人都可以帮助我如何获得此信息(也许向代码提供有关此日期列的信息或任何其他方式)

public class Student {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;

@Column(name="first_name")
private String firstName;

@Column(name="last_name")
private String lastName;

public Student(String firstName, String lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
}
}

Answer 1

处理连接表中的附加属性的方法是将其定义为单独的实体，然后使用中间实体拆分关系

@Entity
@Table(name = "groups_students")
public class GroupStudent {

    @Id
    @ManyToOne(fetch = FetchType.LAZY)
    private Group group;

    @Id
    @ManyToOne(fetch = FetchType.LAZY)
    private Student student;

    @Column(name = "date")
    private Date date;

    //getter-setter
}

现在修改Group实体上的关系

@OneToMany(mappedBy = "group", cascade = CascadeType.ALL)
private List<GroupStudent> groupStudents = new ArrayList<>();

并修改Student实体关系

@OneToMany(mappedBy = "student", cascade = CascadeType.ALL)
private List<GroupStudent> groupStudents = new ArrayList<>();

现在，如果您想查询诸如日期之类的附加属性，您可以使用这样的JPQL(例如，如果您想获取日期为过去日期的组中的所有学生) )

@Query(SELECT s FROM Student s JOIN s.groupStudents gs WHERE gs.group = :group and gs.date < CURRENT_DATE)