如何在我的 springboot 项目中使用 JPA 注释使用唯一键约束？

Question

How to work multi-column constraint with JPA annotations in my springboot project? I'm trying to introduce a multi-key constraint on a JPA-mapped entity:

@Entity
@Table(name = "Student_Master",uniqueConstraints={
        @UniqueConstraint(columnNames = {"id","sr_no.", "roll_no"})
    })
public class StudentMaster implements Serializable{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Integer sId;// id same
    @Column(name = "sr_no.", length = 5,nullable = false,unique = true)//not null and sr no. should be unique
    private Integer srNo;
    @Column(name = "roll_no", length = 10,nullable = false,unique = true)
    private Integer rollNo;

Basically (id, sr_no,roll_no) pair should be unique, but I only found a way to say that id should be unique.

I have also declare unique constraints using the @Table(uniqueConstraints =...) annotation in your entity class.

But it's didn't work because entry the duplicate roll no and srNo also with different user.

Answer 1

You have the option to create an Embedded class , which contains your keys and reference it in your StudentMaster

For this you need @EmbeddedId in your Entity and @Embeddable over your key class:

@Embeddable
public class MyKey implements Serializable {
    @Column(name = "id")
    private Integer sId;// id same
    @Column(name = "sr_no.", length = 5, nullable = false, unique = true)//not null and sr no. should be unique
    private Integer srNo;
    @Column(name = "roll_no", length = 10, nullable = false, unique = true)
    private Integer rollNo;

    /** getters and setters **/
}

@Entity
public class StudentMaster implements Serializable {
    @EmbeddedId
    private MyKey myKey;
}

---

Or a way without having the embedded class you can use @IdClass(MyKey.class) . Now you can use the @Id over your key attributes

public class MyKey implements Serializable {
    private Integer sId;
    private Integer srNo;
    private Integer rollNo;

    /** getters and setters **/
}

@Entity
@IdClass(MyKey.class)
public class StudentMaster implements Serializable {
    @Id
    @Column(name = "id")
    private Integer sId;// id same
    @Id
    @Column(name = "sr_no.", length = 5, nullable = false, unique = true)//not null and sr no. should be unique
    private Integer srNo;
    @Id
    @Column(name = "roll_no", length = 10, nullable = false, unique = true)
    private Integer rollNo;
}