Hibernate / JPA自動創建外鍵而不是在多對一關聯中使用現有外鍵

Question

我用：

• SpringBoot 1.5.1
• MariaDB / MySQL 10.1.14 / 15.1
• org.hibernate.dialect.MySQL5Dialect
• Hibernate5（SpringBoot默認）

這是SQL-Table-Definition：

CREATE TABLE salaries (
emp_no      BIGINT          NOT NULL,
salary      BIGINT          NOT NULL,
from_date   DATETIME        NOT NULL,
to_date     DATETIME        NOT NULL,
FOREIGN KEY (emp_no) REFERENCES employees (emp_no),
PRIMARY KEY (emp_no, from_date)
) 

這是關聯多方面的實體（使用嵌入式ID）：

@Entity
@Table(name = "salaries")
public class Salary {

    @EmbeddedId
    private EmpIdFromDatePK empId;

    @Column(name = "to_date", columnDefinition = "DATETIME")
    @Temporal(TemporalType.TIMESTAMP)
    private Date toDate;

    @Column(name = "salary")
    private Long salary;

    @ManyToOne(fetch = FetchType.LAZY)
    @Fetch(FetchMode.JOIN)
    @MapsId("empId")
    @JoinColumns({@JoinColumn(foreignKey = @ForeignKey(name = "salaries_ibfk_1"), name = "emp_no", referencedColumnName = "emp_no")})
    private Employee employee;

    public Salary() {
        super();
    }

    //...
}

關鍵類：

@Embeddable
public class EmpIdFromDatePK implements Serializable {

    @Column(name = "emp_no")
    private Long empId;

    @Column(name = "from_date", columnDefinition = "DATETIME")
    @Temporal(TemporalType.TIMESTAMP)
    private Date fromDate;

    public EmpIdFromDatePK() {
        super();
    }

    //....
} 

而協會一方的實體：

@Entity
@Table(name = "employees")
public class Employee {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "emp_no")
    private Long empId;

    //...

    @OneToMany(mappedBy = "employee")
    private List<Salary> salaryList;

    //...
}

問題：當我使用ManyToOne關聯時（例如，在員工加入工資記錄的選擇中），在數據庫中創建了第二個外鍵：

CONSTRAINT `FKjojacp79fphmajxrdll8fvf5o` FOREIGN KEY (`emp_no`) REFERENCES `employees` (`emp_no`),
CONSTRAINT `salaries_ibfk_1` FOREIGN KEY (`emp_no`) REFERENCES `employees` (`emp_no`)

問題：我該如何避免這種行為？

提前致謝

Answer 1

你可以嘗試：

@JoinColumn(name="emp_no", referencedColumnName="emp_no")
@ForeignKey(name="salaries_ibfk_1")

？

Answer 2

JPA 2.1僅支持通過@ForeignKey批注定義外鍵。

所以如果你使用JPA舊版本而不是2.1，我認為你不能這樣做