java - JPA 中复合键的唯一约束

Question

我有一个带有两个外键的实体，我也想将其用作约束JPA 有没有办法定义一个约束，该约束只有在以下情况下才是唯一的:重复相同的 FROM_CURRENCY_ID 和 TO_CURRENCY_ID，但允许 if 值FROM_CURRENCY_ID 和 TO_CURRENCY_ID 的反转

@Entity
@Table(name="CURRENCY_CONVERSION")
public class CurrencyConversion extends BaseEntity {

    private static final long serialVersionUID = -2440725717151990999L;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "FROM_CURRENCY_ID")
    private Currency fromCurrencyId;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "TO_CURRENCY_ID")
    private Currency toCurrencyId;

    @Column(name = "CURRENCY_RATE", nullable = false)
    private Double rate;
    // getter setters

}

Answer 1

向@Table注释添加唯一约束定义

@Table(
    uniqueConstraints=
        @UniqueConstraint(columnNames={"column_1", "column_2"})
)