java - 外键 Hibernate 注释

Question

我无法使这个简单的外键约束起作用。

@Entity
@Table(name = "wheel")
@Data
public class WheelEntity {
    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;
    ...

@Entity
@Table(name = "bike")
@Data
public class BikeEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @ManyToOne(targetEntity = WheelEntity.class, fetch=FetchType.EAGER, cascade={CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REMOVE})
    @JoinColumn(name = "wheel_1_id", referencedColumnName = "id")
    @NotNull
    private Integer wheel_1_id;

    @ManyToOne(targetEntity = WheelEntity.class, fetch=FetchType.EAGER, cascade={CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REMOVE})
    @JoinColumn(name = "wheel_2_id", referencedColumnName = "id")
    @NotNull
    private Integer wheel_2_id;
    ...

当我想插入一辆新自行车时，以下是持久保存 BikeEntity 时遇到的错误:

Caused by: java.lang.IllegalArgumentException: Can not set java.lang.Integer field com.xxx.xxx.xxx.storage.WheelEntity.id to java.lang.Integer
    at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:167)
    at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:171)
    at sun.reflect.UnsafeFieldAccessorImpl.ensureObj(UnsafeFieldAccessorImpl.java:58)
    at sun.reflect.UnsafeObjectFieldAccessorImpl.get(UnsafeObjectFieldAccessorImpl.java:36)
    at java.lang.reflect.Field.get(Field.java:393)
    at org.hibernate.property.access.spi.GetterFieldImpl.get(GetterFieldImpl.java:39)

无法将 java.lang.Integer 设置为 java.lang.Integer。嗯嗯嗯？奇怪!

非常感谢您的帮助

Answer 1

在 Hibernate 中，您可以通过在 Entity2 中引用 Entity1 来创建关系。正确的做法是:

@Entity
@Table(name = "wheel")
@Data
public class WheelEntity {
    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;
    ...

@Entity
@Table(name = "bike")
@Data
public class BikeEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @ManyToOne(targetEntity = WheelEntity.class, fetch=FetchType.EAGER, cascade={CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REMOVE})
    @JoinColumn(name = "wheel_1_id", referencedColumnName = "id")
    @NotNull
    private WheelEntity wheelEntity;