java - 如何使用子关联属性作为 JPA 父实体中的映射键

Question

我有两个实体 Car和 CarDescription其中 CarDescription取决于表 Language 中的另一个外键.

我想要完成的是拥有一个 HashMap在 Car这样每当我有一个Car entity-object 我能够从语言 id 访问所有描述。

实体Car.java

@Entity
@Table(name = "Car")
public class Car extends AbstractTimestampEntity implements Serializable {
    private static final long serialVersionUID = -5041816842632017838L;

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name = "ID", unique = true, nullable = false)
    private Long id;

    @OneToMany(mappedBy="car")
    @MapKeyColumn(name = "language_ID")
    // @MapKey(name = "language") // does not work either 
    private Map<Long, CarDescription> carDescription = new HashMap<>(0);
}

实体CarDescription.java

@Entity
@Table( name="car_description",
        uniqueConstraints = {
            @UniqueConstraint(columnNames={"language_id", "name"}) 
        }
)
public class CarDescription extends AbstractTimestampEntity implements Serializable {
    private static final long serialVersionUID = 2840651722666001938L;

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name = "ID", unique = true, nullable = false)
    private Long id;

    @NotNull
    @ManyToOne
    private Car car;

    @NotNull
    @OneToOne
    private Language language;

    // ..
}

实体Language.java

@Entity
public class Language implements Serializable {
    private static final long serialVersionUID = 3968717758435500381L;

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="ID")
    private Long id;

    // ..
}

我遇到的问题是映射为我提供了每个 CarDescription.id 的映射至 CarDescription .

我怎样才能完成正确的映射？

Answer 1

在 CarDescription 中，您需要添加 languageId 属性:

@Column(name = "language_id", insertable = false, updatable = false)
private Long languageId;

@NotNull
@OneToOne
@JoinColumn(name = "language_id")
private Language language;

public void setLanguage(Language language) {
    this.languageId = language.getId();
    this.language = language;
} 

然后你可以像这样在 Car 实体中使用它:

@OneToMany(mappedBy="car")
@MapKey(name = "languageId")
private Map<Long, CarDescription> carDescription = new HashMap<>(0);