如何在JPA父实体中将子关联属性用作Map键 [英] How to use a child association property as a Map key in JPA parent entity

问题描述

我有两个实体 Car 和 CarDescription 其中 CarDescription 取决于表语言中的另一个外键。 我试图完成的是在 Car 中有一个 HashMap ，这样每当我有一个 Car entity-object我可以访问语言ID中的所有描述。

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）//不起作用
私人地图< 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 
私家车; 
 
 @NotNull 
 @OneToOne 
私有语言语言; 
 
 // .. 
} 
  

实体 Language.java

  @Entity 
 public class语言实现Serializable {
 private static final long serialVersionUID = 3968717758435500381L; 
 
 @Id 
 @GeneratedValue（strategy = GenerationType.IDENTITY）
 @Column（name =ID）
私人长ID; 
 
 // .. 
} 
  

我的问题是这个映射给了我一张从每个 CarDescription.id 到 CarDescription 的地图。

如何才能完成正确的映射？

解决方案

在 CarDescription 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语言语言; 
 
 public void setLanguage（Language language）{
 this.languageId = language.getId（）; 
 this.language = language; 
} 
  

然后你可以在 Car < code $>这样的实体：



  @OneToMany（mappedBy =car）
 @MapKey（name =languageId）
私人地图< Long，CarDescription> carDescription = new HashMap<>（0）; 
  




I'm having two entities Car and CarDescription where CarDescription is depending on another foreign key from the table Language.

What I' trying to accomplish is to have a HashMap in Car such that whenever I'm having a Car entity-object I am able to access all descriptions from the language id.

Entity 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);
}

Entity 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;

    // ..
}

Entity 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;

    // ..
}

The problem I am having is that the mapping gives me a map from each CarDescription.id to CarDescription.

How can I accomplish a correct mapping?

解决方案

In CarDescription you need to add the languageId property:

@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;
} 

Then you can use it in the Car entity like this:

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

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