使用 JPA 时，如何允许 arrayList 中的重复项？

Question

我不断收到“java.lang.IllegalStateException：同一实体的多个表示”，即使我将 @Id 设置为 true 并且我在变量上使用了一对多关系。

以下是我试图相互关联的类：

@Entity
@Table(name = "map_area")
public class MapArea extends BasicModel {
   @Id
   @Column(nullable = false, unique = true)
   private String name;

   @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
   @JoinColumn(name = "area", referencedColumnName = "name")
   public List<AlternativeAreaName> alternativeNames;

    public MapArea() {}

    public MapArea(String name) {
        this.name = name;
        this.alternativeNames = new ArrayList<>();
    }

}

@Entity
@Table(name = "alternative_area_name")
public class AlternativeAreaName implements Serializable {

    @Id
    @Column(nullable = false, unique = false)
    private String area;

    @Column(nullable = true)
    private String alternativeName;

    public AlternativeAreaName(){}

    public AlternativeAreaName(String area, String alternativeName) {
        this.area = area;
        this.alternativeName = alternativeName;
    }

}

我想让 JPA 根据名称变量创建另一个与这个简单的表相关的表，但是每当我尝试添加到列表并保存到数据库时，我都会得到

java.lang.IllegalStateException：同一实体的多个表示

MapArea mapArea = new MapArea("example");
AlternativeAreaName altAreaName1 = new AlternativeAreaName("example", "alt example");
AlternativeAreaName altAreaName2 = new AlternativeAreaName("example", "alt example2");
mapArea.alternativeNames.add(altAreaName2);

mapAreaRepository.save(mapArea);

Answer 1

您已使用private String area字段作为实体 AlternativeAreaName 的主键。 所以当你试图添加

AlternativeAreaName altAreaName1 = new AlternativeAreaName("example", "alt example");
AlternativeAreaName altAreaName2 = new AlternativeAreaName("example", "alt example2");

它们都具有相同的主键。 所以它抛出了上述异常。

要为 JPA 实体生成主键，请检查

• https://www.objectdb.com/java/jpa/entity/id

• https://docs.oracle.com/cd/E16439_01/doc.1013/e13981/cmp30cfg001.htm