How to allow duplicates in an arrayList when using JPA?

Question

I keep getting "java.lang.IllegalStateException: Multiple representations of the same entity" even though I have the @Id set as true and I'm using a one to many relation on my variable.

Here are the classes which I'm trying to relate to one another:

@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;
    }

}

I want to have JPA create another table that relates to this one simple based on the name variable but whenever I try to add to the list and save to the DB I get

java.lang.IllegalStateException: Multiple representations of the same entity

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

You have used the private String area field as the primary key for entity AlternativeAreaName. So when you are trying to add

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

Both of them have the same primary key. So it is throwing the above exception.

To generate the primary key for JPA entity, please check

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

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