如何扩展@Entity

Question

This is my superclass

@Entity
@Table(name = "utente")
@Component
@Inheritance
public class Utente implements Serializable{

    private static final long serialVersionUID = -7124540331184173742L;

    @Id
    @GeneratedValue
    @Column(name = "id")
    private int id;

    @Column(name = "nome")
    @Size(min = 1, max = 20)
    @Pattern(regexp="^[A-Za-z 'òàùèéì]*$")      
    @NotBlank
    private String nome;

    @Column(name = "cognome")
    @Size(min = 1, max = 20)
    @Pattern(regexp="^[A-Za-z 'òàùèéì]*$")
    @NotBlank
    private String cognome;

    @Column(name = "email")
    @Email
    @Size(min = 1, max = 40)
    private String email;

    @OneToOne(mappedBy = "utente", cascade = CascadeType.ALL)
    @Valid
    private Autenticazione autenticazione;  

    @OneToMany(mappedBy = "utente", fetch = FetchType.EAGER,  orphanRemoval=true, cascade=CascadeType.ALL)  
    private List<Autorizzazioni> autorizzazioniLista;
}

This is the class that extend the one above:

@Entity
public class UtenteSubClass extends Utente{ 

@Transient
private String newField;
}

When I try to retrieve an object UtenteSubClass I get this error "org.hibernate.util.JDBCExceptionReporter - Unknown column 'this_.DTYPE' in 'where clause'" .

Probably my "mapping system" is wrong. Where is my error?

Thank you in advance.

Answer 1

If you choose to use SINGLE_TABLE inheritance (which is default for @Inheritance annotation without arguments in your code) then you should add @DiscriminatorColumn annotation to your superclass (and @DiscriminatorValue to extending classes). Otherwise via documentation :

If @DiscriminatorColumn is not specified on the root of the entity hierarchy and a discriminator column is required, the Persistence provider assumes a default column name of DTYPE and column type of DiscriminatorType.STRING.

hibernate just can't find this default column in your table. You can introduce your own descriminator column, or generate default one