Hibernate 双向@OneToMany 映射返回列 'xxx' 不能为 null

Question

I have a problem with Hibernate bidirectional @OneToMany mapping. This is my root entity:

@Entity(name = "Proposta")
@Table(name = "PROPOSTA")
public class Proposta implements Serializable {
        
   private static final long serialVersionUID = -705828064150128352L;
        
   public Proposta() {
       super();
   }
            
   @Id
   @Column(name = "COD_PROPOSTA")
   private Integer codProposta; 
            
   @OneToMany(mappedBy="proposta", fetch=FetchType.EAGER)
   @Cascade({ CascadeType.ALL })
   private List<PropostaUL> listaPropostaUl;

}

This is my child entity:

@Entity(name = "PropostaUL")
@Table(name = "PROPOSTA_UL")
public class PropostaUL {
        
   public PropostaUL() {
      super();
   }
    
   @Id
   @Column(name = "COD_FONDO_UE_UL")
   private String codFondoUeUl; 
        
   @ManyToOne(fetch = FetchType.EAGER)
   @JoinColumn(name = "COD_PROPOSTA")
   private Proposta proposta;

}

When I read the values of the two tables everything works properly; when I try to save it instead I have the following error

gen 05, 2021 10:14:03 AM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
WARN: SQL Error: 1048, SQLState: 23000
gen 05, 2021 10:14:03 AM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
ERROR: Column 'COD_PROPOSTA' cannot be null
gen 05, 2021 10:14:03 AM org.hibernate.engine.jdbc.batch.internal.AbstractBatchImpl release
INFO: HHH000010: On release of batch it still contained JDBC statements

The save call it the following

protected Object saveOrUpdate(Object obj, List<String> errorLog) {
   Transaction transaction = null;
   try {
      if (session == null || ! session.isOpen()) {
         session = HibernateFactory.getSessionFactory().openSession();
      } 
      transaction = session.beginTransaction();
      session.saveOrUpdate(obj);
      transaction.commit();
   } catch (HibernateException e) {
      obj = null;
      errorLog.add(e.getMessage());
   } finally {
      if (session != null) {
         session.close();
      } 
   }
   return obj;
}

I read other same problems in the forum but all the solutions suggested doesn't worked. I checked this site too

https://vladmihalcea.com/the-best-way-to-map-a-onetomany-association-with-jpa-and-hibernate/

and even if the case analyzed seems the same, and the configuration too, the problem persists. The value of COD_PROPOSTA in the root entity is provided and it is not null . Do you have any suggestion on how to solve the problem?

Answer 1

The column "COD_PROPOSTA" and "COD_FONDO_UE_UL" marked as Id cannot be null and you are not giving any value to that property (unless you do it manually once created the object). To give an Id automatically you can add the annotation @GeneratedValue to codProposta and codFondoUeUl .

Answer 2

As it stated in the documentation :

Whenever a bidirectional association is formed, the application developer must make sure both sides are in-sync at all times.

So you should add addPropostaUl() and removePropostaUl() utility methods that synchronize both ends whenever a child element is added or removed:

@Entity
public class Proposta implements Serializable {
    
   // ...
        
   @OneToMany(mappedBy = "proposta", fetch = FetchType.EAGER)
   @Cascade(CascadeType.ALL)
   private List<PropostaUL> listaPropostaUl;
 
   public void addPropostaUl(PropostaUL propostaUl) {
      listaPropostaUl.add(propostaUl);
      propostaUl.setProposta(this);
   }

   public void removePropostaUl(PropostaUL propostaUl) {
      listaPropostaUl.remove(propostaUl);
      propostaUl.setProposta(null);
   }
}

and then use only these methods when you want modify this association.

Example (adding new PropostaUL to the existent Proposta ):

Transaction transaction = session.beginTransaction();

Proposta proposta = session.load(Proposta.class, propostaId);
PropostaUL newPropostaUL = new PropostaUL();
// ...
proposta.addPropostaUl(newPropostaUL);
session.saveOrUpdate(proposta);

transaction.commit();

Answer 3

Thanks all for your answers.
I found the problem.
The object that I have to save is json object converted in Java object via Jackson library.
So I added @JsonManagedReference and @JsonBackReference to the objects and it works.
This is the right code

@Entity(name = "Proposta")
@Table(name = "PROPOSTA")
public class Proposta implements Serializable {
        
   private static final long serialVersionUID = -705828064150128352L;
        
   public Proposta() {
       super();
   }
            
   @Id
   @Column(name = "COD_PROPOSTA")
   private Integer codProposta; 
            
   @JsonManagedReference
   @OneToMany(mappedBy="proposta", cascade = CascadeType.ALL, fetch=FetchType.LAZY)
   private List<PropostaUL> listaPropostaUl;

}

and the PropostaUL object

@Entity()
@Table(name = "PROPOSTA_UL")
public class PropostaUL {
    
    public PropostaUL() {
        super();
    }

    @Id
    @Column(name = "COD_FONDO_UE_UL")
    private String codFondoUeUl;    
    
    @JsonBackReference
    @ManyToOne
    @JoinColumn(name = "COD_PROPOSTA")
    private Proposta proposta;
 }