Cannot insert NULL into a fields in OneTomany JPA entity

Question

I have a OneToMany JPA entity association. My association in parent class is

@OneToMany(targetEntity = Extensions.class, cascade = CascadeType.ALL)
@JoinColumn(name = "EX_LOAN_ID",referencedColumnName = "LOAN_ID")
private List<Extensions> extensions;

Child Class
public class Extensions implements Serializable {
@Id
@Column(name = "EX_LOAN_ID")
private Long exLoanId;
@Id
@Column(name = "EX_NO")
private Long exNo;
@Column(name = "EX_EXTENSION_DAYS")
private Long exExtensionDays;

I am calling 
repository.saveAndFlush(next); 

The next object have all values but i am getting hibernate error message saying cannot insert null into EX_LOAN_ID

Answer 1

We do not recommend the use of unidirectional @OneToMany associations.

I believe that if you change this to a regular bidirectional @ManyToOne/@OneToMany, this problem will be resolved.

UPDATE

For example, I believe the following mapping would work for you:

@Entity
static class Loan {
    @Id
    @Column(name = "LOAN_ID")
    private Long id;

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "loan")
    private List<Extension> extensions = new ArrayList<>();
}

@Entity
static class Extension {
    @Id
    @Column(name = "EX_LOAN_ID")
    private Long exLoanId;

    @Id
    @Column(name = "EX_NO")
    private Long exNo;

    @Column(name = "EX_EXTENSION_DAYS")
    private Long exExtensionDays;

    @ManyToOne
    @JoinColumn(name = "EX_LOAN_ID", 
                insertable = false, updatable = false)
    private Loan loan;
}