JPA Null or zero primary key encountered in unit of work clone

Question

I learn about JPA and had task to make database and insert some values to it. I wondered how I can find out what was the ID of recently inserted object, so I found a way that I need to use flush method of EntityManager.

Unfortunately I got the

Null or zero primary key encountered in unit of work clone

exception when I use the above method. I think the problem lies in that my database has all ID's set on autoincrement ( I use ORACLE 11G Express ), so before commiting it has null value and it rollbacks transaction.

What I can do to fix it ?

This is DB ( ID's are autoincrement[Sequences and Triggers in oracle]):

public class Client {    
    public static void main(String[] args) {
        EntityManagerFactory emf =
                Persistence.createEntityManagerFactory("JpaIntroductionPU");        
        EntityManager em = emf.createEntityManager();
        EntityTransaction et = em.getTransaction();

        et.begin();

        Address ad1 = new Address();
        ad1.setStreet("Skaraktki");
        ad1.setCode("64-340");

        em.persist(ad1);
        em.flush();

        System.out.println(ad1.getAId());
        et.commit();
    }   
}

Address class

@Entity
@Table(name = "ADDRESS")
@NamedQueries({
    @NamedQuery(name = "Address.findAll", query = "SELECT a FROM Address a"),
    @NamedQuery(name = "Address.findByAId", query = "SELECT a FROM Address a WHERE a.aId = :aId"),
    @NamedQuery(name = "Address.findByStreet", query = "SELECT a FROM Address a WHERE a.street = :street"),
    @NamedQuery(name = "Address.findByCode", query = "SELECT a FROM Address a WHERE a.code = :code")})
public class Address implements Serializable {
    private static final long serialVersionUID = 1L;
    // @Max(value=?)  @Min(value=?)//if you know range of your decimal fields consider using these annotations to enforce field validation
    @Id
    @Basic(optional = false)
    @Column(name = "A_ID")
    private BigDecimal aId;

    @Basic(optional = false)
    @Column(name = "STREET")
    private String street;

    @Basic(optional = false)
    @Column(name = "CODE")
    private String code;

    @OneToOne(cascade = CascadeType.ALL, mappedBy = "aId")
    private Employee employee;

    @OneToOne(cascade = CascadeType.ALL, mappedBy = "aId")
    private Department department;

    public Address() {
    }

    public Address(BigDecimal aId) {
        this.aId = aId;
    }

    public Address(BigDecimal aId, String street, String code) {
        this.aId = aId;
        this.street = street;
        this.code = code;
    }

    public BigDecimal getAId() {
        return aId;
    }

    public void setAId(BigDecimal aId) {
        this.aId = aId;
    }

    public String getStreet() {
        return street;
    }

    public void setStreet(String street) {
        this.street = street;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public Employee getEmployee() {
        return employee;
    }

    public void setEmployee(Employee employee) {
        this.employee = employee;
    }

    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }       

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (aId != null ? aId.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof Address)) {
            return false;
        }
        Address other = (Address) object;
        if ((this.aId == null && other.aId != null) || (this.aId != null && !this.aId.equals(other.aId))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "jpaintroduction.Address[ aId=" + aId + " ]";
    }

}

Answer 1

This happend to me because I manually added an entry to my database with the id 0 (zero). In my case EclipseLink "couldn't" handle an id with zero. So I added following to my persistence.xml:

     <property name="eclipselink.allow-zero-id" value="true"/>

This property says EclipseLink to handle zero as a valid id.

[1] http://meetrohan.blogspot.de/2011/11/eclipselink-null-primary-key.html

Answer 2

You need to annotate your id field with @GeneratedValue, in order for JPA to know that the DB will generate the id automatically:

@Id
@Basic(optional = false)
@Column(name = "A_ID")
@SequenceGenerator( name = "mySeq", sequenceName = "MY_SEQ", allocationSize = 1, initialValue = 1 )
@GeneratedValue(strategy=GenerationType.IDENTITY, generator="mySeq")
private BigDecimal aId;

With oracle you can use GenerationType.IDENTITY and @SequenceGenerator in which case you don't need a trigger to query the sequence and populate the ID, JPA will do it for you. I'm not sure if GenerationType.AUTO will work with oracle but if it does, you'd need a trigger to query the sequence and populate the id. GenerationType.TABLE is the most portable solution, since you use an independent table managed by JPA to store the sequence, it works across all databases.

Check the docs in the link above.