在工作单元克隆中遇到JPA Null或零主键

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.

我了解JPA并且有任务创建数据库并为其插入一些值。我想知道如何找出最近插入的对象的ID是什么,所以我找到了一种方法,我需要使用EntityManager的flush方法。

Unfortunately I got the

不幸的是我得到了

Null or zero primary key encountered in unit of work clone

在工作单元克隆中遇到空或零主键

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.

我使用上述方法时的异常。我认为问题在于我的数据库在自动增量上设置了所有ID(我使用ORACLE 11G Express),因此在提交之前它具有空值并且它回滚事务。

What I can do to fix it ?

我能做些什么来修复它?

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

这是DB(ID是自动增量[oracle中的序列和触发器]):

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 + " ]";
    }

}

2 个解决方案

#1

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

您需要使用@GeneratedValue注释您的id字段,以便JPA知道DB将自动生成id:

@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.

使用oracle,您可以使用GenerationType.IDENTITY和@SequenceGenerator,在这种情况下,您不需要触发器来查询序列并填充ID,JPA将为您执行此操作。我不确定GenerationType.AUTO是否可以与oracle一起工作,但如果确实如此,你需要一个触发器来查询序列并填充id。 GenerationType.TABLE是最便携的解决方案,因为您使用由JPA管理的独立表来存储序列,它适用于所有数据库。

Check the docs in the link above.

检查上面链接中的文档。

#2

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:

这发生在我身上,因为我手动将一个条目添加到我的数据库,其id为0(零)。在我的情况下,EclipseLink“无法”处理一个零的id。所以我在persistence.xml中添加了以下内容:

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

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

此属性表示EclipseLink将零作为有效ID处理。

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

#1