Question

Hi all I’ve a small problem to map one-to-one using JPA 2 persistence with EclipseLink vendor and maybe any of you will be able to help.

I want to map one table with another but the field in second table is optional. So I’ve created @Entity for the first table:

Amp class

private AmpApInfo ampApInfo;
private String apid;


    @Id
@GeneratedValue(strategy=GenerationType.AUTO)
public String getApid() {
    return this.apid;
}


public void setApid(String apid) {
    this.apid = apid;
}

    @OneToOne
@JoinColumn(name="apid")
public AmpApInfo getAmpApInfo() {

        return this.ampApInfo;

}

public void setAmpApInfo(AmpApInfo ampApInfo) {
    this.ampApInfo = ampApInfo;
}

and @Entity for the second table

AmpApInfo class

    private String apid;
private Amp amp;
    private String prodOrderNo;

public AmpApInfo() {
}



@OneToOne(optional=true, mappedBy="ampApInfo")
public Amp getAmp() {
    return this.amp;
}

public void setAmp(Amp amp) {
    this.amp = amp;
}

    @Id
public String getApid() {
    return apid;
}
public void setApid(String apid) {
    this.apid = apid;
}

        @Column(name="prod_order_no")
public String getProdOrderNo() {
    return this.prodOrderNo;
}

public void setProdOrderNo(String prodOrderNo) {
    this.prodOrderNo = prodOrderNo;
}

Now when I want to find prodOrderNo like

    public Amp selectProdInfo(String name) {
    // TODO Auto-generated method stub


    Amp amp = Transactions.getEntityManager().find(Amp.class, name.trim());

    System.out.println("order number" + amp.getAmpApInfo().getProdOrderNo());

    return amp;
}

I’m expecting to get null cos its not there but I’m getting java.lang.NullPointerException on the line

  System.out.println("order number" + amp.getAmpApInfo().getProdOrderNo());

Any one can help???

Answer 1

Either amp is null or amp.getAmpApInfo() is returning null, and you are trying to call methods on them.