Multiple writable mappings exist for the field. Only one may be defined as writable, all others must be specified read-only.

In entity bean, the foreign key usually replaced by the referential relationship such as :

public class Status implements Serializable {
    /**
     *
     */
    private static final long serialVersionUID = 1L;

    @Column(name="creation_datetime", nullable = false)
    private Timestamp creationDatetime;

    @Id
    @Column(name="seq_no", nullable = false)
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer seqNo;

    @Column(name="status", nullable = false)
    private String status;

    @Column(name="car_id", nullable = false, insertable=false, updatable=false)
    private String carId;

    @ManyToOne
    @JoinColumn(name = "car_id")
    private Transaction transaction;

    public Status() {
    }

    public Status(Timestamp creation_datetime,
                          Transaction transaction,
                          Integer seqNo, String status, String carId) {
        this.creationDatetime = creation_datetime;
        this.transaction = transaction;
        this.seqNo = seqNo;
        this.status = status;
        this.carId = carId;
    }
}

The foreign key is carId. It is exists in the relationship  
@ManyToOne
@JoinColumn(name = "car_id")
private Transaction transaction;
Eclipse will not generate the carId field for you. You required to explicitly create a read only field by annotation insertable=false, updatable=false. Otherwise, exception: Multiple writable mappings exist for the field [status.car_id]. Only one may be defined as writable, all others must be specified read-only will be thrown.