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我嘗試JPA的一對一映射, 在這裏我已經採取了學生和聯繫之間的關係,每個學生都有聯繫。實體與內部類建設實體
我已創建學生實體如下,
@Entity
@Table(name="TBL_STUDENT")
public class Student implements Serializable{
public Student(){ }
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name="ID")
private Integer studentId;
@OneToOne(targetEntity=StudentContact.class,fetch=FetchType.LAZY)
@JoinColumn(name="CONTACT_ID")
private StudentContact contact;
....
....
....
}
現在StudentContact實體如下,
@Entity
@Table(name="TBL_STD_CONTACT")
public class StudentContact extends Serializable{
public StudentContact(){ }
@Id
@Column(name="ID")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer contactId;
...
...
// all the properties mapped,
public static class Builder{
private Integer contactId;
private String phoneNo;
private String streetAddr;
....
// all the properties as same as StudentContact
public Builder(String val){
this.city = val;
}
public Builder setContactId(Integer contactId) {
this.contactId = contactId;
return this;
}
// rest all the setter methods are like the above, having return type Builder
public StudentContact build(){
return new StudentContact(this);
}
}
private StudentContact(Builder builder){
this.contactId = builder.contactId;
this.city = builder.city;
this.phoneNo = builder.phoneNo;
.......
...
}
}
在上面StudentContact實體,你可以看到我已經創建了一個內部類生成器,其責任是通過使用其「構建」方法來構建StudentContact對象,您可以在下面提到的StudentTest類中看到
現在我有寫了一個StudentTest類具有的主要方法如下,
public class StudentTest {
public static void main(String [] args){
try{
StudentDAO dao = new StudentDAO();
Student student = dao.getEntity(110);
StudentContact contact = new StudentContact.Builder("Bhubaneshwar")
.setPhoneNo("9867342313")
.setPinCode("400392")
.setState("Odhisha").build();
student.setContact(contact);
dao.updateEntity(student);
}catch(Exception e){
e.printStackTrace();
}
}
當我運行StudentTest從NetBeans IDE中,它給作爲錯誤
Exception in thread "main" java.lang.VerifyError: Constructor must call super() or this() before return in method com.entities.StudentContact.<init>()V at offset 0
我無法理解這個錯誤,這是否錯誤是因爲我在StudentContact類已經創建了內部類,
我怎樣才能解決這個問題,
即使我在我的私人構造函數StudentContact中寫入super()或this()仍然會給出錯誤 – 2013-02-20 11:47:18
您還有其他問題; StudentContact _extends_ Serializable是一個 – 2013-02-20 11:49:21