[英]Hibernate many-to-one mapping sets foreign key null
學生有多台筆記本電腦。 學生 oneToMany 筆記本電腦映射
學生.java
import java.util.ArrayList;
import java.util.List;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToMany;
@Entity
public class Student {
@Id
private int id;
private StudentName studentName;
private String email;
@OneToMany(mappedBy = "student")
private List<Laptop> laptops = new ArrayList<Laptop>();
public Student() {
}
public Student(int id, StudentName studentName, String email) {
this.id = id;
this.studentName = studentName;
this.email = email;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public StudentName getStudentName() {
return studentName;
}
public void setStudentName(StudentName studentName) {
this.studentName = studentName;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public List<Laptop> getLaptop() {
return laptops;
}
public void setLaptop(List<Laptop> laptops) {
this.laptops = laptops;
}
@Override
public String toString() {
return "Student [id=" + id + ", studentName=" + studentName + ", email=" + email + "]";
}
}
筆記本電腦.java
package com.practice.hibernateDemo.enity;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
@Entity
public class Laptop {
@Id
private int lid;
private String lName;
@ManyToOne
@JoinColumn(name="student_id", referencedColumnName="id")
private Student student;
public Laptop() {
}
public int getLid() {
return lid;
}
public void setLid(int lid) {
this.lid = lid;
}
public String getlName() {
return lName;
}
public void setlName(String lName) {
this.lName = lName;
}
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
@Override
public String toString() {
return "Laptop [id=" + lid + ", lName=" + lName + "]";
}
}
主class
package com.practice.hibernateDemo;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import com.practice.hibernateDemo.enity.Laptop;
import com.practice.hibernateDemo.enity.Student;
import com.practice.hibernateDemo.enity.StudentName;
public class CreateStudent {
public static void main(String[] args) {
Laptop laptop = new Laptop();
laptop.setLid(100);
laptop.setlName("HP");
Student student = new Student();
student.setId(101);
student.setEmail("test@gmail.com");
student.setStudentName(new StudentName("test1","test2", "test3"));
student.getLaptop().add(laptop);
Configuration con = new Configuration().configure().addAnnotatedClass(Student.class).addAnnotatedClass(Laptop.class);
SessionFactory sf = con.buildSessionFactory();
Session session = sf.getCurrentSession();
Transaction tx = session.beginTransaction();
session.save(laptop);
session.save(student);
tx.commit();
}
}
保存 object 后,筆記本電腦表中的外鍵設置為 null
蓋子 lName student_id 100 HP NULL
任何人都知道我在哪里做了錯誤的映射,因為我得到外鍵為 null
提前致謝
1:many 關系的“多”方始終是擁有方。 如果關系是雙向的,那么對方將攜帶一個mappedBy
屬性,就像雙向 1:1 關系的非擁有方一樣。 擁有方的關系字段對於將關系傳達給持久層是有意義的,而您沒有設置它。
例如,
laptop.setStudent(student);
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