下面是代码
package com.hibernate.mapping.mtm;
import java.util.ArrayList;
import java.util.List;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
/**
* @author Prajapati
*
*/
public class Main {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
SessionFactory sf= new Configuration().configure("com/hibernate/mapping/mtm/hibernate.cfg.xml").buildSessionFactory();
Session sn = sf.openSession();
Transaction tx = sn.beginTransaction();
Department dept1 = new Department();
dept1.setId(20l);
dept1.setDepartmentName("Development");
Department dept2 = new Department();
dept2.setId(10l);
dept2.setDepartmentName("Accounts");
Department dept3 = new Department();
dept3.setId(30l);
dept3.setDepartmentName("QA");
Department dept4 = new Department();
dept4.setId(40l);
dept4.setDepartmentName("Designing");
Employee emp1 = new Employee();
emp1.setEmployeeID(30l);
emp1.setEmployeeName("Michele");
Employee emp2 = new Employee();
emp2.setEmployeeID(40l);
emp2.setEmployeeName("Devendra");
Employee emp3 = new Employee();
emp3.setEmployeeID(50l);
emp3.setEmployeeName("Prabhat");
Employee emp4 = new Employee();
emp4.setEmployeeID(60l);
emp4.setEmployeeName("Himanshi");
Employee emp5 = new Employee();
emp5.setEmployeeID(70l);
emp5.setEmployeeName("Kanika");
List<Employee> employeesQA = new ArrayList<Employee>();
employeesQA.add(emp3);
employeesQA.add(emp2);
List<Employee> employeesDev = new ArrayList<>();
employeesDev.add(emp3);
employeesDev.add(emp4);
List<Employee> employeesAccounts = new ArrayList<>();
employeesAccounts.add(emp5);
employeesAccounts.add(emp1);
dept3.setEmployees(employeesQA);
dept1.setEmployees(employeesDev);
List<Department> departments = new ArrayList<Department>();
departments.add(dept1);
departments.add(dept2);
departments.add(dept3);
departments.add(dept4);
//emp5 works in all the departments
emp5.setDepartments(departments);
/*List<Department> departments3 = new ArrayList<Department>();
departments3.add(dept1);
departments3.add(dept2);
emp3.setDepartments(departments3);
*/
sn.save(emp5);
sn.save(dept3);
sn.save(dept1);
/**
* When i am running this program.
* Only mapping from department side is mapped and not from inverse side.How can i say this is a M2M
* while i am unable to Map from both the sides in terms of Hibernate
*/
// sn.save(p);
tx.commit();
sn.close();
}
}
package com.hibernate.mapping.mtm;
import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
@Entity
public class Department {
@Id
private Long id;
private String departmentName;
//@ManyToMany(cascade=CascadeType.ALL,mappedBy="departments")
@ManyToMany(cascade=CascadeType.ALL)
private List<Employee> employees;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getDepartmentName() {
return departmentName;
}
public void setDepartmentName(String departmentName) {
this.departmentName = departmentName;
}
public List<Employee> getEmployees() {
return employees;
}
public void setEmployees(List<Employee> employees) {
this.employees = employees;
}
}
package com.hibernate.mapping.mtm;
import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
@Entity
public class Employee {
@Id
private Long employeeID;
private String employeeName;
@ManyToMany(mappedBy="employees",cascade=CascadeType.ALL)
//Mapped by says here that go to employees in opposite table to get details of departments for employees and the key of the relationship is on the other side.
//i.e. you are considering department side the owner side now by saying mappedby.
//@ManyToMany(cascade=CascadeType.ALL)
private List<Department> departments;
public Long getEmployeeID() {
return employeeID;
}
public void setEmployeeID(Long employeeID) {
this.employeeID = employeeID;
}
public String getEmployeeName() {
return employeeName;
}
public void setEmployeeName(String employeeName) {
this.employeeName = employeeName;
}
public List<Department> getDepartments() {
return departments;
}
public void setDepartments(List<Department> departments) {
this.departments = departments;
}
}
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.driver_class">org.gjt.mm.mysql.Driver</property>
<property name="hibernate.connection.password">root</property>
<property name="hibernate.connection.url">jdbc:mysql://127.0.0.1/mapping</property>
<property name="hibernate.connection.username">root</property>
<!-- <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property> -->
<property name="hibernate.dialect">org.hibernate.dialect.MySQLInnoDBDialect</property>
<property name="hbm2ddl.auto">create</property>
<property name="show_sql">true</property>
<mapping class="com.hibernate.mapping.mtm.Employee"/>
<mapping class="com.hibernate.mapping.mtm.Department"/>
</session-factory>
</hibernate-configuration>
我很困惑为什么 Hibernate 没有保存 emp5 的所有条目，因为它在所有部门中都是如此，而且关系是多对多的，没有为员工 emp5 完成条目。
以下是包含相应数据的表格：
mysql> select * from employee;
| employeeID | employeeName |
| 40 | Devendra |
| 50 | Prabhat |
| 60 | Himanshi |
| 70 | Kanika |
mysql> select * from department;
| id | departmentName |
| 10 | Accounts |
| 20 | Development |
| 30 | QA |
| 40 | Designing |
mysql> select * from department_employee;
| departments_id | employees_employeeID |
| 20 | 50 |
| 20 | 60 |
| 30 | 50 |
| 30 | 40 |