hibernate_1700_one2many_many2one_bi_crud

这是一个hibernate 多对一 一对多  基于外键双向关联


package com.bit.hibernate;

import java.util.HashSet;
import java.util.Set;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name="t_group")
public class Group {
private int id;
private String name;
private Set<User> users = new HashSet<User>();
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@OneToMany(mappedBy="group"
)

public Set<User> getUsers() {
return users;
}
public void setUsers(Set<User> users) {
this.users = users;
}
}


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package com.bit.hibernate;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name="t_user")
public class User {
private int id;
private String name;
private Group group;
@ManyToOne(cascade={CascadeType.ALL})
public Group getGroup() {
return group;
}
public void setGroup(Group group) {
this.group = group;
}
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}

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package com.bit.hibernate;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;

public class Main {

/**
* @param args
*/
public static void main(String[] args) {

SessionFactory sessionFactory = new  AnnotationConfiguration().configure().buildSessionFactory();

User user = new User();
    user.setName("u1");
    Group group = new Group();
    group.setName("g1");
group.getUsers().add(user);
user.setGroup(group);
Session session = sessionFactory.getCurrentSession();

session.beginTransaction();
session.save(user);
session.getTransaction().commit();

}

}

双向关联必设mappedBy  外键加到多的一方  还有一个cascade叫级联 也就是说在保存user的时候 自动保存了相应的group