hibernate--关联关系的CRUD

逃离我推掉我的手 2024-02-18 14:51 68阅读 0赞

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多对一单向关联：

Group.java:

package com.bean;
    
    import java.util.HashSet;
    import java.util.Set;
    
    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    import javax.persistence.OneToMany;
    import javax.persistence.Table;
    
    @Entity
    @Table(name="t_group")
    public class Group {
    	private int id;
    	private String name;
    
    	@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;
    	}
    
    }

User.java:

package com.bean;
    
    import javax.persistence.CascadeType;
    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    import javax.persistence.ManyToOne;
    import javax.persistence.OneToMany;
    import javax.persistence.Table;
    
    import org.hibernate.annotations.Cascade;
    
    @Entity
    @Table(name="t_user")
    public class User {
    	private int id;
    	private String name;
    	private Group group;	
    
    	@ManyToOne(cascade={CascadeType.ALL})    //cascade---级联操作
    	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;
    	}
    
    }

hibernate.cfg.xml:

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE hibernate-configuration PUBLIC
            "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
            "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
    <hibernate-configuration>
       <session-factory>
         <property name="connection.driver_class">com.mysql.jdbc.Driver</property>    
         <property name="connection.url">jdbc:mysql://localhost:3306/user</property>     
         <property name="connection.username">root</property>   
         <property name="connection.password">root</property>
         
         <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
         <property name="show_sql">true</property>
         
         <property name="hbm2ddl.auto">update</property>
         <property name="show_sql">true</property>
         <property name="format_sql">true</property>  
         
         <property name="current_session_context_class">thread</property>
          <mapping class="com.bean.Group"/>
         <mapping class="com.bean.User"/>  
       
       </session-factory>
    </hibernate-configuration>

测试：

package com.test;
    
    import org.hibernate.Query;
    import org.hibernate.Session;
    import org.hibernate.SessionFactory;
    import org.hibernate.cfg.AnnotationConfiguration;
    import org.hibernate.cfg.Configuration;
    import org.hibernate.service.ServiceRegistryBuilder;
    import org.hibernate.tool.hbm2ddl.SchemaExport;
    
    import com.bean.Group;
    import com.bean.User;
    import com.bean.User2;
    
    public class Test_W_H {
      public static void main(String []args) {
    	   Configuration cfg = new Configuration();
    	   cfg.configure(); //加载hibernate配置文件
    	   SessionFactory sessionFactory = cfg.buildSessionFactory(new ServiceRegistryBuilder().applySettings(cfg.getProperties()).buildServiceRegistry());	   
    	   Session session = sessionFactory.getCurrentSession();
    
    	   session.beginTransaction();  //开启事务
    	   
    	   User user = new User();
    	   user.setName("代里");
    	   
    	   Group group = new Group();
    	   group.setName("team1");
    	   user.setGroup(group);
    	   session.save(user);
    	   session.getTransaction().commit(); // 事务提交
    	   System.out.println("the end");
    }
    }

![Center][]

![Center 1][]  
  
  
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一对多双向关联：

在Group.java增加属性：

private Set<User> users = new HashSet<User>();
    
    	@OneToMany(mappedBy="group",
    			cascade={CascadeType.ALL}
    	             )
    	public Set<User> getUsers() {
    		return users;
    	}
    
    	public void setUsers(Set<User> users) {
    		this.users = users;
    	}

测试：

session.beginTransaction();  //开启事务
    	   
    	   User user1 = new User();
    	   user1.setName("代里");
    	   User user2 = new User();
    	   user2.setName("张三");
    	   
    	   Group group = new Group();
    	   group.setName("team1");
    	   group.getUsers().add(user1);
    	   group.getUsers().add(user2);
    	   user1.setGroup(group);
    	   user2.setGroup(group);  
    	   session.save(group);
    	   session.getTransaction().commit(); // 事务提交

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read读取：

OneToMany:需要配置fetch：(fetch默认状态为lazy)

@OneToMany(mappedBy="group",
    			cascade={CascadeType.ALL},
    			fetch=FetchType.EAGER
    	             )

ManyToOne则不需要配置，因为fetch默认状态为eager

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级联删除（防止级联删除效应）：

1、取消级联关系

User user = (User)session.get(User.class, 7);   
    	   user.setGroup(null);
    	   session.delete(user);
    	   session.getTransaction().commit(); // 事务提交

2、设置Hql来控制。

session.createQuery("delete from User u where u.id = 8").executeUpdate();

[Center]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/38e626517714440a9fb3550a5c16519e.png
[Center 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/5005d59f6e3e4192ae841774f88251f2.png