hibernate--多对一（一对多）单向外键关联

一时失言乱红尘 2024-02-18 14:49 34阅读 0赞

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多对一

一、通过annotation注解:

Group.java:

package com.bean;
    
    import javax.persistence.Entity;
    import javax.persistence.Id;
    import javax.persistence.Table;
    
    @Entity
    @Table(name="t_group")
    public class Group {
    	private int id;
    	private String name;
    
    	@Id
    	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.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    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;
    
    	@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;
    	}
    
    	@ManyToOne
    	@JoinColumn(name="groupId")
    	public Group getGroup() {
    		return group;
    	}
    
    	public void setGroup(Group group) {
    		this.group = group;
    	}
    
    }

cfg.xml配置：

<?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>

二、通过XML配置：

User.hbm.xml:

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE hibernate-mapping PUBLIC
            "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
            "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    <hibernate-mapping>
      <class name = "com.bean.User" table = "t_user" >
    
         <id name = "id" column="id">
           <generator class="native"/>
         </id>
         <property name="name" />
         <many-to-one name="group" column="groupId"/>
      </class>
    </hibernate-mapping>

Group.hbm.xml:

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE hibernate-mapping PUBLIC
            "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
            "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    <hibernate-mapping>
      <class name = "com.bean.Group" table = "t_group" >
    
         <id name = "id" column="id">
           <generator class="native"/>
         </id>
         <property name="name" />
      </class>
    </hibernate-mapping>

cfg.xml文件中修改映射配置：

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一对多

一：annotation注解：

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;
    	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
    	@JoinColumn(name="groupId")
    	public Set<User> getUsers() {
    		return users;
    	}
    
    	public void setUsers(Set<User> users) {
    		this.users = users;
    	}
    
    }

User.java:

package com.bean;
    
    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;
    
    @Entity
    @Table(name="t_user")
    public class User {
    	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;
    	}
    
    }

二：XML配置：

Group.hbm.xml配置：

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一对多双向关联和多对一双向关联是没有区别的，通常说成一对多双向关联。将一对多和多对一单向关联综合起来就是一对多双向关联。

在映射一对多的双向关联关系时，应该在“one”方把<set>元素的inverse属性设为true，这样可以提高应用的性能。inverse="false" 为主控方，inverse="true"为被控方