MyBatis实现多对多

喜欢ヅ旅行 2022-04-14 03:37 152阅读 0赞

**第一步：导入两个jar包分别为mybatis-3.2.3.jar和mysql-connector-java-5.1.25-bin.jar，如下图所示：**  
![在这里插入图片描述][2018112318561019.jpg]  
**第二步创建三张表（本人三张表分别为user、groups和usergroup），如下图所示：**  
user表  
![在这里插入图片描述][20181123190147649.jpg]  
groups表  
![在这里插入图片描述][20181123185828704.jpg]  
usergroup表  
![在这里插入图片描述][20181123190224937.jpg]  
**第三步：创建改表相对应的实体类：**  
推荐类与数据库中的表名同名（类命名规范：类名首字母大写）  
User类：

package com.zhiyuan.Bean;
    
    import java.util.List;
    
    public class User {
    	private int id;
    	private String name;
    	private int phone;
    	private List<Groups> group;//用来接收Groups表中的多条数据
    	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;
    	}
    	public int getPhone() {
    		return phone;
    	}
    	public void setPhone(int phone) {
    		this.phone = phone;
    	}
    	public List<Groups> getGroup() {
    		return group;
    	}
    	public void setGroup(List<Groups> group) {
    		this.group = group;
    	}
    	
    }

Groups类：

package com.zhiyuan.Bean;
    
    import java.util.List;
    
    public class Groups {
    	private int id;
    	private String group;
    	private List<User> user;//用来接收User表中的多条数据
    	public int getId() {
    		return id;
    	}
    	public void setId(int id) {
    		this.id = id;
    	}
    	public String getGroup() {
    		return group;
    	}
    	public void setGroup(String group) {
    		this.group = group;
    	}
    	public List<User> getUser() {
    		return user;
    	}
    	public void setUser(List<User> user) {
    		this.user = user;
    	}
    	
    }

UserGroup类

package com.zhiyuan.Bean;
    
    public class UserGroup {
    	private int u_id;
    	private int g_id;
    	public int getU_id() {
    		return u_id;
    	}
    	public void setU_id(int u_id) {
    		this.u_id = u_id;
    	}
    	public int getG_id() {
    		return g_id;
    	}
    	public void setG_id(int g_id) {
    		this.g_id = g_id;
    	}
    	
    }

**第四步：创建好实体映射文件**  
group.xml

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE mapper PUBLIC "mybatis-3-mapper" "mybatis-3-mapper.dtd" >
    <mapper namespace="com.zhiyuan.Dao.UserGroupMap">
    	<resultMap type="Groups" id="MyMap_1">
    		<result property="id" column="id"/>
    		<result property="group" column="group"/>
    		<collection property="user" column="id" select="com.zhiyuan.Dao.GetUserGroupID" />
    		
    	</resultMap>
    
    	<select id="GetGroupID" parameterType="String" resultMap="MyMap_1">
    		select * from groups where groups.group=#{group}
    	</select>
    </mapper>

usergroup.xml

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE mapper PUBLIC "mybatis-3-mapper" "mybatis-3-mapper.dtd" >
    <mapper namespace="com.zhiyuan.Dao">
    	<resultMap type="User" id="MyMap_2">
    		<result property="id" column="id"/>
    		<result property="name" column="name"/>
    		<result property="phone" column="phone"/>
    	</resultMap>
    
    	<select id="GetUserGroupID" parameterType="int" resultMap="MyMap_2">
    		select * from user,usergroup where user.id=usergroup.u_id and usergroup.u_id=#{id}
    	</select>
    </mapper>

**第五步：创建接口**  
UserGroupMap.java接口

package com.zhiyuan.Dao;
    
    import com.zhiyuan.Bean.Groups;
    
    public interface UserGroupMap {
    	public Groups GetGroupID(String group);
    	//该方法用来向group.xml中的SQL语句传值，方法名需与group.xml中的select泛型中的id值保持一致
    }

第六步：创建好MaBatis的主配置文件  
config.xml

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE configuration PUBLIC "mybatis-3-config" "mybatis-3-config.dtd" >
    <configuration>
    	<typeAliases>
    		<package name="com.zhiyuan.Bean"/>
    	</typeAliases>
    	
    	<environments default="development">
    		<environment id="development">
    			<transactionManager type="JDBC"></transactionManager>
    			<dataSource type="POOLED">
    				<property name="driver" value="com.mysql.jdbc.Driver"/>
    				<property name="url" value="jdbc:mysql://localhost:3306/数据库名"/>
    				<property name="username" value="用户名"/>
    				<property name="password" value="密码"/>
    			</dataSource>
    		</environment>
    	</environments>
    	
    	<mappers>
    		<mapper resource="com/zhiyuan/Dao/group.xml"/>
    		<mapper resource="com/zhiyuan/Dao/usergroup.xml"/>
    	</mappers>
    </configuration>

**第七步：编译测试类**  
Text测试类

package com.zhiyuan.Text;
    
    import java.io.IOException;
    import java.io.Reader;
    import java.util.List;
    
    import org.apache.ibatis.io.Resources;
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    
    import com.zhiyuan.Bean.Groups;
    import com.zhiyuan.Bean.User;
    import com.zhiyuan.Dao.UserGroupMap;
    
    public class Text {
    
    	public static void main(String[] args) throws IOException {
    		Reader reader = Resources.getResourceAsReader("config.xml");
    		//通过Resources类调用getResourceAsReader方法来获取 config主配置文件并用Reader来进行接收
    		SqlSessionFactory session = new SqlSessionFactoryBuilder().build(reader);
    		//得到sqlsession工厂对象，通过new一个sqlsessionfactorybuild调用build方法获得一个sqlsessionfacory对象
    		SqlSession sql = session.openSession();
    		//openSession用来创建Sqlsession
    		UserGroupMap usergroupmap = sql.getMapper(UserGroupMap.class);
    		//通过session对象调用getmapper方法得到接口的实例
    		Groups group = usergroupmap.GetGroupID("A组");
    		//通过接口对象调用里面的方法并传值
    		System.out.println(group.getGroup());
    		List<User> list = group.getUser();
    		//通过list集合来接收多条数据
    		for (User user : list) {
    			//用加强for循环将结果打印出来
    			System.out.println(user.getName());
    		}
    	}
    
    }

**运行结果**  
![在这里插入图片描述][20181124090939326.jpg]

[2018112318561019.jpg]: /images/20220414/3918673dad3c4fbba120e1acd5a583f3.png
[20181123190147649.jpg]: /images/20220414/408f40680b4e4c27bca154a873c4e7d5.png
[20181123185828704.jpg]: /images/20220414/c637a32286ce4eb4b635a23bc1b10bdf.png
[20181123190224937.jpg]: /images/20220414/7a7cb4df2c694427823ba99aa950183e.png
[20181124090939326.jpg]: /images/20220414/05a8e74aec4c458f9a0c591fef709d54.png