【Mybatis】多对多实例

①创建数据库和表，数据库为mytest，表为users、orders和users_orders

DROP TABLE IF EXISTS users;
CREATE TABLE users(
    id INT PRIMARY KEY auto_increment,
    name VARCHAR(20),
    age INT
);

INSERT INTO users(name, age) VALUES ('Jack', 40);
INSERT INTO users(name, age) VALUES ('Rose', 36);
INSERT INTO users(name, age) VALUES ('Tom', 18);

DROP TABLE IF EXISTS orders;
CREATE TABLE orders(
    order_id INT PRIMARY KEY auto_increment,
    order_name VARCHAR(20),
    order_price float
);

INSERT INTO orders(order_name, order_price) VALUES ('IPhone', 7777.77);
INSERT INTO orders(order_name, order_price) VALUES ('Haier', 8888.88);
INSERT INTO orders(order_name, order_price) VALUES ('Benz GLS', 9999);

DROP TABLE IF EXISTS users_orders;
CREATE TABLE users_orders(
    user_id INT,
    order_id INT
);

ALTER TABLE users_orders ADD CONSTRAINT fk_user_id FOREIGN KEY (user_id) REFERENCES users(id);
ALTER TABLE users_orders ADD CONSTRAINT fk_order_id FOREIGN KEY (order_id) REFERENCES orders(order_id);

INSERT INTO users_orders VALUES (1,1);
INSERT INTO users_orders VALUES (1,2);
INSERT INTO users_orders VALUES (1,3);
INSERT INTO users_orders VALUES (2,1);
INSERT INTO users_orders VALUES (2,3);
INSERT INTO users_orders VALUES (3,1);

②创建Java工程，导入相应的jar包

③创建配置文件conf.xml和数据库配置文件db.properties

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" 
    "http://mybatis.org/dtd/mybatis-3-config.dtd">
    
<configuration>
    <properties resource="db.properties"></properties>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${name}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    
    <mappers>
        <mapper resource="org/mybatis/mapping/userMapper.xml"/>
        <mapper resource="org/mybatis/mapping/orderMapper.xml"/>
    </mappers>
</configuration>

driver = com.mysql.jdbc.Driver
url = jdbc:mysql://localhost:3306/mytest
name = root
password = root

④创建实体类Users、Orders和Users_Orders

package org.mybatis.domain;

import java.util.Set;

public class Orders {
    private int order_id;
    private String order_name;
    private float order_price;
    private Set<Users> users;
    
    public int getOrder_id() {
        return order_id;
    }
    public void setOrder_id(int order_id) {
        this.order_id = order_id;
    }
    public String getOrder_name() {
        return order_name;
    }
    public void setOrder_name(String order_name) {
        this.order_name = order_name;
    }
    public float getOrder_price() {
        return order_price;
    }
    public void setOrder_price(float order_price) {
        this.order_price = order_price;
    }
    public Set<Users> getUsers() {
        return users;
    }
    public void setUsers(Set<Users> users) {
        this.users = users;
    }
    
    @Override
    public String toString() {
        return "Order [orderID:" + order_id + ", orderName:" + 
                order_name + ", orderPrice:" + order_price + "]";
    }
    
}

package org.mybatis.domain;

import java.util.Set;

public class Users {
    private int id;
    private String name;
    private int age;
    private Set<Orders> orders;
    
    public Set<Orders> getOrders() {
        return orders;
    }
    public void setOrders(Set<Orders> orders) {
        this.orders = orders;
    }
    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 getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    
    @Override
    public String toString() {
        return "User [userID:" + id + ", userName:" + 
                name + ", userAge:" + age + "]";
    }
    
}

package org.mybatis.domain;

public class Users_Orders {

    private Users user;
    private Orders order;
    
    public Users getUser() {
        return user;
    }
    public void setUser(Users user) {
        this.user = user;
    }
    public Orders getOrder() {
        return order;
    }
    public void setOrder(Orders order) {
        this.order = order;
    }
    
    
}

⑤创建sql映射文件userMapper.xml和orderMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    
<mapper namespace="org.mybatis.mapping.userMapper">
    <select id="getUsers" resultMap="getUsersMap">
        select * from users u, orders o, users_orders uo
        where u.id=uo.user_id and o.order_id=uo.order_id
        and u.id=#{id}
    </select>
    
    <resultMap type="org.mybatis.domain.Users" id="getUsersMap">
        <id column="id" property="id" />
        <result column="name" property="name" />
        <result column="age" property="age"/>
        <collection property="orders" ofType="org.mybatis.domain.Orders">
            <id column="order_id" property="order_id"/>
            <result column="order_name" property="order_name"/>
            <result column="order_price" property="order_price"/>
        </collection>
    </resultMap>
</mapper>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    
<mapper namespace="org.mybatis.mapping.orderMapper">
    <select id="getOrders" resultMap="getOrdersMap">
        select * from users u, orders o, users_orders uo
        where u.id=uo.user_id and o.order_id=uo.order_id
        and o.order_id=#{id}
    </select>
    
    <resultMap type="org.mybatis.domain.Orders" id="getOrdersMap">
        <id column="order_id" property="order_id" />
        <result column="order_name" property="order_name" />
        <result column="order_price" property="order_price"/>
        <collection property="users" ofType="org.mybatis.domain.Users">
            <id column="id" property="id"/>
            <result column="name" property="name"/>
            <result column="age" property="age"/>
        </collection>
    </resultMap>
</mapper>

⑥向配置文件中注册 userMapper.xml和orderMapper.xml 文件【已添加，查看第③步】

 ⑦测试类

package org.mybatis.app;

import java.io.InputStream;
import java.util.List;
import java.util.Set;

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import org.mybatis.domain.Orders;
import org.mybatis.domain.Users;

public class TestManyToMany {

    SqlSession session;
    
    @Before
    public void beforeLoad() {
        InputStream inputStream = 
                TestManyToMany.class.getClassLoader().getResourceAsStream("conf.xml");
        SqlSessionFactory sqlSessionFactory = 
                new SqlSessionFactoryBuilder().build(inputStream);
        session = sqlSessionFactory.openSession();
    }
    
    @Test
    public void testGetUsers() {
        String statement = "org.mybatis.mapping.userMapper.getUsers";
        List<Users> usersList = session.selectList(statement, 2);
        for(Users user : usersList) {
            System.out.println(user.getName() + "买了" + user.getOrders().size() + "个产品, 它们是:");
            Set<Orders> orders = user.getOrders();
            for(Orders order : orders) {
                System.out.println(order.getOrder_name());
            }
        }
    }
    
    @Test
    public void testGetOrders() {
        String statement = "org.mybatis.mapping.orderMapper.getOrders";
        List<Orders> orderList = session.selectList(statement, 3);
        for(Orders order : orderList) {
            System.out.println(order.getOrder_name() + "被买了" + order.getUsers().size() + "次, 买它的人有:");
            Set<Users> users = order.getUsers();
            for(Users user : users) {
                System.out.println(user.getName());
            }
        }
    }
    
}

⑧结构图：