Java学习之MyBatis（3）

收获满满的一天啊，接下来是一个多对多的关系查询，多对多也就是一对多的进化版。

1.先在数据库弄几个表

这是在数据库新建的三个表
顾客表：
商品表：
顾客_商品表（用来连接两张表之间的关系的,cid gid 都是外键）：

2.然后开始动手：

贴上文件目录（越来越长了）：

首先还是先创建实体类

Customer类：

package com.southwind.entity;

import lombok.Data;

import java.util.List;

@Data
public class Customer {
    private int id ;
    private String name;
    private List<Goods> goods;
}

Goods类

package com.southwind.entity;

import lombok.Data;

import java.util.List;

@Data
public class Goods {
    private int id;
    private String name;
    private List<Customer> customers;
}

然后开始操作：

1.先是利用顾客id查询购买的商品，

先写 CustomerRepository接口

package com.southwind.repository;

import com.southwind.entity.Customer;

public interface CustomerRepository {
    public Customer findById(int id);
}

然后是CustomerRepositoryMapper.xml
文件

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.southwind.repository.CustomerRepository">
<!--    多对多的查询 -->
    <select id="findById" parameterType="int" resultMap="customerMap">
        select c.id cid,c.name cname,g.id gid,g.name gname
        from customer as c,goods as g,customer_goods as cg
        where c.id = #{id} and c.id = cg.cid and g.id = cg.gid
    </select>
    <resultMap id="customerMap" type="com.southwind.entity.Customer">
        <id column="cid" property="id"></id>
        <result column="cname" property="name"></result>
        <collection property="goods" ofType="com.southwind.entity.Goods">
            <id column="gid" property="id"/>
            <result column="gname" property="name"/>
        </collection>
    </resultMap>
</mapper>

测试类Test_5:

package com.southwind.test;

import com.southwind.repository.CustomerRepository;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.InputStream;

public class Test_5 {
    public static void main(String[] args) {
        //        加载配置文件
        InputStream inputStream = Test.class.getClassLoader().getResourceAsStream("config.xml");
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        CustomerRepository customerRepository = sqlSession.getMapper(CustomerRepository.class);
        System.out.println(customerRepository.findById(1));
        sqlSession.close();
    }
}

贴个查询结果图出来

2.既然有了顾客查询商品，那应该也有商品查询顾客。

GoodsRepository 接口

package com.southwind.repository;

import com.southwind.entity.Goods;

public interface GoodsRepository {
    public Goods findById(int id);
}

GoodsRepositoryMapper.xml

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.southwind.repository.GoodsRepository">
    <!--    多对多的关系查询 -->
    <select id="findById" parameterType="int" resultMap="goodsMap">
        select c.id cid,c.name cname,g.id gid,g.name gname
        from customer as c,goods as g,customer_goods as cg
        where g.id = #{id} and c.id = cg.cid and g.id = cg.gid
    </select>
    <resultMap id="goodsMap" type="com.southwind.entity.Goods">
        <id column="gid" property="id"></id>
        <result column="gname" property="name"></result>
        <collection property="customers" ofType="com.southwind.entity.Customer">
            <id column="cid" property="id"/>
            <result column="cname" property="name"/>
        </collection>
    </resultMap>
</mapper>

来个Test_6测试类

package com.southwind.test;

import com.southwind.repository.GoodsRepository;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.InputStream;

public class Test_6 {
    public static void main(String[] args) {
        InputStream inputStream = Test.class.getClassLoader().getResourceAsStream("config.xml");
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        GoodsRepository goodsRepository = sqlSession.getMapper(GoodsRepository.class);
        System.out.println(goodsRepository.findById(3));
        sqlSession.close();
    }
}