Mybatis: 一对多(多对多)结果集

╰+攻爆jí腚メ 2022-05-23 11:20 225阅读 0赞

xml映射文件:

<?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="com.heiketu.testpackage.mapper.VendorsMapper">
    
        
        <resultMap id="manyToMany" type="com.heiketu.testpackage.pojo.Vendor">
            <id column="vend_id" property="vendId"/>
            <result column="vend_name" property="vendName"/>
            <result column="vend_address" property="vendAddress"/>
            <result column="vend_city" property="vendCity"/>
            <result column="vend_state" property="vendState"/>
            <result column="vend_zip" property="vendZip"/>
            <result column="vend_country" property="vendCountry"/>
    
            
            <collection property="productList" ofType="com.heiketu.testpackage.pojo.Product">
                <id column="prod_id" property="prodId"/>
                <result column="vend" property="vendId"/>
                <result column="prod_name" property="prodName"/>
                <result column="prod_desc" property="prodDesc"/>
            </collection>
        </resultMap>
    
        <select id="getResultManyToMany" resultMap="manyToMany">
          select
             v.*,
             p.prod_id,
             p.vend_id vend,
             p.prod_name prod_name,
             p.prod_desc prod_desc
          from Vendors v,Products p where v.vend_id = p.vend_id and v.vend_id = #{vendorId}
        </select>
    </mapper>

映射接口:

public interface VendorsMapper { 
        //数据一对多或多对多关系
        Vendor getResultManyToMany(@Param("vendorId") String vendorId);
    }

测试文件:

SqlSession sqlSession = null;
    try {
        String configFile = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(configFile);
        SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
        sqlSession = build.openSession();
    
        //以一对多的结果形式返回
        VendorsMapper mapper = sqlSession.getMapper(VendorsMapper.class);
        Vendor vendor = mapper.getResultManyToMany("FNG01");
        System.out.println(vendor);
    
    } catch (IOException e) {
        e.printStackTrace();
    }finally {
        sqlSession.close();
    }

结果:

Vendor{vendId='FNG01', vendName='Fun and Games', vendAddress='42 Galaxy Road', vendCity='London', vendState='null', vendZip='N16 6PS', vendCountry='England'}

**`mybatis获取结果集一对多或多对多，可以使用resultMap的collection。通过指定collection，获取对应的实体类的子结果集。`**

`collection`标签中需指定俩个属性: `property`属性指定对应的子结果集在实体类中的属性名,`ofType`属性指定每个子结果集的对象类型。