Mybatis|Mybatis一对多实战 mysql|一对多|表|Mybatis

文章图片

文章图片

左表为user，右表为orders，一对多的关系
实体类

package cn.itcast.mybatis.pojo; import java.util.Date; import java.util.List; public class User{ private int id; private String username; private String sex; private Date birthday; private String address; private List orders; //此处存的为多的一方的集合}

package cn.itcast.mybatis.pojo; import java.util.Date; public class Orders { private int id; private int user_id; private String number; private Date createtime; private String note; }

user对应的dao接口

package cn.itcast.mybatis.mapper; import cn.itcast.mybatis.pojo.User; import java.util.List; public interface UserMapper { public List testOneToMany(); }

user对应的mapper.xml

select u.id,u.username,u.address,o.id oid,o.user_id,o.number,o.createtime from user u left join orders o on u.id = o.user_id

测试类

package cn.itcast.mybatis.quickstart; import cn.itcast.mybatis.mapper.UserMapper; import cn.itcast.mybatis.pojo.User; 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 org.junit.Test; import java.io.IOException; import java.io.InputStream; import java.util.ArrayList; import java.util.Date; import java.util.List; /** * mybatis入门程序 * @author Ming Wang * */ public class QuickStartDemo { /** * 获取mybatis回话SqlSession * @return * @throws IOException */ private SqlSession getSqlSession() throws IOException { // 1、创建SqlSessionFactoryBuilder加载mybatis的核心配置文件 SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder(); // 2、获取回话工厂SqlSessionFactory String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream); // 3、获取回话SqlSession SqlSession sqlSession = sqlSessionFactory.openSession(); return sqlSession; }@Test public void testOneToMany() throws IOException { SqlSession sqlSession = getSqlSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); List users = mapper.testOneToMany(); System.out.println(users); sqlSession.close(); } }

【Mybatis|Mybatis一对多实战】得到的结果-->第二行和第三行为user对应的的二个orders

[User{id=1, username='王五', sex='null', birthday=null, address='null',

orders=[Orders{id=3, user_id=1, number='1000010', createtime=Wed Feb 04 13:22:35 CST 2015, note='null'},

Orders{id=4, user_id=1, number='1000011', createtime=Tue Feb 03 13:22:41 CST 2015, note='null'}]},

User{id=10, username='张三', sex='null', birthday=null, address='北京市', orders=[Orders{id=5, user_id=10, number='1000012', createtime=Thu Feb 12 16:13:23 CST 2015, note='null'}]}, User{id=16, username='张小明', sex='null', birthday=null, address='河南郑州', orders=[]}, User{id=22, username='陈小明', sex='null', birthday=null, address='河南郑州', orders=[]}, User{id=24, username='张三丰', sex='null', birthday=null, address='河南郑州', orders=[]}, User{id=25, username='陈小明', sex='null', birthday=null, address='河南郑州', orders=[]}, User{id=26, username='王五', sex='null', birthday=null, address='null', orders=[]}, User{id=27, username='1', sex='null', birthday=null, address='2', orders=[]}, User{id=28, username='1', sex='null', birthday=null, address='2', orders=[]}, User{id=29, username='lilili', sex='null', birthday=null, address='SHHHH', orders=[]}, User{id=31, username='q', sex='null', birthday=null, address='q', orders=[]}, User{id=32, username='1', sex='null', birthday=null, address='2', orders=[]}]

数据库查询出来的结果