使用注解方式实现MyBatis高级映射（一对多)

实验步骤

背景描述：一个省拥有很多个城市。
项目结构：

1.创建实体类

城市

@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class City {
    private Integer cid;
    private String cname;
    private Integer person;
    private Integer pid;
}

省份

@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Province {
	
	private Integer pid;
	private String pname;

	/*在你的省份中有对应的城市----城市不重复；*/
	private Set<City> Cities;

}

2.创建mapper接口

从表接口：

public interface CityDao {
    //根据省份id查找城市
    @Select("select * from city where pid=#{pid}")
    List<City> getCityById(Integer pid) throws Exception;

}

主表接口：

public interface ProvinceDao {
    //根据省份id查找城市
    @Select("select * from province where pid=#{pid}")
    @Results({
            @Result(id = true, column = "pid", property = "pid"),
            @Result(column = "pname", property = "pname"),
            @Result(column = "pid",property="Cities",
            //一对多映射
            many = @Many(select = "com.rg1.mapper.CityDao.getCityById", fetchType = FetchType.EAGER
            )),
    })
    Province getProvinceById(Integer pid) throws Exception;
}

3.全局配置文件config.xml

<?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="jdbc.properties"></properties>
    <environments default="dev">
        <environment id="dev">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}" />
                <property name="url" value="${jdbc.url}" />
                <property name="username" value="${jdbc.username}" />
                <property name="password" value="${jdbc.password}" />
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper class="com.rg1.mapper.CityDao"></mapper>
        <mapper class="com.rg1.mapper.ProvinceDao"></mapper>
    </mappers>
</configuration>

4.测试

public class Test1 {
    public static void main(String[] args) throws Exception {
        InputStream inputstream = Resources.getResourceAsStream("config.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputstream);
        SqlSession session = sqlSessionFactory.openSession(true);
        System.out.println(session);
        ProvinceDao mapper = session.getMapper(ProvinceDao.class);
        Province province = mapper.getProvinceById(1);
        System.out.println(province.getPname());
        Set<City> cities = province.getCities();
        for(City c:cities){
            System.out.println("---"+c.getCname());
        }
    }
}

运行截图：