Mybatis高级映射多对一映射映射关系解析-----Mybatis框架

野性酷女 2024-03-03 03:28 16阅读 0赞

>     多对一映射(主表和附表)
>     Mapping映射到JVM中得到两个对象
>     多个的我们称为主表(一的那个作为多个的属性property存在)
>     谁是主表,多对一,多是主表,一对多,一在前,一是主表
>     如果主表是t_student,那么JVM的主对象就是Student对象
>     内存结构中就会据此生成student的成员变量clazz对象(通过这个引用就找到了这个对象)
>     反过来如果是研究一对多,那么就是clazz类的对象实例中有一个List<Student>,通过student的cid进行关联
> 
>     多对一映射(主表和附表)
>     Mapping映射到JVM中得到两个对象
>     多个的我们称为主表(一的那个作为多个的属性property存在)
>     谁是主表,多对一,多是主表,一对多,一在前,一是主表
>     如果主表是t_student,那么JVM的主对象就是Student对象
>     内存结构中就会据此生成student的成员变量clazz对象(通过这个引用就找到了这个对象)
>     反过来如果是研究一对多,那么就是clazz类的对象实例中有一个List<Student>,通过student的cid进行关联

>     <?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.powernode.mybatis.mappers.StudentMapper">
>         <resultMap id="studentResultMap" type="student">
>             <id property="sid" column="sid"></id>
>             <result property="sname" column="sname"></result>
>             <result property="clazz.cid" column="cid"></result>
>             <result property="clazz.cname" column="cname"></result>
>         </resultMap>
>         <select id="selectById" resultMap="studentResultMap">
>             select
>                 s.sid,s.sname,c.cid,c.cname
>             from
>                 t_stu as s left join t_clazz as c on s.cid = c.cid
>             where
>                 s.sid = #{sid};
>         </select>
>     </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="com.powernode.mybatis.mappers.StudentMapper">
>         <resultMap id="studentResultMap" type="student">
>             <id property="sid" column="sid"></id>
>             <result property="sname" column="sname"></result>
>             <result property="clazz.cid" column="cid"></result>
>             <result property="clazz.cname" column="cname"></result>
>         </resultMap>
>         <select id="selectById" resultMap="studentResultMap">
>             select
>                 s.sid,s.sname,c.cid,c.cname
>             from
>                 t_stu as s left join t_clazz as c on s.cid = c.cid
>             where
>                 s.sid = #{sid};
>         </select>
>     </mapper>

>     package com.powernode.mybatis.mappers;
>     
>     import com.powernode.mybatis.pojo.Student;
>     
>     public interface StudentMapper
>     {
>         //根据ID获取学生信息,获取学生关联的ID信息
>         Student selectById(Integer id);
>     }
> 
>     package com.powernode.mybatis.mappers;
>     
>     import com.powernode.mybatis.pojo.Student;
>     
>     public interface StudentMapper
>     {
>         //根据ID获取学生信息,获取学生关联的ID信息
>         Student selectById(Integer id);
>     }

>     package com.powernode.mybatis.Test;
>     
>     import com.powernode.mybatis.mappers.StudentMapper;
>     import com.powernode.mybatis.pojo.Student;
>     import com.powernode.mybatis.utils.SqlSessionUtils;
>     import org.apache.ibatis.session.SqlSession;
>     import org.junit.Test;
>     import org.slf4j.Logger;
>     import org.slf4j.LoggerFactory;
>     
>     public class StudentMapperTest
>     {
>         private static final Logger logger = LoggerFactory.getLogger(StudentMapperTest.class);
>         @Test
>         public void selectById()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
>             Student student = mapper.selectById(1);
>             logger.info(student.toString());
>             SqlSessionUtils.close(sqlSession);
>         }
>     }
> 
>     package com.powernode.mybatis.Test;
>     
>     import com.powernode.mybatis.mappers.StudentMapper;
>     import com.powernode.mybatis.pojo.Student;
>     import com.powernode.mybatis.utils.SqlSessionUtils;
>     import org.apache.ibatis.session.SqlSession;
>     import org.junit.Test;
>     import org.slf4j.Logger;
>     import org.slf4j.LoggerFactory;
>     
>     public class StudentMapperTest
>     {
>         private static final Logger logger = LoggerFactory.getLogger(StudentMapperTest.class);
>         @Test
>         public void selectById()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
>             Student student = mapper.selectById(1);
>             logger.info(student.toString());
>             SqlSessionUtils.close(sqlSession);
>         }
>     }