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); } }