Mybatis一对多关系映射实现的方法-----Mybatis框架

ゝ一世哀愁。 2024-03-03 08:56 124阅读 0赞

>     一个班级对象对应多个学生对象
>     根据我们的班级编号查询班级下所有的学生
>     一条clazz表就对应了一个clazz对象,这些对象和我们的学生对象产生关系
>     怎么表示这一个班级对应多少个学生对象
>     集合或者数组都可以容纳多个元素
>     List<Student>
> 
>     一个班级对象对应多个学生对象
>     根据我们的班级编号查询班级下所有的学生
>     一条clazz表就对应了一个clazz对象,这些对象和我们的学生对象产生关系
>     怎么表示这一个班级对应多少个学生对象
>     集合或者数组都可以容纳多个元素
>     List<Student>

>     <?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.ClazzMapper">
>         <select id="selectByIdStepTwo" resultType="clazz">
>             select cid,cname from t_clazz where cid = #{cid}
>         </select>
>         <select id="selectByCollection" resultMap="clazzResultMap">
>             select c.cid,c.cname,s.sid,s.sname from t_clazz as c left join t_stu as s on c.cid = s.cid where c.cid = #{cid}
>         </select>
>         <resultMap id="clazzResultMap" type="Clazz">
>             <id property="cid" column="cid"></id>
>             <result property="cname" column="cname"></result>
>     
>             <collection property="studentList" ofType="student">
>                 <id property="sid" column="sid"></id>
>                 <result property="sname" column="sname"></result>
>             </collection>
>         </resultMap>
>     </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.ClazzMapper">
>         <select id="selectByIdStepTwo" resultType="clazz">
>             select cid,cname from t_clazz where cid = #{cid}
>         </select>
>         <select id="selectByCollection" resultMap="clazzResultMap">
>             select c.cid,c.cname,s.sid,s.sname from t_clazz as c left join t_stu as s on c.cid = s.cid where c.cid = #{cid}
>         </select>
>         <resultMap id="clazzResultMap" type="Clazz">
>             <id property="cid" column="cid"></id>
>             <result property="cname" column="cname"></result>
>     
>             <collection property="studentList" ofType="student">
>                 <id property="sid" column="sid"></id>
>                 <result property="sname" column="sname"></result>
>             </collection>
>         </resultMap>
>     </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="studentResultMapAssociation" type="student">
>             <id property="sid" column="sid"></id>
>             <result property="sname" column="sname"></result>
>     
>     
>             <association property="clazz" javaType="clazz">
>                 <id column="cid" property="cid"></id>
>                 <result property="cname" column="cname"></result>
>             </association>
>         </resultMap>
>         <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>
>         <select id="selectByAssociation" resultMap="studentResultMapAssociation">
>             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>
>         <select id="selectByIDStepOne" resultMap="studentResultMapByStep">
>             select sid,sname,cid from t_stu where sid = #{sid}
>         </select>
>     
>     
>     
>         <resultMap id="studentResultMapByStep" type="student">
>             <id property="sid" column="sid"></id>
>             <result property="sname" column="sname"></result>
>     
>     
>             <association property="clazz"
>                          select="com.powernode.mybatis.mappers.ClazzMapper.selectByIdStepTwo"
>                          fetchType="eager"
>                          column="cid"></association>
>         </resultMap>
>     </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="studentResultMapAssociation" type="student">
>             <id property="sid" column="sid"></id>
>             <result property="sname" column="sname"></result>
>     
>     
>             <association property="clazz" javaType="clazz">
>                 <id column="cid" property="cid"></id>
>                 <result property="cname" column="cname"></result>
>             </association>
>         </resultMap>
>         <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>
>         <select id="selectByAssociation" resultMap="studentResultMapAssociation">
>             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>
>         <select id="selectByIDStepOne" resultMap="studentResultMapByStep">
>             select sid,sname,cid from t_stu where sid = #{sid}
>         </select>
>     
>     
>     
>         <resultMap id="studentResultMapByStep" type="student">
>             <id property="sid" column="sid"></id>
>             <result property="sname" column="sname"></result>
>     
>     
>             <association property="clazz"
>                          select="com.powernode.mybatis.mappers.ClazzMapper.selectByIdStepTwo"
>                          fetchType="eager"
>                          column="cid"></association>
>         </resultMap>
>     </mapper>

>     package com.powernode.mybatis.mappers;
>     
>     import com.powernode.mybatis.pojo.Clazz;
>     
>     public interface ClazzMapper
>     {
>         //分步查询第二步,根据cid查询班级信息
>         Clazz selectByIdStepTwo(Integer cid);
>         Clazz selectByCollection(Integer cid);
>     }
> 
>     package com.powernode.mybatis.mappers;
>     
>     import com.powernode.mybatis.pojo.Clazz;
>     
>     public interface ClazzMapper
>     {
>         //分步查询第二步,根据cid查询班级信息
>         Clazz selectByIdStepTwo(Integer cid);
>         Clazz selectByCollection(Integer cid);
>     }

>     package com.powernode.mybatis.pojo;
>     
>     import java.util.List;
>     
>     public class Clazz
>     {
>         private Integer cid;
>         private String cname;
>         private List<Student> studentList;
>     
>         @Override
>         public String toString() {
>             return "Clazz{" +
>                     "cid=" + cid +
>                     ", cname='" + cname + '\'' +
>                     ", studentList=" + studentList +
>                     '}';
>         }
>     
>         public List<Student> getStudentList() {
>             return studentList;
>         }
>     
>         public void setStudentList(List<Student> studentList) {
>             this.studentList = studentList;
>         }
>     
>         public Integer getCid() {
>             return cid;
>         }
>     
>         public void setCid(Integer cid) {
>             this.cid = cid;
>         }
>     
>         public String getCname() {
>             return cname;
>         }
>     
>         public void setCname(String cname) {
>             this.cname = cname;
>         }
>     
>         public Clazz() {
>         }
>     
>         public Clazz(Integer cid, String cname) {
>             this.cid = cid;
>             this.cname = cname;
>         }
>     }
> 
>     package com.powernode.mybatis.pojo;
>     
>     import java.util.List;
>     
>     public class Clazz
>     {
>         private Integer cid;
>         private String cname;
>         private List<Student> studentList;
>     
>         @Override
>         public String toString() {
>             return "Clazz{" +
>                     "cid=" + cid +
>                     ", cname='" + cname + '\'' +
>                     ", studentList=" + studentList +
>                     '}';
>         }
>     
>         public List<Student> getStudentList() {
>             return studentList;
>         }
>     
>         public void setStudentList(List<Student> studentList) {
>             this.studentList = studentList;
>         }
>     
>         public Integer getCid() {
>             return cid;
>         }
>     
>         public void setCid(Integer cid) {
>             this.cid = cid;
>         }
>     
>         public String getCname() {
>             return cname;
>         }
>     
>         public void setCname(String cname) {
>             this.cname = cname;
>         }
>     
>         public Clazz() {
>         }
>     
>         public Clazz(Integer cid, String cname) {
>             this.cid = cid;
>             this.cname = cname;
>         }
>     }

>     package com.powernode.mybatis.Test;
>     
>     import com.powernode.mybatis.mappers.ClazzMapper;
>     import com.powernode.mybatis.mappers.StudentMapper;
>     import com.powernode.mybatis.pojo.Clazz;
>     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);
>         }
>         @Test
>         public void selectByAssociation()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
>             Student student = mapper.selectByAssociation(2);
>             logger.info(student.toString());
>             SqlSessionUtils.close(sqlSession);
>         }
>         @Test
>         public void selectByIdStepTwo()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
>             Student student = mapper.selectByIDStepOne(1);
>             logger.info(student.getSname().toString());
>             //程序执行到这里了,我想看看班级名字
>             logger.info(student.getClazz().getCname());
>             SqlSessionUtils.close(sqlSession);
>         }
>         @Test
>         public void clazzResultMap()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             ClazzMapper mapper = sqlSession.getMapper(ClazzMapper.class);
>             Clazz clazz = mapper.selectByCollection(1000);
>             logger.info(clazz.toString());
>         }
>     }
> 
>     package com.powernode.mybatis.Test;
>     
>     import com.powernode.mybatis.mappers.ClazzMapper;
>     import com.powernode.mybatis.mappers.StudentMapper;
>     import com.powernode.mybatis.pojo.Clazz;
>     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);
>         }
>         @Test
>         public void selectByAssociation()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
>             Student student = mapper.selectByAssociation(2);
>             logger.info(student.toString());
>             SqlSessionUtils.close(sqlSession);
>         }
>         @Test
>         public void selectByIdStepTwo()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
>             Student student = mapper.selectByIDStepOne(1);
>             logger.info(student.getSname().toString());
>             //程序执行到这里了,我想看看班级名字
>             logger.info(student.getClazz().getCname());
>             SqlSessionUtils.close(sqlSession);
>         }
>         @Test
>         public void clazzResultMap()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             ClazzMapper mapper = sqlSession.getMapper(ClazzMapper.class);
>             Clazz clazz = mapper.selectByCollection(1000);
>             logger.info(clazz.toString());
>         }
>     }