學(xué)生和班級的例子：
一個(gè)學(xué)生在某一時(shí)期只能在一個(gè)班級：張三在java開發(fā)班勃刨，一對一
一個(gè)班級肯定至少有一個(gè)或多個(gè)學(xué)生：java開發(fā)班有6個(gè)學(xué)生波材，一對多
那么。對應(yīng)實(shí)際開發(fā)時(shí)如何處理呢身隐？
表：Clazz和Student表如何設(shè)計(jì)
主表應(yīng)該為Clazz廷区，從表應(yīng)該為Student

image.png

image.png

實(shí)體類

package com.huhong.model;

import java.io.Serializable;
import java.util.List;

public class Clazz implements Serializable {
    private Integer id;

    private String name;

    private List<Student> students;//duo

    private static final long serialVersionUID = 1L;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }
}

package com.huhong.model;

import java.io.Serializable;

public class Student implements Serializable {
    private Integer id;

    private String name;

    private String sex;

    private Clazz clazz;//1

    private static final long serialVersionUID = 1L;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public Clazz getClazz() {
        return clazz;
    }

    public void setClazz(Clazz clazz) {
        this.clazz = clazz;
    }
}

mapper映射文件

<?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.huhong.dao.ClazzDao" >
  <resultMap id="ClazzMap" type="com.huhong.model.Clazz" >
    <id column="id" property="id" jdbcType="INTEGER" />
    <result column="name" property="name" jdbcType="VARCHAR" />
    <collection property="students" column="id" javaType="ArrayList"
                ofType="com.huhong.model.Student"
                select="com.huhong.dao.StudentDao.selectStudentByClazzId"
                fetchType="lazy">
      <id column="id" property="id"/>
      <result column="name" property="name"/>
      <result column="sex" property="sex"/>
    </collection>
  </resultMap>
  <sql id="Base_Column_List" >
    id, name
  </sql>
  <select id="selectByPrimaryKey" resultMap="ClazzMap" parameterType="java.lang.Integer" >
    select 
    <include refid="Base_Column_List" />
    from tb_clazz
    where id = #{id,jdbcType=INTEGER}
  </select>
  <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" >
    delete from tb_clazz
    where id = #{id,jdbcType=INTEGER}
  </delete>
  <insert id="insert" parameterType="com.huhong.model.Clazz" >
    insert into tb_clazz (id, name)
    values (#{id,jdbcType=INTEGER}, #{name,jdbcType=VARCHAR})
  </insert>
  <insert id="insertSelective" parameterType="com.huhong.model.Clazz" >
    insert into tb_clazz
    <trim prefix="(" suffix=")" suffixOverrides="," >
      <if test="id != null" >
        id,
      </if>
      <if test="name != null" >
        name,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides="," >
      <if test="id != null" >
        #{id,jdbcType=INTEGER},
      </if>
      <if test="name != null" >
        #{name,jdbcType=VARCHAR},
      </if>
    </trim>
  </insert>
  <update id="updateByPrimaryKeySelective" parameterType="com.huhong.model.Clazz" >
    update tb_clazz
    <set >
      <if test="name != null" >
        name = #{name,jdbcType=VARCHAR},
      </if>
    </set>
    where id = #{id,jdbcType=INTEGER}
  </update>
  <update id="updateByPrimaryKey" parameterType="com.huhong.model.Clazz" >
    update tb_clazz
    set name = #{name,jdbcType=VARCHAR}
    where id = #{id,jdbcType=INTEGER}
  </update>
</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.huhong.dao.StudentDao" >
  <resultMap id="BaseResultMap" type="com.huhong.model.Student" >
    <id column="id" property="id" jdbcType="INTEGER" />
    <result column="name" property="name" jdbcType="VARCHAR" />
    <result column="sex" property="sex" jdbcType="VARCHAR" />
    <association property="clazz" javaType="com.huhong.model.Clazz">
       <id property="id" column="cid"/>
      <result property="name" column="cname"/>
    </association>
  </resultMap>
  <sql id="Base_Column_List" >
    id, name, sex, clazz_id
  </sql>
  <select id="selectStudentByClazzId" parameterType="int" resultMap="BaseResultMap">
    select *  from tb_student where clazz_id = #{id}
  </select>
  <select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Integer" >
     select s.*,c.id cid,c.name cname FROM tb_student s,tb_clazz c where c.id = s.clazz_id and s.id = #{id}
  </select>
  <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" >
    delete from tb_student
    where id = #{id,jdbcType=INTEGER}
  </delete>
  <insert id="insert" parameterType="com.huhong.model.Student" >
    insert into tb_student (id, name, sex, 
      clazz_id)
    values (#{id,jdbcType=INTEGER}, #{name,jdbcType=VARCHAR}, #{sex,jdbcType=VARCHAR}, 
      #{clazz_id,jdbcType=INTEGER})
  </insert>
  <insert id="insertSelective" parameterType="com.huhong.model.Student" >
    insert into tb_student
    <trim prefix="(" suffix=")" suffixOverrides="," >
      <if test="id != null" >
        id,
      </if>
      <if test="name != null" >
        name,
      </if>
      <if test="sex != null" >
        sex,
      </if>
      <if test="clazz_id != null" >
        clazz_id,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides="," >
      <if test="id != null" >
        #{id,jdbcType=INTEGER},
      </if>
      <if test="name != null" >
        #{name,jdbcType=VARCHAR},
      </if>
      <if test="sex != null" >
        #{sex,jdbcType=VARCHAR},
      </if>
      <if test="clazz_id != null" >
        #{clazz_id,jdbcType=INTEGER},
      </if>
    </trim>
  </insert>
  <update id="updateByPrimaryKeySelective" parameterType="com.huhong.model.Student" >
    update tb_student
    <set >
      <if test="name != null" >
        name = #{name,jdbcType=VARCHAR},
      </if>
      <if test="sex != null" >
        sex = #{sex,jdbcType=VARCHAR},
      </if>
      <if test="clazz_id != null" >
        clazz_id = #{clazz_id,jdbcType=INTEGER},
      </if>
    </set>
    where id = #{id,jdbcType=INTEGER}
  </update>
  <update id="updateByPrimaryKey" parameterType="com.huhong.model.Student" >
    update tb_student
    set name = #{name,jdbcType=VARCHAR},
      sex = #{sex,jdbcType=VARCHAR},
      clazz_id = #{clazz_id,jdbcType=INTEGER}
    where id = #{id,jdbcType=INTEGER}
  </update>
</mapper>

clazz.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ page isELIgnored ="false" %>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<html>
<body>
<h2>Clazz Info</h2>


編號： ${clazz.id}<br>
班級名稱： ${clazz.name}<br>
<c:forEach items="${students}" var="stu">
    ${stu.id}<br>
    ${stu.name}<br>
    ${stu.sex}<br>
</c:forEach>
</body>
</html>

student.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ page isELIgnored ="false" %>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<html>
<body>
<h2>Student Info</h2>

編號： ${student.id}<br>
學(xué)生姓名： ${student.name}<br>
學(xué)生性別：${student.sex}<br>
班級編號：${student.clazz.id}<br>
班級名稱：${student.clazz.name}

</body>
</html>

控制層

package com.huhong.controller;

import com.huhong.model.Clazz;
import com.huhong.model.Student;
import com.huhong.service.ClazzService;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;

import javax.annotation.Resource;
import java.util.ArrayList;
import java.util.List;

/**
 * Created by Tired on 2018/4/11.
 */
@Controller
public class ClazzController {
    @Resource
    private ClazzService clazzService;
    @RequestMapping("/showClazzInfo")
    public ModelAndView getClazzInfo()
    {
        ModelAndView mv = new ModelAndView("clazz");
       // this.addClazz();
       Clazz clazz =  clazzService.selectByPrimaryKey(2);
       Clazz clazz1 = clazzService.selectByPrimaryKey(2);
       //List<Student> students = clazz.getStudents();
       mv.addObject("clazz",clazz);
       //mv.addObject("students",students);

       return mv;
    }
    public   void addClazz()
    {
        Clazz clazz = new Clazz();
        clazz.setId(2);
        clazz.setName("機(jī)電1班");
        clazzService.insertSelective(clazz);
        System.out.println(clazz.getName());
    }
}

package com.huhong.controller;

import com.huhong.model.Student;
import com.huhong.service.StudentService;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;

import javax.annotation.Resource;

/**
 * Created by Tired on 2018/4/12.
 */
@Controller
public class StudentController {
    @Resource
    private StudentService studentService;
    @RequestMapping("/showStudentInfo")
    public ModelAndView getStudentInfo()
    {
        ModelAndView mv = new ModelAndView("student");
        Student student = studentService.selectByPrimaryKey(2);
        mv.addObject("student",student);
        return mv;
    }
}