MyBatis的discriminator 鉴别器使用(十一)上-阿里云开发者社区

MyBatis的discriminator 鉴别器使用(十一)上

2021-12-27 292

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简介： MyBatis的discriminator 鉴别器使用(十一)

一. MyBatis的鉴别器

在resultMap 里面，除了 allocation 一对一，collection 一对多之外，还有一个discriminator 鉴别器，可以根据类中某个属性的值不同，去执行不同的resultMap 结果。如,User 类中有一个sex 性别的属性，需要体检，那么就会有一个男生的健康表，一个女生的健康表，对应user 表中的外键。在查询的时候，会根据sex中的性别不同，去不同的表中查询结果。如果女生去了解男生的健康表，那会出问题的，当然，如果男生去了解女生的健康表，也是会出现问题的，所以这个时候，就需要discriminator 鉴别器了。

数据库表信息:

User表:

男生健康表 boy_healthy:

女生健康表 girl_healthy:

POJO 对象类:

User.java

package com.yjl.pojo;
/**
 @author:yuejl
 @date: 2019年6月15日 上午11:11:02
 @Description Mybatis 使用的基本类 User
*/
public class User {
  /**
   * @param id id编号，自增
   * @param name 姓名
   * @param age 年龄
   * @param sex 性别
   * @param description 描述
   */
  private Integer id;
  private String name;
  private Integer age;
  private String sex;
  private String description;
  public User(){
  }
  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 Integer getAge() {
    return age;
  }
  public void setAge(Integer age) {
    this.age = age;
  }
  public String getSex() {
    return sex;
  }
  public void setSex(String sex) {
    this.sex = sex;
  }
  public String getDescription() {
    return description;
  }
  public void setDescription(String description) {
    this.description = description;
  }
  public String toString() {
    return "User [id=" + id + ", name=" + name + ", age=" + age + ", sex=" + sex + ", description=" + description
        + "]";
  }
}

男生健康 Boy_Healthy.java

package com.yjl.pojo;
/**
@atuhor:yuejl
@Description: 男性健康表
*/
public class BoyHealthy {
  /**
   * @param id 编号
   * @param height 高度
   * @param weight 体重
   * @param xin 心
   * @param gan 肝
   * @param qianleixian 前列腺
   * @param description 描述
   */
  private int id;
  private Double height;
  private Double weight;
  private String xin;
  private String gan;
  private String qianleixian;
  private String description;
  //对于员工的处理
  private User userId;
  public int getId() {
    return id;
  }
  public void setId(int id) {
    this.id = id;
  }
  public Double getHeight() {
    return height;
  }
  public void setHeight(Double height) {
    this.height = height;
  }
  public Double getWeight() {
    return weight;
  }
  public void setWeight(Double weight) {
    this.weight = weight;
  }
  public String getXin() {
    return xin;
  }
  public void setXin(String xin) {
    this.xin = xin;
  }
  public String getGan() {
    return gan;
  }
  public void setGan(String gan) {
    this.gan = gan;
  }
  public String getQianleixian() {
    return qianleixian;
  }
  public void setQianleixian(String qianleixian) {
    this.qianleixian = qianleixian;
  }
  public String getDescription() {
    return description;
  }
  public void setDescription(String description) {
    this.description = description;
  }
  public User getUserId() {
    return userId;
  }
  public void setUserId(User userId) {
    this.userId = userId;
  }
  @Override
  public String toString() {
    return "BoyHealthy [id=" + id +", height=" + height + ", weight=" + weight + ", xin="
        + xin + ", gan=" + gan + ", qianleixian=" + qianleixian + ", description=" + description + "]";
  }
}

女生健康表 Girl_Healthy.java

package com.yjl.pojo;
/**
@atuhor:yuejl
@Description: 女性健康表
*/
public class GirlHealthy {
  /**
   * @param id 编号
   * @param height 高度
   * @param weight 体重
   * @param xin 心
   * @param gan 肝
   * @param zigon 子宫
   * @param description 描述
   */
  private int id;
  private Double height;
  private Double weight;
  private String xin;
  private String gan;
  private String zigong;
  private String description;
  //引入员工的对象
  private User user;
  public int getId() {
    return id;
  }
  public void setId(int id) {
    this.id = id;
  }
  public Double getHeight() {
    return height;
  }
  public void setHeight(Double height) {
    this.height = height;
  }
  public Double getWeight() {
    return weight;
  }
  public void setWeight(Double weight) {
    this.weight = weight;
  }
  public String getXin() {
    return xin;
  }
  public void setXin(String xin) {
    this.xin = xin;
  }
  public String getGan() {
    return gan;
  }
  public void setGan(String gan) {
    this.gan = gan;
  }
  public String getZigong() {
    return zigong;
  }
  public void setZigong(String zigong) {
    this.zigong = zigong;
  }
  public String getDescription() {
    return description;
  }
  public void setDescription(String description) {
    this.description = description;
  }
  public User getUser() {
    return user;
  }
  public void setUser(User user) {
    this.user = user;
  }
  @Override
  public String toString() {
    return "GirlHealthy [id=" + id +", height=" + height + ", weight=" + weight + ", xin="
        + xin + ", gan=" + gan + ", zigong=" + zigong + ", description=" + description + "]";
  }
}

需要将员工与健康表进行关联，一对多的形式，为了不改变实体对象的结构，故最好是创建一个Bean, 用来接收。当然，也可以用一对多的形式，但是不建议那样写。

男生健康Bean. Boy_Bean.

package com.yjl.pojo;
import java.util.List;
/**
@atuhor:yuejl
@Description: 类描述
*/
public class BoyBean extends User{
  private List<BoyHealthy> healthyList;
  public List<BoyHealthy> getHealthyList() {
    return healthyList;
  }
  public void setHealthyList(List<BoyHealthy> healthyList) {
    this.healthyList = healthyList;
  }
}

女生健康Bean. Girl_Bean.

package com.yjl.pojo;
import java.util.List;
/**
@atuhor:yuejl
@Description: 类描述
*/
public class GirlBean extends User{
  /**
   * 一个员工，可能对应多个不同的体检表。 当然，也可以是单个的。 原理都一样。
   */
  private List<GirlHealthy> healthyList;
  public List<GirlHealthy> getHealthyList() {
    return healthyList;
  }
  public void setHealthyList(List<GirlHealthy> healthyList) {
    this.healthyList = healthyList;
  }
}

二. 根据员工编号嵌套select 查询结果

UserMapper.java 接口：

public User getUserById(int id);

UserMapper.xml sql语句：

    <resultMap type="user" id="userResultMapWithDiscriminator">
    <!-- 员工的基本属性。 -->
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="sex" column="sex"/>
    <result property="age" column="age"/>
    <result property="description" column="description"/>
    <!-- 鉴别器 ，写上类型-->
    <discriminator javaType="string" column="sex">
      <!--根据不同的值，执行不同的resultMap-->
      <case value="男" resultMap="boyHealthyMap"></case>
      <case value="女" resultMap="girlHealthyMap"></case>
    </discriminator>
  </resultMap>
  <select id="getUserById" parameterType="int" resultMap="userResultMapWithDiscriminator">
    select * from user where id=#{id}
  </select>
  <!-- 关于男性的鉴别器 -->
  <resultMap type="boyBean" id="boyHealthyMap" extends="userResultMapWithDiscriminator">
    <collection property="healthyList" ofType="boyHealthy" javaType="ArrayList"
    column="id" select="com.yjl.mapper.BoyHealthyMapper.findHealthyByUserId">
    </collection>
  </resultMap>
  <!-- 关于女性的鉴别器 -->
  <resultMap type="girlBean" id="girlHealthyMap" extends="userResultMapWithDiscriminator">
    <collection property="healthyList" ofType="girlHealthy" javaType="ArrayList"
    column="id" select="com.yjl.mapper.GirlHealthyMapper.findHealthyByUserId">
    </collection>
  </resultMap>

那么对应就有一个

BoyHealthyMapper.java 提供了一个接口:

public List<BoyHealthy> findHealthyByUserId(@Param(value="userId") int userId);

BoyHealthyMapper.xml 的sql语句:

<?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.yjl.mapper.BoyHealthyMapper">
  <resultMap type="boyHealthy" id="boyHealthyMap">
    <id property="id" column="id"/>
    <result property="height" column="height"/>
    <result property="weight" column="weight"/>
    <result property="xin" column="xin"/>
    <result property="gan" column="gan"/>
    <result property="qianleixian" column="qianleixian"/>
    <result property="description" column="description"/>
  </resultMap>
  <select id="findHealthyByUserId" parameterType="int" resultMap="boyHealthyMap">
    select * from boy_healthy t where t.userId=#{userId}
  </select>
</mapper>

GirlHealthyMapper.java 也提供了一个接口:

public List<GirlHealthy> findHealthyByUserId(@Param(value="userId") int userId);

GirlHealthyMapper.xml 的sql语句:

<mapper namespace="com.yjl.mapper.GirlHealthyMapper">
  <resultMap type="girlHealthy" id="girlHealthyMap">
    <id property="id" column="id"/>
    <result property="height" column="height"/>
    <result property="weight" column="weight"/>
    <result property="xin" column="xin"/>
    <result property="gan" column="gan"/>
    <result property="zigong" column="zigong"/>
    <result property="description" column="description"/>
  </resultMap>
  <select id="findHealthyByUserId" parameterType="int" resultMap="girlHealthyMap">
    select * from girl_healthy t where t.userId=#{userId}
  </select>
</mapper>

测试方法:

  @Test
  public void getByIdTest(){
    SqlSession sqlSession=SqlSessionFactoryUtils.getSession();
    UserMapper userMapper=sqlSession.getMapper(UserMapper.class);
    User user=userMapper.getUserById(1);
    System.out.println("员工信息:"+user);
    if("男".equals(user.getSex())){
      //需要进行向下转化。
      BoyBean boyBean=(BoyBean)user;
      List<BoyHealthy> boyHList=boyBean.getHealthyList();
      boyHList.forEach(n ->System.out.println(n));
    }else{
      GirlBean girlBean=(GirlBean)user;
      List<GirlHealthy> girlHList=girlBean.getHealthyList();
      girlHList.forEach(n ->System.out.println(n));
    }
  }