Mybatis从入门到精通——鉴别器使用（16）

约定不等于承诺〃 2023-07-12 14:53 22阅读 0赞

# 一、鉴别器 #

Mybatis的鉴别器（discriminator）是ResultMap的子标签，它提供了可以根据不同结果信息执行不同查询操作，只能用于分步查询中。

# 二、使用说明 #

1.查询结果集：

</discriminator>

</resultMap>

2.分步查询结果集（必须继承查询结果集，且type要和查询结果集一致）：

结果集1：

</collection>

</resultMap>

结果集2：

</collection>

</resultMap>

注意：

1.鉴别器除了需要使用discriminator标签进行判断之外，其它的都和分步查询类似。

2.分步查询结果集必须继承查询结果集，且type属性值要和查询结果集一致。

# 三、表关系说明 #

user表结构和数据：

DROP TABLE IF EXISTS `user`;
    CREATE TABLE `user` (
      `id` int(20) NOT NULL AUTO_INCREMENT,
      `user_name` varchar(60) DEFAULT NULL COMMENT '用户名称',
      `real_name` varchar(60) DEFAULT NULL COMMENT '真实名称',
      `sex` char(1) NOT NULL DEFAULT '1' COMMENT '性别',
      `mobile` varchar(20) DEFAULT NULL COMMENT '电话',
      `email` varchar(60) DEFAULT NULL COMMENT '邮箱',
      `note` varchar(200) DEFAULT NULL COMMENT '备注',
      `position_id` int(20) DEFAULT NULL,
      PRIMARY KEY (`id`),
      KEY `fk_4` (`position_id`)
    ) ENGINE=InnoDB AUTO_INCREMENT=127 DEFAULT CHARSET=utf8;
    
    INSERT INTO `user` VALUES ('1', 'lison', '李小宇', '1', '18232344223', 'lison@qq.com', 'lison的备注', '1');
    INSERT INTO `user` VALUES ('2', 'james', '陈大雷', '1', '18454656125', 'james@qq.com', 'james的备注', '2');
    INSERT INTO `user` VALUES ('3', 'cindy', '王美丽', '0', '14556656512', 'xxoo@163.com', 'cindy\'s note', '1');
    INSERT INTO `user` VALUES ('126', 'mark', '毛毛', '0', '18635457815', 'xxoo@163.com', 'mark\'s note', '1');

health\_repormale表结构和数据（男性体检报告表）：

DROP TABLE IF EXISTS `health_repormale`;
    CREATE TABLE `health_repormale` (
      `id` int(20) NOT NULL AUTO_INCREMENT,
      `check_project` varchar(50) DEFAULT NULL,
      `detail` varchar(100) DEFAULT NULL,
      `user_id` int(20) DEFAULT NULL,
      PRIMARY KEY (`id`)
    ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
    
    INSERT INTO `health_repormale` VALUES ('1', '男人项目1', '达标', '1');
    INSERT INTO `health_repormale` VALUES ('2', '男人项目2', '达标', '1');
    INSERT INTO `health_repormale` VALUES ('3', '男人项目3', '达标', '1');

health\_reporfemale表结构和数据（女性体检报告表）：

DROP TABLE IF EXISTS `health_reporfemale`;
    CREATE TABLE `health_reporfemale` (
      `id` int(20) NOT NULL AUTO_INCREMENT,
      `item` varchar(50) DEFAULT NULL,
      `score` decimal(10,2) DEFAULT NULL,
      `user_id` int(20) DEFAULT NULL,
      PRIMARY KEY (`id`)
    ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
    
    INSERT INTO `health_reporfemale` VALUES ('1', '女生项目1', '80.00', '3');
    INSERT INTO `health_reporfemale` VALUES ('2', '女生项目2', '60.00', '3');
    INSERT INTO `health_reporfemale` VALUES ('3', '女生项目3', '90.00', '3');

# 三、案例 #

案例说明：体检报告分为男性和女性，当用户的sex为1时查询男性体检报告表并返回结果，为用户的sex为0时查询女性的体检报告表并返回结果。

mapper映射文件：

UserMapper.xml：

<?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.my.mapper.UserMapper">
    
      <resultMap id="BaseResultMap" type="com.my.entity.User">
        <id column="id" jdbcType="INTEGER" property="id" />
        <result column="user_name" jdbcType="VARCHAR" property="userName" />
        <result column="real_name" jdbcType="VARCHAR" property="realName" />
        <result column="sex" jdbcType="CHAR" property="sex" />
        <result column="mobile" jdbcType="VARCHAR" property="mobile" />
        <result column="email" jdbcType="VARCHAR" property="email" />
        <result column="note" jdbcType="VARCHAR" property="note" />
        <result column="position_id" jdbcType="INTEGER" property="positionId" />
      </resultMap>
    
      <sql id="Base_Column_List">
        id, user_name, real_name, sex, mobile, email, note, position_id
      </sql>
    
      <resultMap id="UserAndHealthReportsResultMap" type="com.my.entity.User" extends="BaseResultMap">
        
        <discriminator javaType="String" column="sex">
          <case value="1" resultMap="HealthReportMaleResultMap"></case>
          <case value="0" resultMap="HealthReportFemale"></case>
        </discriminator>
      </resultMap>
    
      
      <resultMap id="HealthReportMaleResultMap" type="com.my.entity.User" extends="UserAndHealthReportsResultMap">
        <collection property="healthReports" column="id" select="com.my.mapper.HealthReportMaleMapper.selectByUserId"></collection>
      </resultMap>
    
      
      <resultMap id="HealthReportFemale" type="com.my.entity.User" extends="UserAndHealthReportsResultMap">
        <collection property="healthReports" column="id" select="com.my.mapper.HealthReportFemaleMapper.selectByUserId"></collection>
      </resultMap>
    
      <select id="selectUserAndHealthReportsById" parameterType="Integer" resultMap="UserAndHealthReportsResultMap">
        select
        <include refid="Base_Column_List" />
        from user
        where id = #{id,jdbcType=INTEGER}
      </select>
    
    </mapper>

HealthReportMaleMapper.xml：

HealthReportFemaleMapper.xml：

User类属性：

public class User {
        private Integer id;
    
        private String userName;
    
        private String realName;
    
        private String sex;
    
        private String mobile;
    
        private String email;
    
        private String note;
    
        private Integer positionId;
    
        private List<HealthReport>  healthReports;
    
    
    }

HealthReport类：

public abstract class HealthReport {
    	
    	private int id;
    
    	public int getId() {
    		return id;
    	}
    
    	public void setId(int id) {
    		this.id = id;
    	}
    	
    	public abstract String getDescription();
    	
    }

HealthReportFemale类：

public class HealthReportFemale extends HealthReport{
    
        private String item;
    
        private Double score;
    
        private Integer userId;
    
    
        @Override
        public String getDescription() {
            String rank = score >= 60 ? "达标" : "不达标";
            return "检查项目："+item+",成绩："+rank;
        }
    
    }

HealthReportMale类：

public class HealthReportMale extends HealthReport{
    
        private String checkProject;
    
        private String detail;
    
        private Integer userId;
    
        @Override
        public String getDescription() {
            return "检查项目："+checkProject+",成绩："+detail;
        }
    
    }

说明：为了阅读方便，以上几个实体类省略了一些get/set和toString方法。

测试代码：

public class MybatisTest {
    
        private SqlSessionFactory sqlSessionFactory;
    
        @Before
        public void init() throws IOException {
            String resource = "mybatis-config.xml";
            //1.使用mybatis的工具读取配置文件
            InputStream inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
            //2.创建sqlSessionFactory
            sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);
            inputStream.close();
        }
    
        /**
         * 测试鉴别器
         */
        @Test
        public void testDiscriminator() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            User user = userMapper.selectUserAndHealthReportsById(1);
            System.out.println(user);
            User user1 = userMapper.selectUserAndHealthReportsById(3);
            System.out.println(user1);
        }
        
    }