Mybatis学习第23节 -- 鉴别器 discriminator

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discriminator或者叫做分类器

Vehicle类

 
package io.github.coinsjack.pojo;

import java.util.Date;

public class Vehicle {

    protected Integer id;
    protected String vin;
    protected Date year;
    protected String make;
    protected  String model;
    protected String color;

    public Vehicle() {
    }

    public Integer getId() {
        return id;
    }

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

Car继承自Vehicle

package io.github.coinsjack.pojo;

public class Car extends Vehicle {

    private Integer doorCount;

    public Car() {
    }

    public Integer getDoorCount() {
        return doorCount;
    }

    public void setDoorCount(Integer doorCount) {
        this.doorCount = doorCount;
    }

    @Override
    public String toString() {
        return "Car{" +
                "doorCount=" + doorCount +
                ", id=" + id +
                ", vin=‘" + vin + ‘‘‘ +
                ", year=" + year +
                ", make=‘" + make + ‘‘‘ +
                ", model=‘" + model + ‘‘‘ +
                ", color=‘" + color + ‘‘‘ +
                ‘}‘;
    }
}

Suv继承自Vehicle

package io.github.coinsjack.pojo;

public class Suv extends Vehicle{

    private Boolean allWheelDriveFlag;

    public Suv() {
    }
    public Boolean getAllWheelDriveFlag() {
        return allWheelDriveFlag;
    }
    public void setAllWheelDriveFlag(Boolean allWheelDriveFlag) {
        this.allWheelDriveFlag = allWheelDriveFlag;
    }
    @Override
    public String toString() {
        return "Suv{" +
                "allWheelDriveFlag=" + allWheelDriveFlag +
                ", id=" + id +
                ", vin=‘" + vin + ‘‘‘ +
                ", year=" + year +
                ", make=‘" + make + ‘‘‘ +
                ", model=‘" + model + ‘‘‘ +
                ", color=‘" + color + ‘‘‘ +
                ‘}‘;
    }
}
数据库表字段
id int(11) NO PRI auto_increment
vin varchar(50) YES   
year year(4) YES   
make varchar(50) YES   
model varchar(20) YES   
color varchar(20) YES   
vehicle_type int(11) YES   
door_count int(11) YES   
all_wheel_drive tinyint(1) YES   
通过vehicle_type判断是Car还是Suv, 就需要用到discriminator
 

VehicleMapper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="io.github.coinsjack.dao.VehicleMapper">

    <resultMap id="vehicleResultMap" type="Vehicle">
        <id column="id" property="id"/>
        <id column="vin" property="vin"/>
        <id column="year" property="year"/>
        <id column="make" property="make"/>
        <id column="model" property="model"/>
        <id column="color" property="color"/>
        <discriminator javaType="int" column="vehicle_type">
            <case value="1" resultType="Car">
                <result column="door_count" property="doorCount"/>
            </case>
            <case value="2" resultType="Suv">
                <result column="all_wheel_drive" property="allWheelDriveFlag"/>
            </case>
        </discriminator>
    </resultMap>

    <select id="getVehicleById" resultMap="vehicleResultMap">
        select * from tb_vehicle
        WHERE `id` = #{id};
    </select>
</mapper>

测试

@Test
public void testGetVehicleById() {
        SqlSession sqlSession = MyBatisUtil.getSqlSession();
        VehicleMapper vehicleMapper= sqlSession.getMapper(VehicleMapper.class);

        System.out.printf("查询结果: %s%n", vehicleMapper.getVehicleById(5));;
        System.out.printf("查询结果: %s%n", vehicleMapper.getVehicleById(6));;
}

测试结果

2018-12-29 17:38:29,567 [main] DEBUG [io.github.coinsjack.dao.VehicleMapper.getVehicleById] - ==> Preparing: select * from tb_vehicle WHERE `id` = ?; 
2018-12-29 17:38:29,677 [main] DEBUG [io.github.coinsjack.dao.VehicleMapper.getVehicleById] - ==> Parameters: 5(Integer)
2018-12-29 17:38:29,750 [main] DEBUG [io.github.coinsjack.dao.VehicleMapper.getVehicleById] - <== Total: 1
查询结果: Car{doorCount=4, id=5, vin=‘2627159999‘, year=Mon Jan 01 08:00:00 CST 2018, make=‘IDEA‘, model=‘DA-20‘, color=‘Black‘}
2018-12-29 17:38:29,762 [main] DEBUG [io.github.coinsjack.dao.VehicleMapper.getVehicleById] - ==> Preparing: select * from tb_vehicle WHERE `id` = ?; 
2018-12-29 17:38:29,763 [main] DEBUG [io.github.coinsjack.dao.VehicleMapper.getVehicleById] - ==> Parameters: 6(Integer)
2018-12-29 17:38:29,804 [main] DEBUG [io.github.coinsjack.dao.VehicleMapper.getVehicleById] - <== Total: 1
查询结果: Suv{allWheelDriveFlag=false, id=6, vin=‘2627159998‘, year=Mon Jan 01 08:00:00 CST 2018, make=‘IDEA‘, model=‘AA-19‘, color=‘Pink‘}

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