mybatis文件映射之鉴别器discriminator标签

2020-01-20 21:00:09 阅读：399 来源： 互联网

标签：01 20 java 鉴别器 DEBUG employee mybatis discriminator id

mybatis可以使用鉴别器判断某列的值，然后根据某列的值改变封装行为。

比如说：

如果是女生（gender=0）我们将部门信息提取出来，否则不提取；

如果是男生（gender=1），把last_name的值赋值给email；

EmployeeMapper.xml

    <resultMap type="com.gong.mybatis.bean.Employee" id="MyEmpDis">
        <id column="id" property="id"/>
        <result column="last_name" property="lastName"/>
        <result column="gender" property="gender"/>
        <result column="email" property="email"/>
        <discriminator javaType="string" column="gender">
            <case value="0" resultType="com.gong.mybatis.bean.Employee">
                <association property="dept" select="com.gong.mybatis.dao.DepartmentMapper.getDeptById"
                column="d_id">
                </association>
            </case>
            <case value="1" resultType="com.gong.mybatis.bean.Employee">
                <id column="id" property="id"/>
                <result column="last_name" property="lastName"/>
                <result column="gender" property="gender"/>
                <result column="last_name" property="email"/>
            </case>
        </discriminator>
    </resultMap>
    <select id="getEmpByIdStep" resultMap="MyEmpDis">
        select * from tbl_employee where id=#{id}
    </select>

说明：distriminator中的javaType指定数据库中字段对应着java中的属性的类型，column属性为列名称。case标签中value属性标识数据库中列的值，resultType指定封装的结果类型，不可少。

DepartmentMapper.xml

    <select id="getDeptById" resultType="com.gong.mybatis.bean.Department">
        select * from tbl_department where id=#{id}
    </select>

进行测试：

package com.gong.mybatis.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.Map;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.gong.mybatis.bean.Department;
import com.gong.mybatis.bean.Employee;
import com.gong.mybatis.dao.DepartmentMapper;
import com.gong.mybatis.dao.EmployeeMapperPlus;

public class TestMybatis2 {
    
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream is = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(is);
    }

    @Test
    public void test() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession();
        try {
            EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);
            Employee employee = mapper.getEmpByIdStep(3);
            System.out.println(employee.getLastName());
            System.out.println(employee.getDept());
            openSession.commit();
        } finally {
            openSession.close();
        }
        
    }

}

首先测试的是gender=0的情况：

DEBUG 01-20 20:47:37,503 ==> Preparing: select * from tbl_employee where id=? (BaseJdbcLogger.java:145)
DEBUG 01-20 20:47:37,590 ==> Parameters: 3(Integer) (BaseJdbcLogger.java:145)
DEBUG 01-20 20:47:37,757 <== Total: 1 (BaseJdbcLogger.java:145)
小红
DEBUG 01-20 20:47:37,759 ==> Preparing: select * from tbl_department where id=? (BaseJdbcLogger.java:145)
DEBUG 01-20 20:47:37,760 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145)
DEBUG 01-20 20:47:37,763 <== Total: 1 (BaseJdbcLogger.java:145)
Department [id=1, deptName=开发部]

可以查到部门的信息。

接下来是gender=1的情况：

Employee employee = mapper.getEmpByIdStep(1);

DEBUG 01-20 20:53:32,581 ==> Preparing: select * from tbl_employee where id=? (BaseJdbcLogger.java:145)
DEBUG 01-20 20:53:32,647 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145)
DEBUG 01-20 20:53:32,708 <== Total: 1 (BaseJdbcLogger.java:145)
xiximayou
null

发现部门信息是查不到的。

再进行gender=1时的情况：

            Employee employee = mapper.getEmpByIdStep(1);
            System.out.println(employee);
            System.out.println(employee.getDept());

DEBUG 01-20 20:54:39,440 ==> Preparing: select * from tbl_employee where id=? (BaseJdbcLogger.java:145)
DEBUG 01-20 20:54:39,480 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145)
DEBUG 01-20 20:54:39,555 <== Total: 1 (BaseJdbcLogger.java:145)
Employee [id=1, lastName=xiximayou, gender=1, email=xiximayou, dept=null]
null

email被修改，且部门信息查不到。

gender=0的情况：

        Employee employee = mapper.getEmpByIdStep(3);
        System.out.println(employee);
        System.out.println(employee.getDept());

DEBUG 01-20 20:56:19,177 ==> Preparing: select * from tbl_employee where id=? (BaseJdbcLogger.java:145)
DEBUG 01-20 20:56:19,221 ==> Parameters: 3(Integer) (BaseJdbcLogger.java:145)
DEBUG 01-20 20:56:19,384 <== Total: 1 (BaseJdbcLogger.java:145)
DEBUG 01-20 20:56:19,385 ==> Preparing: select * from tbl_department where id=? (BaseJdbcLogger.java:145)
DEBUG 01-20 20:56:19,386 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145)
DEBUG 01-20 20:56:19,389 <== Total: 1 (BaseJdbcLogger.java:145)
Employee [id=3, lastName=小红, gender=0, email=xiaohong@qq.com, dept=Department [id=1, deptName=开发部]]
Department [id=1, deptName=开发部]

email未被修改，且可以查到部门的信息。

标签：01,20,java,鉴别器,DEBUG,employee,mybatis,discriminator,id
来源： https://www.cnblogs.com/xiximayou/p/12219414.html

本站声明： 1. iCode9 技术分享网（下文简称本站）提供的所有内容，仅供技术学习、探讨和分享；
2. 关于本站的所有留言、评论、转载及引用，纯属内容发起人的个人观点，与本站观点和立场无关；
3. 关于本站的所有言论和文字，纯属内容发起人的个人观点，与本站观点和立场无关；
4. 本站文章均是网友提供，不完全保证技术分享内容的完整性、准确性、时效性、风险性和版权归属；如您发现该文章侵犯了您的权益，可联系我们第一时间进行删除；
5. 本站为非盈利性的个人网站，所有内容不会用来进行牟利，也不会利用任何形式的广告来间接获益，纯粹是为了广大技术爱好者提供技术内容和技术思想的分享性交流网站。

ICode9

mybatis文件映射之鉴别器discriminator标签