MyBatis 鉴别器（discriminator）的应用

我不是女神ヾ 2023-02-16 10:57 96阅读 0赞

> MyBatis 多表操作（一对多）：[https://yuanyu.blog.csdn.net/article/details/89603924][https_yuanyu.blog.csdn.net_article_details_89603924]

> 分步查询，但是男生执行的操作和女生不同
> 
>  *  如果查出的是女生：就把部门信息查询出来，否则不查询
>  *  如果是男生，把username这一列的值赋值给email

> 删除数据库中所有数据，从新插入 数据

-- 插入
    INSERT INTO t_dept(`id`, `dept_name`)
    VALUES ('8848', '开发部'),
           ('6699', '测试部');
    INSERT INTO t_employee(`id`, `d_id`, `username`, `gender`, `email`)
    VALUES ('1', '8848', '张三', '男', 'zhangsan@bug.com'),
           ('2', '8848', '李四', '女', 'lisi@bug.com'),
           ('3', '8848', 'tom', '男', 'tom@bug.com');
    -- 查询
    SELECT * FROM t_employee;
    SELECT * FROM t_dept;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz_size_16_color_FFFFFF_t_70][]

<resultMap type="cn.yuanyu.mybatis.entity.Employee" id="discriminatorResultMap">
        <id column="id" property="id"/>
        <result column="username" property="username"/>
        <result column="email" property="email"/>
        <result column="gender" property="gender"/>
        
        <discriminator javaType="string" column="gender">
            
            <case value="女" resultType="cn.yuanyu.mybatis.entity.Employee">
                <association property="dept"
                             select="cn.yuanyu.mybatis.mapper.DepartmentMapper.getDeptById"
                             column="d_id">
                </association>
            </case>
            
            <case value="男" resultType="cn.yuanyu.mybatis.entity.Employee">
                <id column="id" property="id"/>
                <result column="username" property="username"/>
                <result column="username" property="email"/>
                <result column="gender" property="gender"/>
            </case>
        </discriminator>
    </resultMap>
    <select id="discriminator" resultMap="discriminatorResultMap">
        select *
        from t_employee
        where id = #{id}
    </select>

<select id="getDeptById" resultType="cn.yuanyu.mybatis.entity.Department">
        select id, dept_name deptName
        from t_dept
        where id = #{id}
    </select>

public interface EmployeeMapper {
        /**
         * 根据id查询员工信息，如果是女生部门信息也返回，男生只返回用户信息
         *
         * @param id 用户id
         * @return Employee + Department
         */
        Employee discriminator(Integer id);
    }

@Test
    public void discriminator() {
        Employee zhangsan = employeeMapper.discriminator(1); //男
        System.out.println(zhangsan);
        Employee lisi = employeeMapper.discriminator(2); //女
        System.out.println(lisi);

男生输出示例：

==>  Preparing: select * from t_employee where id = ? 
    ==> Parameters: 1(Integer)
    <==    Columns: id, d_id, username, gender, email
    <==        Row: 1, 8848, 张三, 男, zhangsan@bug.com
    <==      Total: 1
    Employee(id=1, username=张三, email=张三, gender=男, dept=null)

女生输出示例：

==>  Preparing: select * from t_employee where id = ? 
    ==> Parameters: 2(Integer)
    <==    Columns: id, d_id, username, gender, email
    <==        Row: 2, 8848, 李四, 女, lisi@bug.com
    ====>  Preparing: select id, dept_name deptName from t_dept where id = ? 
    ====> Parameters: 8848(String)
    <====    Columns: id, deptName
    <====        Row: 8848, 开发部
    <====      Total: 1
    <==      Total: 1
    Employee(id=2, username=李四, email=lisi@bug.com, gender=女, dept=Department(id=8848, deptName=开发部, emps=null))

[https_yuanyu.blog.csdn.net_article_details_89603924]: https://yuanyu.blog.csdn.net/article/details/89603924
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200609164031674.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz,size_16,color_FFFFFF,t_70