根据id查询员工的信息（tbl_employee表），如果查询出来的员工是女生（gender=0），则进而把该员工的部门信息查询出来；如果查询到的是男生（gender=1），就把last_name这一列的值封装到email这一JavaBean变量
1.使用resulyMap封装结果集
2.在resultMap标签内使用标签来进行性别的判断
1）判断结果为0时，使用标签来调用部门的映射文件中的查询方法
2）判断结果为1时，重新定义封装规则
EmployeeMapper.class
package dao; import bean.Employee; public interface EmployeeMapper { // 使用鉴别器查询 public Employee getEmpByDis(Integer id); }EmployeeMapper.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="dao.EmployeeMapper"> <resultMap type="bean.Employee" id="MyEmpsDis"> <id column="id" property="id" /> <result column="last_name" property="lastName" /> <result column="email" property="email" /> <result column="gender" property="gender" /> <!-- column:指定要判别的列名 javaType:要判别的列的值对应的java类型（数据类型or对象类型） --> <discriminator javaType="string" column="gender"> <!-- value为要判别的列的不同取值 ，0为女生，1为男生 resultType:指定封装的结果类型 ，不能缺省，也可以使用resultMap --> <!-- 女生：查部门 --> <case value="0" resultType="bean.Employee"> <association property="dept" select="dao.DepartmentMapper.getDeptById" column="d_id"></association> </case> <!-- 男生：重新定义封装方法 --> <case value="1" resultType="bean.Employee"> <id column="id" property="id" /> <result column="last_name" property="lastName" /> <result column="last_name" property="email" /> <!-- 把last_name赋值给email --> <result column="gender" property="gender" /> </case> </discriminator> </resultMap> <!-- 对应的接口中的方法：public Employee getEmpByDis(Integer id); --> <select id="getEmpByDis" resultMap="MyEmpsDis"> select * from tbl_employee where id = #{id} </select> </mapper>DepartmentMapper.java
package dao; import bean.Department; public interface DepartmentMapper { public Department getDeptById(Integer id); }DepartmentMapper.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="dao.DepartmentMapper"> <!-- 对应的接口方法：public Department getDeptById(Integer id); --> <select id="getDeptById" resultType="bean.Department"> select id,dept_name departmentName from tbl_dept where id = #{id} </select> </mapper>测试方法：
package test; import java.io.IOException; import java.io.InputStream; 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 bean.Employee; import dao.EmployeeMapper; public class MyBatisTest { // 获取SqlSessionfactory对象的方法 public SqlSessionFactory getSqlSessionFactory() throws IOException { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); return new SqlSessionFactoryBuilder().build(inputStream); } @Test public void test() throws IOException { SqlSessionFactory sqlSessionFactory = getSqlSessionFactory(); SqlSession openSession = sqlSessionFactory.openSession(); try { EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class); Employee empByDis = mapper.getEmpByDis(1); System.out.println(empByDis); System.out.println(empByDis.getDept()); Employee empByDis2 = mapper.getEmpByDis(4); System.out.println(empByDis2); System.out.println(empByDis2.getDept()); } finally { openSession.close(); } } }测试结果：
DEBUG 11-02 15:05:26,487 ==> Preparing: select * from tbl_employee where id = ? (BaseJdbcLogger.java:145) DEBUG 11-02 15:05:26,520 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145) DEBUG 11-02 15:05:26,541 <== Total: 1 (BaseJdbcLogger.java:145) Employee [id=1, lastName=Admin, email=Admin, gender=1] null DEBUG 11-02 15:05:26,545 ==> Preparing: select * from tbl_employee where id = ? (BaseJdbcLogger.java:145) DEBUG 11-02 15:05:26,548 ==> Parameters: 4(Integer) (BaseJdbcLogger.java:145) DEBUG 11-02 15:05:26,552 ====> Preparing: select id,dept_name departmentName from tbl_dept where id = ? (BaseJdbcLogger.java:145) DEBUG 11-02 15:05:26,553 ====> Parameters: 1(Integer) (BaseJdbcLogger.java:145) DEBUG 11-02 15:05:26,556 <==== Total: 1 (BaseJdbcLogger.java:145) DEBUG 11-02 15:05:26,557 <== Total: 1 (BaseJdbcLogger.java:145) Employee [id=4, lastName=tina, email=tina.com, gender=0] Department [id=1, departmentName=开发部]从查询结果可以开出，查询到男生时，并没有去查他的部门信息，因此输出部门时输出结果为null，反而他的email的值与lastName的值相同，因此时使用了重新定义的封装规则；查询到女生时，可以输出她所在的部门信息，且email与lastName值不相同，并且查询女生的部门信息这里使用到了分步查询，利用懒加载，使得只有再需要输出部门信息时才会去发送查询部门的sql请求
p.s.具体的JavaBean实体类的定义与数据库表的定义、以及全局配置文件可参考其他博客
