mybatis文件映射之鉴别器discriminator标签
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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 ="last_name"="lastName"="gender"="gender"="email"="email"discriminator javaType="string" column> case value="0" resultType="com.gong.mybatis.bean.Employee"> association property="dept" select="com.gong.mybatis.dao.DepartmentMapper.getDeptById" column="d_id"</associationcase="1"/> /> discriminator> resultMapselect id="getEmpByIdStep" resultMap> 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 ="getDeptById"="com.gong.mybatis.bean.Department" select * from tbl_department where id=#{id} > 进行测试： package com.gong.mybatis.test; import java.io.IOException; java.io.InputStream; java.util.List; java.util.Map; org.apache.ibatis.io.Resources; org.apache.ibatis.session.SqlSession; org.apache.ibatis.session.SqlSessionFactory; org.apache.ibatis.session.SqlSessionFactoryBuilder; org.junit.Test; com.gong.mybatis.bean.Department; com.gong.mybatis.bean.Employee; com.gong.mybatis.dao.DepartmentMapper; 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 void test() IOException { SqlSessionFactory sqlSessionFactory = getSqlSessionFactory(); SqlSession openSession = sqlSessionFactory.openSession(); try { EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.); 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) 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) 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) 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) email未被修改，且可以查到部门的信息。 （编辑：李大同） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |