概述
我们在if标签的博文MyBatis-11MyBatis动态SQL之【if】
中介绍了if的在select、update、delete中的用法，可以实现基本的条件判断， 但是却无法实现 if…else ,if ….else….的逻辑。
想要实现 if…else ,if ….else….这样的逻辑 就需要用到choose when otherwise标签了。
choose元素中包含了when和otherwise两个标签 ，一个choose中至少有一个when，有0个或者1个otherwise
需求
前置条件： sys_user表中，除了id是主键外，我们认为user_name也是唯一的，用户名不可重复。
假设有个这样的需求， 实现如下如下逻辑
- 当参数id有值时优先使用id查询
- 当没有id时就去判断用户名是否有值，如果有值就根据用户名全配
- 如果用户名也没有值，就是sql查询为空
实现步骤
1.UserMapper接口中添加接口方法
/** * * * @Title: selectSysUserByIdOrByUserName * * @Description: 根据用户id或者用户名查询用户 * * @param sysUser * @return * * @return: SysUser */ SysUser selectSysUserByIdOrByUserName(SysUser sysUser);
2.UserMapper.xml中添加动态SQL
<select id="selectSysUserByIdOrByUserName" resultType="com.artisan.mybatis.xml.domain.SysUser"> SELECT a.id, a.user_name userName, a.user_password userPassword, a.user_email userEmail, a.user_info userInfo, a.head_img headImg, a.create_time createTime FROM sys_user a WHERE 1=1 <choose> <when test="id != null "> and id = #{id} </when> <when test="userName!= null "> and user_name = #{userName} </when> <otherwise> and 1 = 2 </otherwise> </choose> </select>
使用choose when otherwise的时候逻辑要严密，避免由于某些值出现问题导致SQL出错。
在上述查询中，如果没有otherwise这个条件限制，当id和username都为空时，所有的用户都会被查询出来，但是我们在对引得接口方法中使用了SysUser作为返回值，所以当实际查询到多个结果时就会报错， 添加otherwise后，由于where 后的条件不满足，因此这种这种情况下查不到结果。
3.单元测试
@Test public void selectSysUserByIdOrByUserNameTest() { logger.info("selectSysUserByIdOrByUserNameTest"); // 获取SqlSession SqlSession sqlSession = getSqlSession(); try { // 获取UserMapper接口 UserMapper userMapper = sqlSession.getMapper(UserMapper.class); logger.info("======. 模拟传入了正确的id 没有传username或者传入了错误的userName======"); // 1. 模拟传入了正确的id 没有传username或者传入了错误的userName SysUser sysUser = new SysUser(); sysUser.setId(1001L); sysUser.setUserName("noExistName"); // 调用selectSysUserByIdOrByUserName,查询单个用户 SysUser user = userMapper.selectSysUserByIdOrByUserName(sysUser); // 期望不为空 Assert.assertNotNull(user); // userName 期望值为artisan Assert.assertEquals("artisan", user.getUserName()); logger.info(user); logger.info("======2. 模拟不传id,但是传入了正确的 userName======"); // 2. 模拟不传id,但是传入了正确的 userName sysUser = new SysUser(); sysUser.setId(null); sysUser.setUserName("admin"); user = userMapper.selectSysUserByIdOrByUserName(sysUser); // 期望不为空 Assert.assertNotNull(user); // 根据id查询 sysuser,然后获取userName 期望值为artisan Assert.assertEquals("admin", user.getUserName()); logger.info(user); logger.info("======3.什么都不传======"); // 2. 模拟不传id,但是传入了正确的 userName sysUser = new SysUser(); sysUser.setId(null); sysUser.setUserName(null); user = userMapper.selectSysUserByIdOrByUserName(sysUser); // 期望为空 Assert.assertNull(user); logger.info(user); } catch (Exception e) { e.printStackTrace(); } finally { sqlSession.close(); logger.info("sqlSession close successfully "); } }
日志
2018-04-21 19:46:51,942 INFO [main] (BaseMapperTest.java:26) - sessionFactory bulit successfully 2018-04-21 19:46:51,947 INFO [main] (BaseMapperTest.java:29) - reader close successfully 2018-04-21 19:46:51,951 INFO [main] (UserMapperTest.java:541) - selectSysUserByIdOrByUserNameTest 2018-04-21 19:46:51,979 INFO [main] (UserMapperTest.java:548) - ======. 模拟传入了正确的id 没有传username或者传入了错误的userName====== 2018-04-21 19:46:52,569 DEBUG [main] (BaseJdbcLogger.java:145) - ==> Preparing: SELECT a.id, a.user_name userName, a.user_password userPassword, a.user_email userEmail, a.user_info userInfo, a.head_img headImg, a.create_time createTime FROM sys_user a WHERE 1=1 and id = ? 2018-04-21 19:46:52,647 DEBUG [main] (BaseJdbcLogger.java:145) - ==> Parameters: 1001(Long) 2018-04-21 19:46:52,685 TRACE [main] (BaseJdbcLogger.java:151) - <== Columns: id, userName, userPassword, userEmail, userInfo, headImg, createTime 2018-04-21 19:46:52,686 TRACE [main] (BaseJdbcLogger.java:151) - <== Row: 1001, artisan, 123456, test@artisan.com, <<BLOB>>, <<BLOB>>, 2018-04-13 21:12:47.0 2018-04-21 19:46:52,694 DEBUG [main] (BaseJdbcLogger.java:145) - <== Total: 1 2018-04-21 19:46:52,695 INFO [main] (UserMapperTest.java:559) - SysUser [id=1001, userName=artisan, userPassword=123456, userEmail=test@artisan.com, userInfo=测试用户, headImg=[18, 49, 35, 18, 48], createTime=Fri Apr 13 21:12:47 BOT 2018] 2018-04-21 19:46:52,699 INFO [main] (UserMapperTest.java:561) - ======2. 模拟不传id,但是传入了正确的 userName====== 2018-04-21 19:46:52,700 DEBUG [main] (BaseJdbcLogger.java:145) - ==> Preparing: SELECT a.id, a.user_name userName, a.user_password userPassword, a.user_email userEmail, a.user_info userInfo, a.head_img headImg, a.create_time createTime FROM sys_user a WHERE 1=1 and user_name = ? 2018-04-21 19:46:52,701 DEBUG [main] (BaseJdbcLogger.java:145) - ==> Parameters: admin(String) 2018-04-21 19:46:52,702 TRACE [main] (BaseJdbcLogger.java:151) - <== Columns: id, userName, userPassword, userEmail, userInfo, headImg, createTime 2018-04-21 19:46:52,702 TRACE [main] (BaseJdbcLogger.java:151) - <== Row: 1, admin, 123456, admin@artisan.com, <<BLOB>>, <<BLOB>>, 2018-04-13 21:12:47.0 2018-04-21 19:46:52,703 DEBUG [main] (BaseJdbcLogger.java:145) - <== Total: 1 2018-04-21 19:46:52,706 INFO [main] (UserMapperTest.java:571) - SysUser [id=1, userName=admin, userPassword=123456, userEmail=admin@artisan.com, userInfo=管理员用户, headImg=[18, 49, 35, 18, 48], createTime=Fri Apr 13 21:12:47 BOT 2018] 2018-04-21 19:46:52,706 INFO [main] (UserMapperTest.java:573) - ======3.什么都不传====== 2018-04-21 19:46:52,707 DEBUG [main] (BaseJdbcLogger.java:145) - ==> Preparing: SELECT a.id, a.user_name userName, a.user_password userPassword, a.user_email userEmail, a.user_info userInfo, a.head_img headImg, a.create_time createTime FROM sys_user a WHERE 1=1 and 1 = 2 2018-04-21 19:46:52,707 DEBUG [main] (BaseJdbcLogger.java:145) - ==> Parameters: 2018-04-21 19:46:52,709 DEBUG [main] (BaseJdbcLogger.java:145) - <== Total: 0 2018-04-21 19:46:52,709 INFO [main] (UserMapperTest.java:581) - 2018-04-21 19:46:52,712 INFO [main] (UserMapperTest.java:587) - sqlSession close successfully
注意观察每个条件匹配的SQL语句
