概述
MyBatis注解方式是将SQL直接注解写在接口上 。 这种方式的优点是对于需求比较简单的系统，效率较高。 缺点是：当SQL有变化时都需要重新编译代码。
一般情况下不建议使用注解的方式。这里仅仅演示下简单的用法，不深究。
@Select注解
使用注解的方式同样需要考虑表字段和Java属性字段映射的问题。我们现在看下通过注解如何完成这项工作
我们以通过Id查询所属的角色为例
通过数据库字段别名方式映射到实体类属性
1. RoleMapper接口增加接口方法，同时标注注解
/** * * * @Title: selectSysRoleById * * @Description: 采用数据库字段别名和实体类属性同名的方式映射 * * @param roleId * @return * * @return: SysRole */ @Select({ "SELECT " + " a.id, " + " a.role_name roleName, " + " a.enabled, " + " a.create_by createBy, " + " a.create_time createTime " + " FROM " + " sys_role a " + " WHERE " + " a.id = #{roleId}" }) SysRole selectSysRoleById(Long roleId);
2.单元测试
@Test public void selectSysRoleByIdTest() { logger.info("selectSysRoleByIdTest"); try { // 获取SqlSession sqlSession = getSqlSession(); // 获取接口 RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class); // 调用接口方法 SysRole sysRole = roleMapper.selectSysRoleById((long) 1); // 期待不为空 Assert.assertNotNull(sysRole); // 期望为 roleName="管理员" Assert.assertEquals("管理员", sysRole.getRoleName()); logger.info("sysRole Info:" + sysRole); } finally { sqlSession.close(); } }
日志
2018-04-17 21:37:36,996 INFO [main] (BaseMapperTest.java:26) - sessionFactory bulit successfully 2018-04-17 21:37:37,001 INFO [main] (BaseMapperTest.java:29) - reader close successfully 2018-04-17 21:37:37,006 INFO [main] (RoleMapperTest.java:19) - selectSysRoleByIdTest 2018-04-17 21:37:37,528 DEBUG [main] (BaseJdbcLogger.java:142) - ==> Preparing: SELECT a.id, a.role_name roleName, a.enabled, a.create_by createBy, a.create_time createTime FROM sys_role a WHERE a.id = ? 2018-04-17 21:37:37,607 DEBUG [main] (BaseJdbcLogger.java:142) - ==> Parameters: 1(Long) 2018-04-17 21:37:37,627 TRACE [main] (BaseJdbcLogger.java:148) - <== Columns: id, roleName, enabled, createBy, createTime 2018-04-17 21:37:37,627 TRACE [main] (BaseJdbcLogger.java:148) - <== Row: 1, 管理员, 1, 1, 2018-04-13 21:12:46.0 2018-04-17 21:37:37,629 DEBUG [main] (BaseJdbcLogger.java:142) - <== Total: 1 2018-04-17 21:37:37,632 INFO [main] (RoleMapperTest.java:32) - sysRole Info:SysRole [id=1, roleName=管理员, enabled=1, createBy=1, createTime=Fri Apr 13 21:12:46 BOT 2018, user=null, privilegeList=null]
通过mapUnderscoreToCamelCase完成数据库字段到实体类属性的映射
1.MyBatis全局文件settings节点增加如下配置
<!-- 通过配置这个属性为true可以自动将下画线方式命名的数据库列映射到java对象驼峰式命名属性中 --> <setting name="mapUnderscoreToCamelCase" value="true"/>
2. RoleMapper接口增加接口方法，同时标注注解
/** * * * @Title: selectSysRoleById2 * * @Description: 采用 MyBatis全局配置文件设置 mapUnderscoreToCamelCase 映射 * 通过配置这个属性为true可以自动将下画线方式命名的数据库列映射到java对象驼峰式命名属性中 * * @param roleId * @return * * @return: SysRole */ @Select({ "SELECT " + " a.id, " + " a.role_name , " + " a.enabled, " + " a.create_by , " + " a.create_time " + " FROM " + " sys_role a " + " WHERE " + " a.id = #{roleId}" }) SysRole selectSysRoleById2(Long roleId);
3.单元测试
/** * * * @Title: selectSysRoleByIdTest2 * * @Description: 测试的时候需要将 <setting name="mapUnderscoreToCamelCase" * value="true"/> 放开 * * * @return: void */ @Test public void selectSysRoleByIdTest2() { logger.info("selectSysRoleByIdTest2"); try { // 获取SqlSession sqlSession = getSqlSession(); // 获取接口 RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class); // 调用接口方法 SysRole sysRole = roleMapper.selectSysRoleById2((long) 2); // 期待不为空 Assert.assertNotNull(sysRole); // 期望为 roleName="普通用户" Assert.assertEquals("普通用户", sysRole.getRoleName()); logger.info("sysRole Info:" + sysRole); } finally { sqlSession.close(); } }
2018-04-17 21:38:57,518 INFO [main] (BaseMapperTest.java:26) - sessionFactory bulit successfully 2018-04-17 21:38:57,523 INFO [main] (BaseMapperTest.java:29) - reader close successfully 2018-04-17 21:38:57,526 INFO [main] (RoleMapperTest.java:51) - selectSysRoleByIdTest2 2018-04-17 21:38:58,057 DEBUG [main] (BaseJdbcLogger.java:142) - ==> Preparing: SELECT a.id, a.role_name , a.enabled, a.create_by , a.create_time FROM sys_role a WHERE a.id = ? 2018-04-17 21:38:58,139 DEBUG [main] (BaseJdbcLogger.java:142) - ==> Parameters: 2(Long) 2018-04-17 21:38:58,168 TRACE [main] (BaseJdbcLogger.java:148) - <== Columns: id, role_name, enabled, create_by, create_time 2018-04-17 21:38:58,169 TRACE [main] (BaseJdbcLogger.java:148) - <== Row: 2, 普通用户, 1, 1, 2018-04-13 21:12:46.0 2018-04-17 21:38:58,172 DEBUG [main] (BaseJdbcLogger.java:142) - <== Total: 1 2018-04-17 21:38:58,178 INFO [main] (RoleMapperTest.java:64) - sysRole Info:SysRole [id=2, roleName=普通用户, enabled=1, createBy=1, createTime=Fri Apr 13 21:12:46 BOT 2018, user=null, privilegeList=null]
通过@Results / @ReusltMap注解完成数据库字段到实体类属性的映射
XML中的resultMap元素有一个对应的JavaBean注解@Results,使用这个注解来实现属性映射。
1. RoleMapper接口增加接口方法，同时标注注解
/** * * * @Title: selectSysRoleById3 * * @Description: 通过ResultMap的方式实现数据库列到java对象的映射 * * @param roleId * @return * * @return: SysRole */ @Results({ @Result(property = "id", column = "id", id = true), @Result(property = "roleName", column = "role_name"), @Result(property = "enabled", column = "enabled"), @Result(property = "createBy", column = "create_by"), @Result(property = "createTime", column = "create_time") }) @Select({ "SELECT " + " a.id, " + " a.role_name , " + " a.enabled, " + " a.create_by , " + " a.create_time " + " FROM " + " sys_role a " + " WHERE " + " a.id = #{roleId}" }) SysRole selectSysRoleById3(Long roleId);
这里的@Result注解对应着xml文件中的<result>元素,而参数中协商id = true 时就对应 <id>元素
2.单元测试
@Test public void selectSysRoleByIdTest3() { logger.info("selectSysRoleByIdTest3"); try { // 获取SqlSession sqlSession = getSqlSession(); // 获取接口 RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class); // 调用接口方法 SysRole sysRole = roleMapper.selectSysRoleById3((long) 2); // 期待不为空 Assert.assertNotNull(sysRole); // 期望为 roleName="普通用户" Assert.assertEquals("普通用户", sysRole.getRoleName()); logger.info("sysRole Info:" + sysRole); } finally { sqlSession.close(); } }
2018-04-17 21:40:09,799 INFO [main] (BaseMapperTest.java:26) - sessionFactory bulit successfully 2018-04-17 21:40:09,803 INFO [main] (BaseMapperTest.java:29) - reader close successfully 2018-04-17 21:40:09,806 INFO [main] (RoleMapperTest.java:72) - selectSysRoleByIdTest3 2018-04-17 21:40:10,303 DEBUG [main] (BaseJdbcLogger.java:142) - ==> Preparing: SELECT a.id, a.role_name , a.enabled, a.create_by , a.create_time FROM sys_role a WHERE a.id = ? 2018-04-17 21:40:10,384 DEBUG [main] (BaseJdbcLogger.java:142) - ==> Parameters: 2(Long) 2018-04-17 21:40:10,412 TRACE [main] (BaseJdbcLogger.java:148) - <== Columns: id, role_name, enabled, create_by, create_time 2018-04-17 21:40:10,413 TRACE [main] (BaseJdbcLogger.java:148) - <== Row: 2, 普通用户, 1, 1, 2018-04-13 21:12:46.0 2018-04-17 21:40:10,416 DEBUG [main] (BaseJdbcLogger.java:142) - <== Total: 1 2018-04-17 21:40:10,421 INFO [main] (RoleMapperTest.java:85) - sysRole Info:SysRole [id=2, roleName=普通用户, enabled=1, createBy=1, createTime=Fri Apr 13 21:12:46 BOT 2018, user=null, privilegeList=null]
@Results的复用
MyBatis 3.3.0及以前版本中，注解定义的@Results不能共用，使用起来很不方便，需要再每个方法上都写一遍。
从MyBatis3.3.1版本开始，@Results注解增加了一个id属性，设置了i属性后，就可以通过id属性引用同一个@Reuslts配置了。
调整Mybatis版本
<mybatis.version>3.4.1</mybatis.version>
@Results(id = "roleResultMap", value = { @Result(property = "id", column = "id", id = true), @Result(property = "roleName", column = "role_name"), @Result(property = "enabled", column = "enabled"), @Result(property = "createTime", column = "create_time") })
如何引用呢？ 通过@ResultMap注解一弄
/** * * * @Title: selectSysRoleById4 * * @Description: 通过改方法演示在mybatis3.3.1版本及其之后的版本 通过@ResultMap应用带有id的@Results * * @param roleId * @return * * @return: SysRole */ @ResultMap("roleResultMap") @Select({ "SELECT a.id, a.role_name, a.enabled, a.create_by , a.create_time FROM sys_role a " }) List<SysRole> selectAllSysRole();
单元测试
@Test public void selectAllSysTest() { logger.info("selectAllSysTest"); try { // 获取SqlSession sqlSession = getSqlSession(); // 获取接口 RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class); // 调用接口方法 List<SysRole> sysRoleList = roleMapper.selectAllSysRole(); // 期待不为空 Assert.assertNotNull(sysRoleList); // 期望为sysRoleList > 0 Assert.assertTrue(sysRoleList.size() > 0); for (SysRole sysRole2 : sysRoleList) { logger.info("sysRole Info:" + sysRole2); } } finally { sqlSession.close(); } }
日志
2018-04-17 21:57:03,655 INFO [main] (BaseMapperTest.java:26) - sessionFactory bulit successfully 2018-04-17 21:57:03,659 INFO [main] (BaseMapperTest.java:29) - reader close successfully 2018-04-17 21:57:03,662 INFO [main] (RoleMapperTest.java:95) - selectAllSysTest 2018-04-17 21:57:04,159 DEBUG [main] (BaseJdbcLogger.java:145) - ==> Preparing: SELECT a.id, a.role_name, a.enabled, a.create_by , a.create_time FROM sys_role a 2018-04-17 21:57:04,249 DEBUG [main] (BaseJdbcLogger.java:145) - ==> Parameters: 2018-04-17 21:57:04,295 TRACE [main] (BaseJdbcLogger.java:151) - <== Columns: id, role_name, enabled, create_by, create_time 2018-04-17 21:57:04,296 TRACE [main] (BaseJdbcLogger.java:151) - <== Row: 1, 管理员, 1, 1, 2018-04-13 21:12:46.0 2018-04-17 21:57:04,299 TRACE [main] (BaseJdbcLogger.java:151) - <== Row: 2, 普通用户, 1, 1, 2018-04-13 21:12:46.0 2018-04-17 21:57:04,300 DEBUG [main] (BaseJdbcLogger.java:145) - <== Total: 2 2018-04-17 21:57:04,307 INFO [main] (RoleMapperTest.java:109) - sysRole Info:SysRole [id=1, roleName=管理员, enabled=1, createBy=1, createTime=Fri Apr 13 21:12:46 BOT 2018, user=null, privilegeList=null] 2018-04-17 21:57:04,307 INFO [main] (RoleMapperTest.java:109) - sysRole Info:SysRole [id=2, roleName=普通用户, enabled=1, createBy=1, createTime=Fri Apr 13 21:12:46 BOT 2018, user=null, privilegeList=null]
小结
@Select基本的用法我们就说到这里， 接下来看@insert注解
