MyBatis-Plus BaseMapper 中各个核心函数的使用示例及其对应的底层 SQL 语句

➕ 新增 (Insert)int insert(T entity)Java 示例User user new User(); user.setName(张三); user.setAge(25); user.setEmail(zhangsanexample.com); int result userMapper.insert(user);对应 SQLINSERT INTO user (name, age, email) VALUES (张三, 25, zhangsanexample.com);️ 删除 (Delete)int deleteById(Serializable id)Java 示例int result userMapper.deleteById(1L);对应 SQLDELETE FROM user WHERE id 1;int deleteById(T entity)Java 示例User user new User(); user.setId(1L); int result userMapper.deleteById(user);对应 SQLDELETE FROM user WHERE id 1;本质仍是提取实体中的主键ID进行删除default int deleteByMap(MapString, Object columnMap)Java 示例MapString, Object map new HashMap(); map.put(name, 张三); map.put(age, 25); int result userMapper.deleteByMap(map);对应 SQLDELETE FROM user WHERE name 张三 AND age 25;int delete(Param(ew) WrapperT queryWrapper)Java 示例QueryWrapperUser wrapper new QueryWrapper(); wrapper.eq(age, 25); int result userMapper.delete(wrapper);对应 SQLDELETE FROM user WHERE age 25;int deleteBatchIds(Param(coll) Collection? idList)Java 示例ListLong ids Arrays.asList(1L, 2L, 3L); int result userMapper.deleteBatchIds(ids);对应 SQLDELETE FROM user WHERE id IN (1, 2, 3);✏️ 修改 (Update)int updateById(Param(et) T entity)Java 示例User user new User(); user.setId(1L); user.setEmail(newemailexample.com); // 只更新不为null的字段 int result userMapper.updateById(user);对应 SQLUPDATE user SET email newemailexample.com WHERE id 1;int update(Param(et) T entity, Param(ew) WrapperT updateWrapper)Java 示例UpdateWrapperUser wrapper new UpdateWrapper(); wrapper.eq(name, 张三); User user new User(); user.setEmail(zhangsan_updatedexample.com); int result userMapper.update(user, wrapper);对应 SQLUPDATE user SET email zhangsan_updatedexample.com WHERE name 张三;default int update(Param(ew) WrapperT updateWrapper)Java 示例UpdateWrapperUser wrapper new UpdateWrapper(); wrapper.set(age, 30).eq(name, 张三); // 直接在Wrapper中设置要更新的值 int result userMapper.update(null, wrapper);对应 SQLUPDATE user SET age 30 WHERE name 张三; 查询 (Select)T selectById(Serializable id)Java 示例User user userMapper.selectById(1L);对应 SQLSELECT id, name, age, email FROM user WHERE id 1;ListT selectBatchIds(...)Java 示例ListLong ids Arrays.asList(1L, 2L, 3L); ListUser userList userMapper.selectBatchIds(ids);对应 SQLSELECT id, name, age, email FROM user WHERE id IN (1, 2, 3);void selectBatchIds(..., ResultHandlerT resultHandler)Java 示例ListLong ids Arrays.asList(1L, 2L, 3L); userMapper.selectBatchIds(ids, resultContext - { User user resultContext.getResultObject(); System.out.println(流式处理用户 user.getName()); });对应 SQLSELECT id, name, age, email FROM user WHERE id IN (1, 2, 3);通过流式游标逐条拉取结果避免一次性加载到内存用时间换空间的策略虽然整体处理时长可能会稍微增加因为存在多次网络交互但它保证了系统在面临海量数据冲击时依然能够稳定运行不会崩default ListT selectByMap(MapString, Object columnMap)Java 示例MapString, Object map new HashMap(); map.put(age, 25); ListUser userList userMapper.selectByMap(map);对应 SQLSELECT id, name, age, email FROM user WHERE age 25;default void selectByMap(..., ResultHandlerT resultHandler)Java 示例MapString, Object map new HashMap(); map.put(age, 25); userMapper.selectByMap(map, resultContext - { System.out.println(流式处理用户 resultContext.getResultObject().getName()); });对应 SQLSELECT id, name, age, email FROM user WHERE age 25;default T selectOne(...)Java 示例QueryWrapperUser wrapper new QueryWrapper(); wrapper.eq(name, 张三).last(LIMIT 1); User user userMapper.selectOne(wrapper);对应 SQLSELECT id, name, age, email FROM user WHERE name 张三 LIMIT 1;default boolean exists(WrapperT queryWrapper)Java 示例QueryWrapperUser wrapper new QueryWrapper(); wrapper.eq(name, 张三); boolean isExists userMapper.exists(wrapper);对应 SQLSELECT COUNT(*) FROM user WHERE name 张三;判断返回的数量是否大于 0Long selectCount(Param(ew) WrapperT queryWrapper)Java 示例QueryWrapperUser wrapper new QueryWrapper(); wrapper.gt(age, 20); Long count userMapper.selectCount(wrapper);对应 SQLSELECT COUNT(*) FROM user WHERE age 20;ListT selectList(...)Java 示例QueryWrapperUser wrapper new QueryWrapper(); wrapper.ge(age, 18); ListUser userList userMapper.selectList(wrapper);对应 SQLSELECT id, name, age, email FROM user WHERE age 18;void selectList(..., ResultHandlerT resultHandler)Java 示例QueryWrapperUser wrapper new QueryWrapper(); wrapper.ge(age, 18); userMapper.selectList(wrapper, resultContext - { System.out.println(resultContext.getResultObject().getName()); });对应 SQLSELECT id, name, age, email FROM user WHERE age 18;ListT selectList(IPageT page, ...)Java 示例PageUser page new Page(1, 10); // 第1页每页10条 QueryWrapperUser wrapper new QueryWrapper(); IPageUser userPage userMapper.selectList(page, wrapper);