目录

语法展示

基础的增删改查

分页查询

语法指导

删除操作

条件操作

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语法展示

@Mapper
public interface UserMapper extends BaseMapper<User> {}

public interface UserService extends IService<User> {}

@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {@Autowiredprivate UserMapper userMapper;
}

@RestController
@RequestMapping("/test/user")
public class UserController {@Autowiredprivate UserService userService;
}

基础的增删改查

查询所有，参数为构造器 : userMapper.selectList(null) 根据id添加数据，参数为实体类对象：  userMapper.insert(user);根据id修改数据，参数为实体类对象:   userMapper.updateById(user)根据id删除数据，参数为int / Long :  userMapper.deleteById(5L)根据id查询数据，餐位数int / Long ： userMapper.selectById(4L)

分页查询

  R<IPage<User>>  getUsersByNamec(Page<User> page, String name);

    @Overridepublic R<IPage<User>> getUsersByNamec(Page<User> page, String name) {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.like(StringUtils.isNotBlank(name), "name", name);return R.success(userMapper.selectPage(page, queryWrapper));}

    // 根据姓名分页查询用户@GetMapping("/getUsersByName")public IPage<User> getUsersByName(@RequestParam(defaultValue = "1") Long current,@RequestParam(defaultValue = "2") Long size,@RequestParam(required = false) String name) {// 构建分页对象Page<User> userpage = new Page<>(current, size);//返回对象得到分页所有数据long pages = userPage.getPages(); //总页数long current = userPage.getCurrent(); //当前页List<User> records = userPage.getRecords(); //查询数据集合long total = userPage.getTotal(); //总记录数boolean hasNext = userPage.hasNext();  //下一页boolean hasPrevious = userPage.hasPrevious(); //上一页// 调用服务方法进行分页查询return userService.getUsersByName(page, name);}

语法指导

* mp复杂查询* eq 就是 equal等于* ne就是 not equal不等于** gt 就是 greater than大于* ge 就是 greater than or equal 大于等于* lt 就是 less than小于* le 就是 less than or equal 小于等于** in 就是 in 包含（数组）* between 就是 在2个条件之间(包括边界值)* notBetween** isNull 就是 等于null* isNotNull 不等于** like 就是 模糊查询* notLike* likeLeft* likeRight** orderBy* orderByDesc* orderByAsc

删除操作

批量删除： userMapper.deleteBatchIds(Arrays.asList(8, 9, 10));简单删除://简单条件删除@Testpublic void testDeleteByMap() {HashMap<String, Object> map = new HashMap<>();//  name,age 为字段 ---> lucy,20 为值map.put("name", "lucy");map.put("age", 20);int result = userMapper.deleteByMap(map);System.out.println(result);}

条件操作

 // 查询年龄  > 21 的  public void testQuery() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.ge("age", 21);List<User> users = userMapper.selectList(queryWrapper);System.out.println(users);}// 查询name 是 Tom的@Testpublic void testSelectOne() {QueryWrapper<User>queryWrapper = new QueryWrapper<>();queryWrapper.eq("name", "Tom");User user = userMapper.selectOne(queryWrapper);//只能返回一条记录，多余一条则抛出异常System.out.println(user);}// 查询年龄在20 ~ 30之间的@Testpublic void testSelectCount() {QueryWrapper<User>queryWrapper = new QueryWrapper<>();queryWrapper.between("age", 20, 30);Integer count = userMapper.selectCount(queryWrapper); //返回数据数量System.out.println(count);}

查询条件构建： 使用 QueryWrapper 对象 queryWrapper 构建查询条件。在这个例子中，通过 .select("name", "age") 指定要查询的字段，.like("name", "e") 表示名字中包含字母 "e"，.likeRight("email", "5") 表示邮箱以数字 "5" 结尾。
 

    @Testpublic void testSelectMaps() {QueryWrapper<User>queryWrapper = new QueryWrapper<>();queryWrapper.select("name", "age").like("name", "y").likeRight("email", "5");List<Map<String, Object>>maps = userMapper.selectMaps(queryWrapper);//返回值是Map列表maps.forEach(System.out::println);}