文章目录
- 1. 描述
- 1.1 MybatisPlusInterceptor
- 1.2 InnerInterceptor
- 2. 实现
- 2.1 不带条件的分页查询
- 2.2 带条件的分页查询
- 2.3 简述Page类
- 3. 注意事项
- 3.1 UncategorizedSQLException异常
- 3.2 不做记录总数的统计
1. 描述
1.1 MybatisPlusInterceptor
我们在开发的过程中,经常会遇到分页操作,其分为逻辑分页和物理分页,具体可参考我的博文:逻辑分页和物理分页
如果你用的是Mybatis-Plus
框架,可用MybatisPlusInterceptor
按如下配置分页代码:
@Configuration
public class MybatisPlusConfig {
@Bean
public MybatisPlusInterceptor mybatisPlusInterceptor() {
MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
return interceptor;
}
}
如果你用的是低版本
的spring boot
,可用PaginationInterceptor
按如下配置:
@Configuration
public class MybatisPlusConfig {
@Bean
public PaginationInterceptor paginationInterceptor() {
return new PaginationInterceptor();
}
}
MybatisPlusInterceptor
插件是核心插件,目前代理了Executor#query、Executor#update、StatementHandler#prepare
方法,其属性:
private List<InnerInterceptor> interceptors = new ArrayList<>();
1.2 InnerInterceptor
注意List<InnerInterceptor>
泛型中的InnerInterceptor
,mybatis-plus
提供的插件都将基于此接口来实现功能,目前已有的功能如下:
-
自动分页: PaginationInnerInterceptor
-
多租户:TenantLineInnerInterceptor
-
动态表名:DynamicTableNameInnerInterceptor
-
乐观锁:OptimisticLockerInnerInterceptor
-
sql性能规范: IllegalSQLInnerInterceptor
-
防止全表更新与删除: BlockAttackInnerInterceptor
【注意】使用多个功能需要注意顺序关系,建议使用如下顺序:
-
多租户
-
动态表名
-
分页,乐观锁
-
sql
性能规范,防止全表更新与删除
总结:对sql
进行单次改造的优先放入,不对sql
进行改造的最后放入。
2. 实现
2.1 不带条件的分页查询
- 编写查询展示类
@NoArgsConstructor
@Data
@ApiModel(description = "用户返回结果")
public class UserPageVo {
@ApiModelProperty(name = "username", value = "用户名")
private String username;
@ApiModelProperty(name = "nickname", value = "昵称")
private String nickname;
@ApiModelProperty(name = "userType", value = "用户类型")
private String userType;
}
- 编写
mapper
类
@Mapper
public interface UserMapper extends BaseMapper<User> {
@Select("select " +
"username,nickname,user_type as userType " +
"from " +
"user " +
"order by " +
"create_time desc"
)
List<UserPageVo> findPageUsers(Page<UserPageVo> page);
}
- 编写
service
类
@Service
public class UserService extends ServiceImpl<UserMapper, User> {
@Resource private UserMapper userMapper;
public Page<UserPageVo> findPageUsers() {
Long currentPage = 4L;
Long pageSize = 3L;
Page<UserPageVo> page = new Page<>(currentPage, pageSize);
List<UserPageVo> pageUsers = userMapper.findPageUsers(page);
page.setRecords(pageUsers);
return page;
}
}
- 编写
controller
类
@Api(tags = "用户模块")
@RestController
@RequestMapping("/user")
@Slf4j
@Validated
public class UserController {
@Autowired private UserService userService;
@ApiOperationSupport(author = "念兮为美")
@ApiOperation(value = "用户查询接口")
@GetMapping("/findPageUsers")
public Page<UserPageVo> findPageUsers() {
return userService.findPageUsers();
}
}
- 测试运行结果
JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@2ce7d43] will not be managed by Spring
==> Preparing: SELECT COUNT(*) AS total FROM user
==> Parameters:
<== Columns: total
<== Row: 24
<== Total: 1
==> Preparing: select username,nickname,user_type as userType from user order by create_time desc LIMIT ?,?
==> Parameters: 9(Long), 3(Long)
<== Columns: username, nickname, userType
<== Row: cs, null, admin
<== Row: lin, null, admin
<== Row: test3, null, TEST4
<== Total: 3
2.2 带条件的分页查询
public class UserService extends ServiceImpl<UserMapper, User> {
@Resource private UserMapper userMapper;
public Page<User> findPageUsers() {
Long currentPage = 1L;
Long pageSize = 3L;
Page<User> page = new Page<>(currentPage, pageSize);
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.eq("username", "test5");
Page<User> userPage = userMapper.selectPage(page, queryWrapper);
return userPage;
}
运行结果:
JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@475454ae] will not be managed by Spring
==> Preparing: SELECT COUNT(*) AS total FROM user WHERE deleted = false AND (username = ?)
==> Parameters: test2(String)
<== Columns: total
<== Row: 1
<== Total: 1
==> Preparing: SELECT username,nickname,user_type FROM user WHERE deleted=false AND (username = ?) LIMIT ?
==> Parameters: test2(String), 3(Long)
<== Columns: username, nickname, user_type
<== Row: test2, null,TEST6
<== Total: 1
2.3 简述Page类
简单分页模型, 有如下几个主要属性
protected List<T> records = Collections.emptyList();
protected long total = 0;
protected long size = 10;
protected long current = 1;
3. 注意事项
3.1 UncategorizedSQLException异常
在编写mapper.xml
中的SQL
语句时,或者使用@select
注解编写SQL
语句时,语句末尾不能使用 ;
结尾,原因是在做分页的时候会在编写的SQL
语句后面拼接上limit
语句, 导致出现SQL
语法错误(UncategorizedSQLException
)。
可以参考我的这篇博文:全网最详细的org.springframework.jdbc.UncategorizedSQLException的多种解决方法
3.2 不做记录总数的统计
new Page(queryParam.getCurrent(), queryParam.getSize())
的两个参数表示:当前页和每页数量
如果业务需求只需要查询分页做上下页切换而不需要记录总数,可以设置第三个参数false
就可以不查询count()
,以提高性能,即new Page(queryParam.getCurrent(), queryParam.getSize(), false)
,如下代码所示:
@Service
public class UserService extends ServiceImpl<UserMapper, User> {
@Resource private UserMapper userMapper;
public Page<UserPageVo> findPageUsers() {
Long currentPage = 4L;
Long pageSize = 3L;
Page<UserPageVo> page = new Page<>(currentPage, pageSize, false);
List<UserPageVo> pageUsers = userMapper.findPageUsers(page);
page.setRecords(pageUsers);
return page;
}
从输出结果看,既没有count
操作,如下所示:
JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@466c39de] will not be managed by Spring
==> Preparing: select username,nickname,user_type as userType from user order by create_time desc LIMIT ?,?
==> Parameters: 9(Long), 3(Long)
<== Columns: username, nickname, userType
<== Row: cs, null, admin
<== Row: lin, null, admin
<== Row: test3, null, TEST4
<== Total: 3
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