1 配置分页插件
@Configuration
public class MybatisConfig {
@Bean
public PaginationInterceptor paginationInterceptor() {
return new PaginationInterceptor();
}
}
在高版本的SpringBoot中, 会提示这种写法已过时, 所以采用另一种写法 MybatisPlusInterceptor , 如下:
@Bean
public MybatisPlusInterceptor mybatisPlusInterceptor() {
MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.H2));
return interceptor;
}
1.1 MybatisPlusInterceptor
该插件是核心插件,目前代理了 Executor#query 和 Executor#update 和 StatementHandler#prepare 方法
1.1.1 属性
private List<InnerInterceptor> interceptors = new ArrayList<>();
1.1.2 InnerInterceptor
我们提供的插件都将基于此接口来实现功能 目前已有的功能: 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 编写Mapper及其对应的mapper.xml文件
@Mapper
public interface UserMapper extends BaseMapper<User> {
List<User> findPageUsers(Page<User> page);
}
<select id="findPageUsers" resultType="org.wxmx.mybatis_plus_study.entity.User">
select *
from `user`
</select>
3 编写测试类
3.1 简单的分页查询
@SpringBootTest
class MybatisPlusStudyApplicationTests {
@Resource
UserMapper userMapper;
@Test
void contextLoads() {
Page<User> page = new Page<>(1, 3);
List<User> pageUsers = userMapper.findPageUsers(page);
page.setRecords(pageUsers);
System.out.println(page);
}
}
运行结果:
JsqlParserCountOptimize sql=select *
from `user`
==> Preparing: SELECT COUNT(1) FROM `user`
==> Parameters:
<== Columns: COUNT(1)
<== Row: 9
==> Preparing: select * from `user` LIMIT ?
==> Parameters: 3(Long)
<== Columns: id, name, age
<== Row: 39a773890a1b12b8a072c1be02ff3cdc, aaa, 12
<== Row: 3b25fb904548c28b7ac6882d86c7ae5f, wdh, 12
<== Row: 8b0397fcdfebe37d1d26175c17ed3725, wdh, 12
<== Total: 3
3.2 带查询条件的分页查询
此方法是使用PaginationInterceptor 作为分页插件.
@Test
void contextLoads() {
Page<User> page = new Page<>(1, 2);
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.eq("name", "wdh");
Page<User> page1 = userMapper.selectPage(page, queryWrapper);
page.setRecords(page1.getRecords()).getRecords().forEach(System.out::println);
}
运行结果:
JsqlParserCountOptimize sql=SELECT id,name,age FROM user
WHERE (name = ?)
==> Preparing: SELECT COUNT(1) FROM user WHERE (name = ?)
==> Parameters: wdh(String)
<== Columns: COUNT(1)
<== Row: 5
==> Preparing: SELECT id,name,age FROM user WHERE (name = ?) LIMIT ?
==> Parameters: wdh(String), 2(Long)
<== Columns: id, name, age
<== Row: 3b25fb904548c28b7ac6882d86c7ae5f, wdh, 12
<== Row: 8b0397fcdfebe37d1d26175c17ed3725, wdh, 12
<== Total: 2
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6a0f2853]
User(id=3b25fb904548c28b7ac6882d86c7ae5f, name=wdh, age=12)
User(id=8b0397fcdfebe37d1d26175c17ed3725, name=wdh, age=12)
3.3 Page
简单分页模型, 有如下几个主要属性
/**
* 查询数据列表
*/
protected List<T> records = Collections.emptyList();
/**
* 总数
*/
protected long total = 0;
/**
* 每页显示条数，默认 10
*/
protected long size = 10;
/**
* 当前页
*/
protected long current = 1;
4 注意事项
在编写mapper.xml中的SQL语句的时候, 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(SQLSyntaxErrorException). 如下所示:
JsqlParserCountOptimize sql=select *
from `user`;
==> Preparing: SELECT COUNT(1) FROM `user`
==> Parameters:
<== Columns: COUNT(1)
<== Row: 9
==> Preparing: select * from `user`; LIMIT ?
==> Parameters: 3(Long)
org.springframework.jdbc.BadSqlGrammarException:
### Error querying database. Cause: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'LIMIT 3' at line 1
### The error may exist in org/wxmx/mybatis_plus_study/mapper/UserMapper.xml
### The error may involve defaultParameterMap
### The error occurred while setting parameters
### SQL: select * from `user`; LIMIT ?
### Cause: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'LIMIT 3' at line 1
; bad SQL grammar []; nested exception is java.sql.SQLSyntaxErrorException: You have an error in your SQL