QueryWrapper，LambdaQueryWrapper用法简介（MyBatis Plus进阶）
目录
- 一、项目结构及数据库内容如图
- 二、数据库内容
- 三、代码示例
关于如何使用MyBatis Plus自动生成service，mapper，domain参考我的这篇博客使用MyBatis Plus自动生成service，mapper，domain
一、项目结构及数据库内容如图
service，mapper，domain均为MyBatis Plus自动生成。
二、数据库内容
create table mp.tb_user
(
id bigint auto_increment comment '主键ID'
primary key,
user_name varchar(20) not null comment '用户名',
password varchar(20) not null comment '密码',
name varchar(30) null comment '姓名',
age int null comment '年龄',
email varchar(50) null comment '邮箱',
dept_id int null,
salary double null
)
charset = utf8;
INSERT INTO mp.tb_user (id, user_name, password, name, age, email, dept_id, salary) VALUES (1, 'zhangsan', '123456', '张三', 18, '[email protected]', 222, 2000);
INSERT INTO mp.tb_user (id, user_name, password, name, age, email, dept_id, salary) VALUES (2, 'lisi', '123456', '李四', 20, '[email protected]', 333, 3000);
INSERT INTO mp.tb_user (id, user_name, password, name, age, email, dept_id, salary) VALUES (3, 'wangwu', '123456', '王五', 28, '[email protected]', 222, 4000);
INSERT INTO mp.tb_user (id, user_name, password, name, age, email, dept_id, salary) VALUES (4, 'zhaoliu', '123456', '赵六', 21, '[email protected]', 333, 5000);
INSERT INTO mp.tb_user (id, user_name, password, name, age, email, dept_id, salary) VALUES (5, 'sunqi', '123456', '孙七', 24, '[email protected]', 222, 2000);
INSERT INTO mp.tb_user (id, user_name, password, name, age, email, dept_id, salary) VALUES (6, 'sajkdl', '123456', 'sajkdl', 18, '[email protected]', 222, 4000);
INSERT INTO mp.tb_user (id, user_name, password, name, age, email, dept_id, salary) VALUES (7, 'dkfldk', '123456', 'dkfldk', 20, '[email protected]', 333, 3000);
INSERT INTO mp.tb_user (id, user_name, password, name, age, email, dept_id, salary) VALUES (8, 'rpewp', '123456', 'rpewp', 28, '[email protected]', 222, 2000);
INSERT INTO mp.tb_user (id, user_name, password, name, age, email, dept_id, salary) VALUES (9, 'ksjd', '123456', 'ksjd', 21, '[email protected]', 333, 2000);
INSERT INTO mp.tb_user (id, user_name, password, name, age, email, dept_id, salary) VALUES (10, 'kzzlk', '123456', 'kzzlk', 24, '[email protected]', 222, 3000);
INSERT INTO mp.tb_user (id, user_name, password, name, age, email, dept_id, salary) VALUES (11, 'weiro', '123456', 'weiro', null, '[email protected]', 222, 5000);
三、代码示例
下面是@Test注解的示例
package com.example.itcastmybatisplus;
import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.example.itcastmybatisplus.domain.TbUser;
import com.example.itcastmybatisplus.domain.query.UserQuery;
import com.example.itcastmybatisplus.mapper.TbUserMapper;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import java.util.List;
@SpringBootTest
class ItcastMybatisPlusApplicationTests {
@Test
void contextLoads() {
}
@Autowired private TbUserMapper userMapper;
// 测试函数
@Test public void A(){
List<TbUser> tbUsers = userMapper.selectList(null);
System.out.println(tbUsers);
}
// 条件查询 查找所有年龄<22岁的user
@Test public void B(){
QueryWrapper<TbUser> queryWrapper = new QueryWrapper<>();
queryWrapper.lt("age",22);
List<TbUser> tbUsers = userMapper.selectList(queryWrapper);
System.out.println(tbUsers);
}
//QueryWrapper的基础上使用lambda
@Test public void C(){
QueryWrapper<TbUser> queryWrapper = new QueryWrapper<>();
queryWrapper.lambda().lt(TbUser::getAge,22);
List<TbUser> tbUsers = userMapper.selectList(queryWrapper);
System.out.println(tbUsers);
}
// 查询年龄小于22岁的user
@Test public void D(){
LambdaQueryWrapper<TbUser> queryWrapper = new LambdaQueryWrapper<>();
queryWrapper.lt(TbUser::getAge,22);
List<TbUser> tbUsers = userMapper.selectList(queryWrapper);
System.out.println(tbUsers);
}
//条件查询，查询年龄在19岁以上，25岁一下的user
@Test public void E(){
LambdaQueryWrapper<TbUser> wrapper = new LambdaQueryWrapper<>();
wrapper.lt(TbUser::getAge,25);
wrapper.gt(TbUser::getAge,19);
List<TbUser> tbUsers = userMapper.selectList(wrapper);
System.out.println(tbUsers);
}
// 查询年龄小于20 '或者' 大于25岁的user
@Test public void F(){
LambdaQueryWrapper<TbUser> wrapper = new LambdaQueryWrapper<>();
wrapper.gt(TbUser::getAge,25).or().lt(TbUser::getAge,20);
System.out.println(userMapper.selectList(wrapper));
}
//比较的字段始终只有一个age，因此如果不注释uq.setAge(20);和uq.setAge(25);的话，就是选出age在20和25之间的
//如果注释uq.setAge(20);就是选出age<25的
//如果注释uq.setAge2(25);就是选出age>20的
@Test public void G(){
UserQuery uq = new UserQuery();
uq.setAge(20);
// uq.setAge2(25);
LambdaQueryWrapper<TbUser> wrapper = new LambdaQueryWrapper<>();
wrapper.lt(uq.getAge2()!=null,TbUser::getAge,uq.getAge2());
wrapper.gt(uq.getAge()!=null,TbUser::getAge,uq.getAge());
System.out.println(userMapper.selectList(wrapper));
}
// 查询投影,选择特定的字段输出，没选择的字段输出为NULL
@Test public void H(){
LambdaQueryWrapper<TbUser> wrapper = new LambdaQueryWrapper<>();
wrapper.select(TbUser::getId,TbUser::getUserName);
System.out.println(userMapper.selectList(wrapper));
}
// 聚合函数查询
@Test public void I(){
//不能使用LambdaQueryWrapper
QueryWrapper<TbUser> wrapper = new QueryWrapper<>();
wrapper.select("count(*) as cnt , max(age) as max_age");
// wrapper.select("max(age) as max_age");
System.out.println(userMapper.selectMaps(wrapper));
}
@Test public void J(){
QueryWrapper<TbUser> wrapper = new QueryWrapper<>();
// wrapper.select("count(*) as cnt , max(age) as max_age");
// wrapper.lambda().groupBy(TbUser::getDeptId);
wrapper.select("count(*) as count,email");
wrapper.groupBy("email");
System.out.println(userMapper.selectMaps(wrapper));
}
// 登录查询,等值查询
@Test public void K(){
LambdaQueryWrapper<TbUser> wrapper = new LambdaQueryWrapper<>();
wrapper.eq(TbUser::getUserName,"zhangsan").eq(TbUser::getPassword,"123456");
TbUser tbUser = userMapper.selectOne(wrapper);
System.out.println(tbUser);
}
// 范围查询,对年龄进行范围查询，使用lt()、le()、gt()、ge()、between()进行范围查询
// gt():大于(>)
// ge():大于等于(>=)
// lt():小于(<)
// lte():小于等于(<=)
// between():between ? and ?
@Test public void L(){
LambdaQueryWrapper<TbUser> wrapper = new LambdaQueryWrapper<>();
wrapper.between(TbUser::getAge,20,25);
System.out.println(userMapper.selectList(wrapper));
}
// :查询表中name属性的值以J开头的用户信息,使用like进行模糊查询
// like():前后加百分号,如 %J%
// likeLeft():前面加百分号,如 %J
// likeRight():后面加百分号,如 J%
@Test public void M(){
LambdaQueryWrapper<TbUser> wrapper = new LambdaQueryWrapper<>();
wrapper.likeRight(TbUser::getName,"s");
System.out.println(userMapper.selectList(wrapper));
System.out.println("--------------------------------------------------");
wrapper = new LambdaQueryWrapper<>();
wrapper.like(TbUser::getName,"s");
System.out.println(userMapper.selectList(wrapper));
}
@Test public void N(){
// orderBy排序
// condition:条件，true则添加排序，false则不添加排序
// isAsc:是否为升序，true升序，false降序
// columns:排序字段，可以有多个
LambdaQueryWrapper<TbUser> wrapper = new LambdaQueryWrapper<>();
wrapper.orderByAsc(TbUser::getSalary);
System.out.println(userMapper.selectList(wrapper));
System.out.println("--------------------------------------------------");
/**
* orderByAsc/Desc(单个column):按照指定字段进行升序/降序
* orderByAsc/Desc(多个column):按照多个字段进行升序/降序
* orderByAsc/Desc
* condition:条件，true添加排序，false不添加排序
* 多个columns：按照多个字段进行排序
*/
wrapper = new LambdaQueryWrapper<>();
wrapper.orderBy(true,false,TbUser::getSalary);
System.out.println(userMapper.selectList(wrapper));
}
}