MyBatisPlus的基本使用之QueryWrapper

QueryWrapper是MyBatis-Plus中的一个查询封装类，用于构建带有条件的查询语句。

1. QueryWrapper

使用普通的方式来设置查询条件，而不是使用Lambda表达式。

一系列方法设置查询条件。手动指定数据库表的列名作为方法的参数
- select 设置查询的字段
- eq、ne、gt、ge、lt、le 设置等于、不等于、大于、大于等于、小于、小于等于。
- orderBy 排序方式
- last 自定义SQL语句

2.区别

LambdaQueryChainWrapper使用Lambda表达式来设置查询条件，更加直观和类型安全
-而QueryWrapper使用普通方式来设置查询条件，更加灵活和通用

3.代码示例

package com.example.demo.mybatisplus.service;import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.conditions.update.UpdateWrapper;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.example.demo.zmybatisplus.entity.User;
import com.example.demo.zmybatisplus.mapper.UserMapper;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;@SpringBootTest
public class UserTest {@Autowiredprivate UserMapper userMapper;//----------------------------------  查询 ---------------------------------------------------//简单查询@Testpublic void testSelect() {//所有List<User> userList = userMapper.selectList(null);userList.forEach(System.out::println);//多个List<User> userList2 = userMapper.selectBatchIds(Arrays.asList(1L,2L,3L));userList2.forEach(System.out::println);//单个User user3 = userMapper.selectById(1L);System.out.println(user3);}//等值条件查询，-- HashMap@Testpublic void testSelectByMap() {HashMap<String, Object> map = new HashMap<>();//定义查询条件map.put("name", "小垃圾"); //where k = vmap.put("age",0);List<User> users = userMapper.selectByMap(map);users.forEach(System.out::println);}//Wrapper查询---1.数字的比较 2.字符串的模糊查询@Testpublic void testSelectByWrapper() {//链式调用构造查询条件QueryWrapper<User> queryWrapper=new QueryWrapper<>();queryWrapper.isNotNull("name").like("email","john").le("age",26).lt("version",2).orderByAsc("id","age");//选择API执行queryList<User> users = userMapper.selectList(queryWrapper);users.forEach(System.out::println);//        eq相等   ne不相等，   gt大于，    lt小于         ge大于等于       le 小于等于//        equal/ not equal/ greater than/ less than/ less than or equal/ great than or equal///模糊查询 like  notLike  likeLeft（%x）  likeRight   notLikeLeft  notLikeRight}//Wrapper查询---1. 查询区间内的记录  between//              2.集合  in （in  notIn）（inSql   notInSql）@Testvoid test2SelectByWrapper(){//查询区间内的记录  betweenQueryWrapper<User> wrapper = new QueryWrapper<>();wrapper.isNotNull("name").between("age",20,30);Long count = userMapper.selectCount(wrapper);System.out.println("count = " + count);//集合IN ： in  notInQueryWrapper<User> queryWrapper=new QueryWrapper<>();queryWrapper.in("id",Arrays.asList(1L,2L,3L,4L));Long c=userMapper.selectCount(queryWrapper);System.out.println("count="+c);// 集合  IN ( sql语句 )  :  inSql   notInSql//例: inSql("age", "1,2,3,4,5,6")--->age in (1,2,3,4,5,6)//例: inSql("id", "select id from table where id < 3")--->id in (select id from table where id < 3)QueryWrapper<User> queryWrapper2=new QueryWrapper<>();//queryWrapper2.inSql("id","1,2,3,4");//两种写法queryWrapper2.inSql("id","select id from user where id<=4");Long c2=userMapper.selectCount(queryWrapper);System.out.println("count="+c2);}//Wrapper查询---分组查询 groupBy  having@Testpublic void testGroupByByWrapper(){QueryWrapper<User> wrapper=new QueryWrapper<>();wrapper.select("version","sum(age) as num").groupBy("version").having("sum(age)>0").orderByDesc("num");//使用Map获取返回结果List<Map<String,Object>> list=userMapper.selectMaps(wrapper);list.forEach(System.out::println);}//Wrapper更新---@Testpublic void testUpdateWrapper() {//修改--所有的记录//        //方式1
//        UpdateWrapper<User> updateWrapper=new UpdateWrapper<>();
//        updateWrapper.set("name","updateName").set("email",null);
//        userMapper.update(updateWrapper);
//
//        //方式2
//        String sql = "name = 'updateName1', email = null ";
//        int affectedRows = userMapper.update(new UpdateWrapper<User>().setSql(sql));
//        System.out.println("Affected rows: " + affectedRows);//修改 -- id=1的记录  UpdateWrapper拥有 QueryWrapper一样的条件方法UpdateWrapper<User> updateWrapper2 = new UpdateWrapper<>();updateWrapper2.set("name", "updateName111").set("email", "人文氛围v给xxx@123.cpm").eq("id", 1);userMapper.update(null, updateWrapper2);}//分页查询@Testpublic void testPage() {Page<User> page = new Page<>(2,5); //开启拦截器后，会注册一个page对象  当前页，每页条数//方法源码：   <P extends IPage<T>> P selectPage(P page, @Param(Constants.WRAPPER) Wrapper<T> queryWrapper);userMapper.selectPage(page,null); //分页查询page.getRecords().forEach(System.out::println); //获取分页后的数据 打印System.out.println(page.getTotal()); //获取记录总数}//链式查询:  使用 Lambda 表达式的链式查询对象/*public List<User> getUserListByQueryWrapper() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.eq("age", 25).like("name", "John").orderByDesc("create_time");List<User> userList = userMapper.selectList(queryWrapper);return userList;}public List<User> getUserListByLambdaQueryChainWrapper() {LambdaQueryChainWrapper<User> lambdaQueryWrapper = new LambdaQueryChainWrapper<>(userMapper);lambdaQueryWrapper.eq(User::getAge, 25).like(User::getName, "John").orderByDesc(User::getCreateTime);List<User> userList = lambdaQueryWrapper.list();return userList;}public List<User> getUserListByLambdaQueryChainWrapperWithPage(int pageNum, int pageSize) {LambdaQueryChainWrapper<User> lambdaQueryWrapper = new LambdaQueryChainWrapper<>(userMapper);lambdaQueryWrapper.eq(User::getAge, 25).like(User::getName, "John").orderByDesc(User::getCreateTime).page(new Page<>(pageNum, pageSize));List<User> userList = lambdaQueryWrapper.list();return userList;}*///---------------------------增删改-查-------------------------------------------//加入了逻辑删除之后，查询会自动增加 delfalg=0;@Testpublic void testSelectById() {System.out.println("----- selectById method test -----");User user = userMapper.selectById(1L);Assertions.assertNotNull(user);System.out.println(user);}@Testpublic void testInsert() {System.out.println("----- insert method test -----");User user = new User();user.setName("John 雪花算法");user.setAge(25);user.setEmail("john.doe@example.com");int result = userMapper.insert(user);Assertions.assertEquals(1, result);System.out.println("Inserted user ID: " + user.getId());}@Testpublic void testUpdateById() {System.out.println("----- updateById method test -----");User user = new User();user.setId(1L);user.setAge(0);//update注解优先自定义设值int result = userMapper.updateById(user);Assertions.assertEquals(1, result);}//配置了全局逻辑删除 delfalg=0;@Testpublic void testDeleteById() {System.out.println("----- deleteById method test -----");int result = userMapper.deleteById(5L);Assertions.assertEquals(1, result);int r=userMapper.deleteBatchIds(Arrays.asList(1L,2L,3L));}//-------------------------- 乐观锁     ---------------------------------/*乐观锁（OptimisticLockerInnerInterceptor）机制:当要更新一条记录的时候，希望这条记录没有被别人更新乐观锁实现方式：
取出记录时，获取当前version
更新时，带上这个version
执行更新时， set version = newVersion where version = oldVersion
如果version不对，就更新失败*/@Test//乐观锁测试public void testOptimisticLocker(){//1、查询用户信息User user = userMapper.selectById(1L);//2、修改用户信息user.setEmail("123@qq.com");user.setName("小垃圾");//3、更新操作userMapper.updateById(user);  //WHERE id=? AND version=?}@Testpublic void testOptimisticLocker2(){//模拟多线程User user = userMapper.selectById(2L);user.setEmail("111jdw@qq.com");user.setName("帅小伙111");//我们在这里对线程1修改值//线程2插队User user2 = userMapper.selectById(2L);user2.setEmail("222jdw@qq.com");user2.setName("帅小伙222");userMapper.updateById(user2); //线程2抢先提交userMapper.updateById(user);//线程1失败，乐观锁在这种情况下防止了脏数据存在，没有乐观锁就会有覆盖掉线程2的操作}}