条件构造器书写 MybatisPlus 复杂 SQL 语句

哈喽，大家好，我是指北君。
之前有一篇文章，我们介绍过通过 Mybatis Plus 进行增删改查。如下这段代码：

/**
 _ 根据 id 修改
 _ UPDATE user SET user_name=?, user_age=? WHERE (id = ?)
 */
@Test  
public void testudpateById(){
    User user = new User();
    user.setUserAge("25");
    user.setUserName("test update");
    UpdateWrapper updateWrapper = new UpdateWrapper();
    updateWrapper.eq("id","3");
    int num = userMapper.update(user, updateWrapper);
    System.out.println("修改的记录数为："+num);
}
/**
 _ 查询指定记录
 _ SELECT id,user_name,user_age FROM user WHERE (user_name = ?)
 */
@Test  
public void testSelectWrapper(){
    QueryWrapper wrapper = new QueryWrapper();
    wrapper.eq("user_name","IT 可乐");
    List users = userMapper.selectList(wrapper);
    users.forEach(x-> System.out.println(x.getId()+"-"+x.getUserName()+"-"+x.getUserAge()));
}

上面两个方法分别是根据 id 修改表记录，和根据 user_name 查询记录。构造的条件使用了 UpdateWrapper 和 QueryWrapper ，那么这是什么呢？其实 mybatis plus 通过条件构造器可以组成复杂的 SQL 语句。本篇博客我们将详细介绍。

1、Wrapper

Mybatis Plus 提供的几种条件构造器，关系如下：

我们主要通过 QueryWrapper 和 UpdateWrapper 进行条件构造，这两个和 LambdaQueryWrapper、LambdaUpdateWrapper 差不多是等价的，只不过后者采用了 JDK1.8 提供的 lambda 语法，使用起来更简洁。

2、语法详情总结

关于条件构造器的各个用法介绍，可以参考官网：https://mp.baomidou.com/guide/wrapper.html#abstractwrapper

这里我们做一下总结：

3、语法详情演示

对于上表出现的每个语法，这里通过代码展示出来。

更多可以参考地址：https://github.com/YSOcean/mybatisplusstudy.git

package com.ys.mybatisplusstudy;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.ys.mybatisplusstudy.entry.User;
import com.ys.mybatisplusstudy.mapper.UserMapper;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
@SpringBootTest  
public class WrapperTest {
    @Autowired  
    private UserMapper userMapper;
/**
     _ 新增一条记录
     _/
    @Test  
    public void testInsert(){
        User user = new User();
        user.setId(4L);
        user.setUserName("test insert");
        user.setUserAge("1");
        int insert = userMapper.insert(user);
        System.out.println("影响记录数："+insert);
    }
/**
     _ allEq 全部等于
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_name = ? AND id = ?)
     */
    @Test  
    public void testAllEq(){
        QueryWrapper queryWrapper = new QueryWrapper();
        Map map = new HashMap<>();
        map.put("id","3");
        map.put("user_name","IT 可乐");
        queryWrapper.allEq(map);
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ eq 等于
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (id = ?)
     */
    @Test  
    public void testEq(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.eq("id","3");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ ne 不等于
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (id <> ?)
     */
    @Test  
    public void testNe(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.ne("id","3");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ gt 大于
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_age> ?)
     */
    @Test  
    public void testGt(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.gt("user_age","18");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ ge 大于等于
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_age>= ?)
     */
    @Test  
    public void testGe(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.ge("user_age","18");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ lt 小于
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_age < ?)
     */
    @Test  
    public void testLt(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.lt("user_age","18");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ le 小于等于
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_age <= ?)
     */
    @Test  
    public void testLe(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.le("user_age","18");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ between 值 1 和值 2 之间, 两边临界值都包含
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_age BETWEEN ? AND ?)
     */
    @Test  
    public void testBetween(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.between("user_age","18","25");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ notBetween 不在值 1 和值 2 之间，两边临界值都包含
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_age NOT BETWEEN ? AND ?)
     */
    @Test  
    public void testNoBetween(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.notBetween("user_age","18","25");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ like 模糊查询，会在参数左右两边加上 %
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_name LIKE ?)
     */
    @Test  
    public void testLike(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.like("user_name","可乐");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ notLike NOT LIKE ‘%parameter%’
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_name NOT LIKE ?)
     */
    @Test  
    public void testNotLike(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.notLike("user_name","可乐");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ likeLeft LIKE ‘%parameter’
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_name LIKE '%parameter')
     */
    @Test  
    public void testLikeLeft(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.likeLeft("user_name","可乐");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ likeRight LIKE ‘parameter%’
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_name LIKE 'parameter%')
     */
    @Test  
    public void testLikeRight(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.likeRight("user_name","可乐");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ isNull 判断字段为 null
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_name IS NULL)
     */
    @Test  
    public void testIsNull(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.isNull("user_name");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ isNotNull 判断字段不为 null
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_name IS NOT NULL)
     */
    @Test  
    public void testIsNotNull(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.isNotNull("user_name");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ in 范围定值查询
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_age IN (?,?,?))
     */
    @Test  
    public void testIn(){
        QueryWrapper queryWrapper = new QueryWrapper();
        List queryList = new ArrayList<>();
        queryList.add(18);
        queryList.add(1);
        queryList.add(25);
        queryWrapper.in("user_age",queryList);
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ notIn
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_age IN (?,?,?))
     */
    @Test  
    public void testNotIn(){
        QueryWrapper queryWrapper = new QueryWrapper();
        List queryList = new ArrayList<>();
        queryList.add(18);
        queryList.add(1);
        queryList.add(25);
        queryWrapper.notIn("user_age",queryList);
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ inSql
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (id IN (select id from user))
     */
    @Test  
    public void testInSql(){
        QueryWrapper queryWrapper = new QueryWrapper();
        // 查询所有数据
        queryWrapper.inSql("id","select id from user");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ notInSql
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (id NOT IN (select id from user where id> 2))
     */
    @Test  
    public void testNotInSql(){
        QueryWrapper queryWrapper = new QueryWrapper();
        // 查询所有数据
        queryWrapper.notInSql("id","select id from user where id> 2");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ groupBy 分组
     _ 下面 SQL 有个问题，在 MySQL8.0 版本中，是可以执行下面 SQL 语句的，select user_name 并没有出现在 group by 语句中
     _ 实例 SQL：SELECT id,user_name,user_age FROM user GROUP BY id,user_age
     _/
    @Test  
    public void testGroupBy(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.groupBy("id","user_age");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ orderByAsc 升序
     _ 实例 SQL：SELECT id,user_name,user_age FROM user ORDER BY id ASC,user_age ASC
     */
    @Test  
    public void testOrderByAsc(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.orderByAsc("id","user_age");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ orderByDesc 降序
     _ 实例 SQL：SELECT id,user_name,user_age FROM user ORDER BY id DESC,user_age DESC
     */
    @Test  
    public void testOrderByDesc(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.orderByDesc("id","user_age");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ orderBy 指定顺序排序
     _ 实例 SQL：SELECT id,user_name,user_age FROM user ORDER BY id ASC,user_age ASC
     */
    @Test  
    public void testOrderBy(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.orderBy(true,true,"id","user_age");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ having
     _ 实例 SQL：SELECT id,user_name,user_age FROM user GROUP BY id,user_age HAVING sum(user_age)>?
     */
    @Test  
    public void testHaving(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.groupBy("id","user_age");
        queryWrapper.having("sum(user_age)>{0}","25");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ having
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (id = ? OR user_age = ?)
     */
    @Test  
    public void testOr(){
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.eq("id",1);
        queryWrapper.or();
        queryWrapper.eq("user_age",25);
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ and
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE ((id = ? AND user_age <> ?))
     */
    @Test  
    public void testAnd(){
        QueryWrapper queryWrapper = new QueryWrapper<>();
        queryWrapper.and(i->i.eq("id",1).ne("user_age",18));
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ nested
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE ((id = ? AND user_age <> ?))
     */
    @Test  
    public void testNested(){
        QueryWrapper queryWrapper = new QueryWrapper<>();
        queryWrapper.nested(i->i.eq("id",1).ne("user_age",18));
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ apply
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (user_age>?)
     */
    @Test  
    public void testApplyd(){
        QueryWrapper queryWrapper = new QueryWrapper<>();
        queryWrapper.apply("user_age>{0}","25 or 1=1");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ last
     _ 实例 SQL：SELECT id,user_name,user_age FROM user limit 1
     */
    @Test  
    public void testLast(){
        QueryWrapper queryWrapper = new QueryWrapper<>();
        queryWrapper.last("limit 1");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ exists
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (EXISTS (select id from user where user_age = 1))
     */
    @Test  
    public void testExists(){
        QueryWrapper queryWrapper = new QueryWrapper<>();
        queryWrapper.exists("select id from user where user_age = 1");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
/**
     _ notExists
     _ 实例 SQL：SELECT id,user_name,user_age FROM user WHERE (EXISTS (select id from user where user_age = 1))
     */
    @Test  
    public void testNotExists(){
        QueryWrapper queryWrapper = new QueryWrapper<>();
        queryWrapper.notExists("select id from user where user_age = 1");
        List list = userMapper.selectList(queryWrapper);
        System.out.println(list);
    }
}

4、LambdaQueryWrapper 和 LambdaUpdateWrapper（推荐）

LambdaQueryWrapper 和 LambdaUpdateWrapper 这是相对于 QueryWrapper 及 UpdateWrapper 的 Lmbda 语法实现方式。

分别通过如下两种方式获取：

// 两种方式        
LambdaQueryWrapper queryLambda = new QueryWrapper().lambda();
LambdaQueryWrapper lambdaQueryWrapper = new LambdaQueryWrapper<>();

// 两种方式
LambdaUpdateWrapper updateLambda = new UpdateWrapper().lambda();
LambdaUpdateWrapper lambdaUpdateWrapper = new LambdaUpdateWrapper();


/**
注意：获取 LambdaQueryWrapper 和 LambdaUpdateWrapper 对象时，为了使用 lambda 语法，要使用泛型。

下面我演示几个实例：
**/
/**
 _ LambdaQueryWrapper
 _ SQL 实例：SELECT id,user_name,user_age FROM user WHERE (id = ? AND user_age <> ?)
 */
@Test  
public void testLambdaQueryWrapper(){
    LambdaQueryWrapper queryLambda = new LambdaQueryWrapper<>();
    queryLambda.eq(User::getId,"1").ne(User::getUserAge,25);
    List users = userMapper.selectList(queryLambda);
    System.out.println(users);

}

/**
 _ LambdaQueryWrapper
 _ SQL 实例：UPDATE user SET user_name=? WHERE (user_name = ?)
 */
@Test  
public void testLambdaUpdateWrapper(){
    User user = new User();
    user.setUserName("LambdaUpdateWrapper");
    LambdaUpdateWrapper userLambdaUpdateWrapper = new LambdaUpdateWrapper<>();
    userLambdaUpdateWrapper.eq(User::getUserName,"IT 可乐");
    userMapper.update(user,userLambdaUpdateWrapper);

}

5、总结

对于 mybatis plus 中的四种条件构造器，我们就到此结束了，大家可以按照我的实例敲一遍代码，基本上就没啥问题了。

有没有发现使用 Lambda 语法很爽，语法简洁，另外有个优点是，使用 QueryWrapper 或者 UpdateWrapper 时，对于条件的某个列，我们是写的字符串配置，比如 QueryWrapper.eq(“id”,1); 这里的 id 是数据库表的列名，很有可能我们会写错，但是通过 lambda 的方式，LambdaQueryWrapper.eq(User::getId,1)，这样就不会有写错的可能了。所以推荐大家使用 Lambda 的方式。

至此，mybatis plus 的常规用法就全部介绍结束了，当然，事情还远没有结束，为了让大家用得更爽，后续将给大家介绍一些高阶玩法。