mybatis plus的常规用法

上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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< Integer > queryList = new ArrayList<  >();
        queryList.add(18);
        queryList.add(1);
        queryList.add(25);
        queryWrapper.in("user_age",queryList);
        List< User > 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< Integer > queryList = new ArrayList<  >();
        queryList.add(18);
        queryList.add(1);
        queryList.add(25);
        queryWrapper.notIn("user_age",queryList);
        List< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > 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< User > queryWrapper = new QueryWrapper<  >();
        queryWrapper.and(i- >i.eq("id",1).ne("user_age",18));
        List< User > 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< User > queryWrapper = new QueryWrapper<  >();
        queryWrapper.nested(i- >i.eq("id",1).ne("user_age",18));
        List< User > 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< User > queryWrapper = new QueryWrapper<  >();
        queryWrapper.apply("user_age >{0}","25 or 1=1");
        List< User > 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< User > queryWrapper = new QueryWrapper<  >();
        queryWrapper.last("limit 1 ");
        List< User > 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< User > queryWrapper = new QueryWrapper<  >();
        queryWrapper.exists("select id from user where user_age = 1");
        List< User > 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< User > queryWrapper = new QueryWrapper<  >();
        queryWrapper.notExists("select id from user where user_age = 1");
        List< User > 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< User > queryLambda = new LambdaQueryWrapper<  >();
    queryLambda.eq(User::getId,"1").ne(User::getUserAge,25);
    List< User > 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< User > 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 Lamba 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，为了让大家用的更爽，后续将给大家介绍一些高阶玩法。