Mybatis-plus--QueryWrapper

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基本

条件构造器，调用方法之后，传入参数，会根据方法和参数生成SQL语句，并执行，返回结果

用的时候，引入依赖，配置yml文件，编写一个mapper接口，只需继承BaseMapper，基本的单表查询都封装好了。

Mybatis-plus比mybatis方便，但是它降低了代码的 可复用性，也不利于维护，所以除了单表查询，基本不用它。

函数说明例子
eq等于(=)queryWrapper.eq(“user_name”, “张三”); //user_name=“张三”
ne不等于(<>)queryWrapper.ne(“user_name”, “张三”); //user_name<>“张三”
gt大于(>)queryWrapper.gt(“level”, 1); //level>1
ge大于等于(>=)queryWrapper.ge(“level”, 1); //level>=1
lt小于(<)queryWrapper.lt(“level”, 1); //level<1
le小于等于(<=)queryWrapper.le(“level”, 1); //level<=1
between值1和值2之间queryWrapper.between(“level”, 1,10); //level>=1 and level <=10
notBetween不在值1和值2之间queryWrapper.notBetween(“level”, 1,10);//level<1 or level >10
like模糊匹配 like %值%queryWrapper.like(“user_name”, “张三”); //user_name like “%张三%”
not like不模糊匹配 not like %值%queryWrapper.notLike(“user_name”, “张三”); //user_name not like “%张三%”
likeLeft左模糊匹配 like %值queryWrapper.likeLeft(“user_name”, “张三”); //user_name like “%张三”
likeRight右模糊匹配 like 值%queryWrapper.likeRight(“user_name”, “张三”); //user_name like “张三%”
isNull字段 为空queryWrapper.isNull(“user_name”);//user_name is null
isNotNull字段 不为空queryWrapper.isNotNull(“user_name”);//user_name is not null
in字段 in (v0，v1，…)queryWrapper.in(“user_name”, {“张三”,“李四”,“王五”}); // user_name in （“张三”,“李四”,“王五”）
notIn字段 not in (v0，vl，…)queryWrapper.notIn(“user_name”, {“张三”,“李四”,“王五”}); // user_name not in （“张三”,“李四”,“王五”）
inSql字段 in ( sql语句)queryWrapper.in(“user_name”, (select name from student where age< 23)); // user_name in (select name from student where age< 23)
notInSql字段 not in ( sql语句)queryWrapper.notIn(“user_name”, (select name from student where age< 23)); // user_name not in (select name from student where age< 23)
groupBy分组:GROUP BY 字段queryWrapper.groupBy(“user_name”);//group by user_name
orderByAsc排序:ORDER BY 字段 ASCqueryWrapper.orderByAsc(“createTime”);//order by createTime asc
orderByDesc排序:ORDER BY 字段 DESCqueryWrapper.orderByDesc(“createTime”);//order by createTime desc
orderBy排序:ORDER BY 字段queryWrapper.orderBy(true, true, “createTime”);//order by createTime asc
or拼接 OR说明:主动调用or表示紧接着下一个方法不是用and连接!(不调用or则默认为使用and连接);queryWrapper.eq(“id”, “1”).or().eq(“user_name”, “张三”); //id = 1 or name =‘张三’
and拼接 ANDqueryWrapper.eq(“id”, “1”).and(i->i.eq(“user_name”, “张三”)); //id = 1 and name =‘张三’
apply拼接 sql说明: 该方法可用于数据库函数动态入参的params;queryWrapper.eq(“id”, user.getId()).apply(“date_format(‘createTime’,‘%Y-%m-%d’) = {0}”,“2023-07-25”);//date_format(‘createTime’,'%Y-%m-%d) =‘2023-07-25’")
last无视优化规则直接拼接到 sql 的最后说明:只能调用一次,多次调用以最后一次为准 有sq1注入的风险,请谨慎使用queryWrapper.last(" limit 1");// limit 1
exists拼接 EXISTS(sql语句)queryWrapper.exists(“SELECT id FROM Student WHERE User.id = Student.userId”);// exists (“SELECT id FROM Student WHERE User.id = Student.userId”)
notExists拼接 NOT EXISTS (sg1语句)queryWrapper.notExists(“SELECT id FROM Student WHERE User.id = Student.userId”);// not exists (“SELECT id FROM Student WHERE User.id = Student.userId”)
nested正常嵌套不带 AND或者 ORqueryWrapper.nested(i->i.eq(“id”,“1”).eq(“user_name”,“张三”));// id = 1 and user_name=“张三”
havinghaving ( sql语句)queryWrapper.having(“sum(age) > {0}”,10);//having sum(age) > 10;

例子

1.查询用户名包含a，年龄在20到30直接，邮箱信息不为空的信息

    @DisplayName("条件构造器组装查询条件")
    @Test
    public void test01(){
// SELECT id,name,age,email,is_deleted FROM user WHERE is_deleted=0 AND (name LIKE ? AND age BETWEEN ? AND ? AND email IS NOT NULL)
        QueryWrapper<User> wrapper=new QueryWrapper<>();
        wrapper.like("name","a").
                between("age",20,30).
                isNotNull("email");
        List<User> list = userMapper.selectList(wrapper);
        list.forEach(System.out::println);
    }

2.查询用户信息，按照年龄降序排序，若年龄相同，则按id升序排序

 @DisplayName("条件构造器组装排序条件")
    @Test
    public void test02(){
//SELECT id,name,age,email,is_deleted FROM user WHERE is_deleted=0 ORDER BY age DESC,id ASC
        QueryWrapper<User> queryWrapper=new QueryWrapper<>();
        queryWrapper.orderByDesc("age").orderByAsc("id");
        List<User> list = userMapper.selectList(queryWrapper);
        list.forEach(System.out::println);
    }

3.删除邮箱地址为null的数据

 @DisplayName("条件构造器删除功能")
    @Test
    public void test03(){
//UPDATE user SET is_deleted=1 WHERE is_deleted=0 AND (email IS NULL)
        QueryWrapper<User> queryWrapper=new QueryWrapper<>();
        queryWrapper.isNull("email");
        int delete = userMapper.delete(queryWrapper);
        System.out.println(delete);
    }
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