6、Mybatis-Plus wrapper的使用

1、wapper的介绍

 

 介绍：
Wrapper ： 条件构造抽象类，最顶端父类
AbstractWrapper ： 用于查询条件封装，生成 sql 的 where 条件
QueryWrapper ： 查询条件封装
UpdateWrapper ： Update 条件封装
AbstractLambdaWrapper ： 使用Lambda 语法
LambdaQueryWrapper ：用于Lambda语法使用的查询Wrapper
LambdaUpdateWrapper ： Lambda 更新封装Wrapper

 

2、QueryWrapper（组装查询条件）

    //条件构造器
    @Test
    public void test01(){
        /**
         * 查询用户名包含a，年龄在20到30之间，并且邮箱不为null的用户信息
         *
         * SELECT uid AS id,user_name AS name,age,email,is_deleted FROM t_user
         * WHERE is_deleted=0 AND
         * (user_name LIKE ? AND age BETWEEN ? AND ? AND email IS NOT NULL)
         */
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.like("user_name","三")
                    .between("age",20,25)
                    .isNotNull("email");
        List<User> list = userMapper.selectList(queryWrapper);
        list.forEach(System.out::println);
    }

 

3、QueryWrapper（组装排序条件）

    @Test
    public void test02(){
        /**
         * //按年龄降序查询用户，如果年龄相同则按id升序排列
         * //SELECT id,username AS name,age,email,is_deleted FROM t_user WHERE is_deleted=0 ORDER BY age DESC,id ASC
         */
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.orderByDesc("age")
                .orderByAsc("id");
        List<User> users = userMapper.selectList(queryWrapper);
        users.forEach(System.out::println);

    }

 

4、QueryWrapper（组装删除条件）

   @Test
    public void test03(){
        /**
         * 删除email为空的用户
         *  UPDATE t_user SET is_deleted=1 WHERE is_deleted=0 AND (email IS NULL)
         */
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.isNull("email");
        int rs = userMapper.delete(queryWrapper);
        System.out.println(rs);
    }

 

5、QueryWrapper（信息的修改）

@Test
    public void test04(){
        /**使用queryWrapper实现用户信息的修改
         * 将（年龄大于20并且用户名中包含有a）或邮箱为null的用户信息修改
         * UPDATE t_user SET user_name=?, age=? WHERE is_deleted=0 AND (age > ? AND user_name LIKE ? OR email IS NULL)
         */
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.gt("age",20)
                .like("user_name","a")
                .or()
                .isNull("email");
        User user = new User();
        user.setName("孙悟空");
        user.setAge(32);
        int rs = userMapper.update(user,queryWrapper);
        System.out.println(rs);
    }

 

6、QueryWrapper（条件的优先级）

  @Test
    public void test05(){
        /**
         * 条件的优先级
         * 将用户名中包含有a并且（年龄大于20或邮箱为null）的用户信息修改
         * lambda中的条件优先执行
         * UPDATE t_user SET user_name=?, age=?, email=? WHERE is_deleted=0 AND (user_name LIKE ? AND (age > ? OR email IS NULL))
         */
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.like("user_name","a")
                .and(i->i.gt("age",20).or().isNull("email"));
        User user = new User();
        user.setName("猪八戒");
        user.setAge(32);
        user.setEmail("zbj@qq.com");
        int rs = userMapper.update(user,queryWrapper);
        System.out.println(rs);
    }

 

7、QueryWrapper（组装select子句）

  @Test
    public void test06(){

        /**
         * 查询用户信息的username、age和email字段
         * SELECT user_name,age,email FROM t_user WHERE is_deleted=0
         */
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.select("user_name","age","email");
       List<Map<String,Object>> maps =  userMapper.selectMaps(queryWrapper);
       maps.forEach(System.out::println);
    }

 

8、QueryWrapper（实现子查询）

    @Test
    public void test07(){
        /**
         *查询uid小于等于100的用户信息
         * SELECT uid AS id,user_name AS name,age,email,is_deleted FROM t_user WHERE is_deleted=0 AND (uid IN (select uid from t_user where uid <= 100))
         */
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.inSql("uid","select uid from t_user where uid <= 100");
        List<User> list = userMapper.selectList(queryWrapper);
        list.forEach(System.out::println);

    }

 

8、QueryWrapper（UpdateWrapper）

    @Test
    public void test08(){

        /**
         * 将用户名中包含有a并且（年龄大于20或邮箱为null）的用户信息修改
         * UPDATE t_user SET user_name=?,email=? WHERE is_deleted=0 AND (user_name LIKE ? AND (age > ? OR email IS NULL))
         */
        UpdateWrapper<User> updateWrapper = new UpdateWrapper<>();
        updateWrapper.like("user_name","a")
                .and(i-> i.gt("age",20).or().isNull("email"));
        updateWrapper.set("user_name","唐僧").set("email","tangseng@qq.com");
        int rs = userMapper.update(null,updateWrapper);
        System.out.println(rs);
    }