7、Mybatis-Plus condition的使用

文章目录

1、condition

• 在真正开发的过程中，组装条件是常见的功能，而这些条件数据来源于用户输入，是可选的，因此我们在组装这些条件时，必须先判断用户是否选择了这些条件，若选择则需要组装该条件，若没有选择则一定不能组装，以免影响SQL执行的结果

2、使用带condition参数的重载方法构建查

@Test
    public void test10(){
        /**
         *StringUtils.isNotBlank()判断某字符串是否不为空且长度不为0且不由空白符(whitespace) 构成
         * 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 <= ?)
         */
        String username = "a";
        Integer ageBegin = null;
        Integer ageEnd = 30;
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.like(StringUtils.isNotBlank(username),"user_name",username)
                .ge(ageBegin != null,"age",ageBegin)
                .le(ageEnd != null,"age",ageEnd);
        List<User> list = userMapper.selectList(queryWrapper);
        list.forEach(System.out::println);
    }

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3、LambdaQueryWrapper

@Test
    public void test11(){
        /**
         *   防止字段写错
         *  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 <= ?)
         */
        String username = "a";
        Integer ageBegin = null;
        Integer ageEnd = 30;
        LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();
        queryWrapper.like(StringUtils.isNotBlank(username),User::getName,username)
                .ge(ageBegin != null,User::getAge,ageBegin)
                .le(ageEnd != null,User::getAge,ageEnd);
        List<User> users = userMapper.selectList(queryWrapper);
        users.forEach(System.out::println);
    }

---

@Test
    public void test12(){

        /**
         * 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))
         */
        LambdaUpdateWrapper<User> updateWrapper = new LambdaUpdateWrapper<>();
        updateWrapper.like(User::getName,"a")
                .and(i-> i.gt(User::getAge,20).or().isNull(User::getEmail));
        updateWrapper.set(User::getName,"唐僧").set(User::getEmail,"[e-mail]");
        int rs = userMapper.update(null,updateWrapper);
        System.out.println(rs);
    }