firestore 规则中是否有循环？

我想知道是否有更简单的方法来实现这个规则。刚刚开始尝试 firestore。

match /emails/{emailId} {

    allow write: if request.resource.data.attachments.size() == 0
    || request.resource.data.attachments.size() == 1 && request.resource.data.attachments[0].fileSize < 3 * 1024 * 1024 && (request.resource.data.attachments[0].filetype == 'image/png' || request.resource.data.attachments[0].filetype == 'image/jpg' || request.resource.data.attachments[0].filetype == 'application/vnd.ms-excel')
    || request.resource.data.attachments.size() == 2 && request.resource.data.attachments[0].fileSize < 3 * 1024 * 1024 && (request.resource.data.attachments[0].filetype == 'image/png' || request.resource.data.attachments[0].filetype == 'image/jpg' || request.resource.data.attachments[0].filetype == 'application/vnd.ms-excel') && request.resource.data.attachments[1].fileSize < 3 * 1024 * 1024 && (request.resource.data.attachments[1].filetype == 'image/png' || request.resource.data.attachments[1].filetype == 'image/jpg' || request.resource.data.attachments[1].filetype == 'application/vnd.ms-excel')
    || request.resource.data.attachments.size() == 3 && request.resource.data.attachments[0].fileSize < 3 * 1024 * 1024 && (request.resource.data.attachments[0].filetype == 'image/png' || request.resource.data.attachments[0].filetype == 'image/jpg' || request.resource.data.attachments[0].filetype == 'application/vnd.ms-excel') && request.resource.data.attachments[1].fileSize < 3 * 1024 * 1024 && (request.resource.data.attachments[1].filetype == 'image/png' || request.resource.data.attachments[1].filetype == 'image/jpg' || request.resource.data.attachments[1].filetype == 'application/vnd.ms-excel') && request.resource.data.attachments[2].fileSize < 3 * 1024 * 1024 && (request.resource.data.attachments[2].filetype == 'image/png' || request.resource.data.attachments[2].filetype == 'image/jpg' || request.resource.data.attachments[2].filetype == 'application/vnd.ms-excel')
    || request.resource.data.attachments.size() == 4 && request.resource.data.attachments[0].fileSize < 3 * 1024 * 1024 && (request.resource.data.attachments[0].filetype == 'image/png' || request.resource.data.attachments[0].filetype == 'image/jpg' || request.resource.data.attachments[0].filetype == 'application/vnd.ms-excel') && request.resource.data.attachments[1].fileSize < 3 * 1024 * 1024 && (request.resource.data.attachments[1].filetype == 'image/png' || request.resource.data.attachments[1].filetype == 'image/jpg' || request.resource.data.attachments[1].filetype == 'application/vnd.ms-excel') && request.resource.data.attachments[2].fileSize < 3 * 1024 * 1024 && (request.resource.data.attachments[2].filetype == 'image/png' || request.resource.data.attachments[2].filetype == 'image/jpg' || request.resource.data.attachments[2].filetype == 'application/vnd.ms-excel') && request.resource.data.attachments[3].fileSize < 3 * 1024 * 1024 && (request.resource.data.attachments[3].filetype == 'image/png' || request.resource.data.attachments[3].filetype == 'image/jpg' || request.resource.data.attachments[3].filetype == 'application/vnd.ms-excel');
}

我们不允许在规则中使用循环构造，因为我们依赖于多种优化技术，而这些技术对于更复杂的结构来说会更加困难。我们也不收取规则执行的计算时间，这意味着我们不希望它们变得太复杂并且可能被滥用。

由于规则中的重复，我强烈鼓励使用 function() 功能来简化。例如，这是

match /emails/{emailId} {
    function attachments (){
      return request.resource.data.attachments();
    }

    function attach_cnt () {
      return attachments().size();
    }

    function valid_size(attach) {
      return attachments()[attach].fileSize < 3 * 1024 * 1024;
    }

    function valid_type(attach) {
      return (attachments()[attach].filetype == 'image/png' 
         || attachments()[attach].filetype == 'image/jpg'
         || attachments()[attach].filetype == 'application/vnd.ms-excel');
    }

    allow write: (attach_cnt() < 1 || (valid_size(0) && valid_type(0)))
    && (attach_cnt() < 2 || (valid_size(1) && valid_type(1)))
    && (attach_cnt() < 3 || (valid_size(2) && valid_type(2)))
    && (attach_cnt() < 4 || (valid_size(3) && valid_type(3)))
}

这是我如何简化它的（值得仔细检查，因为我可能输入错误）。

1. 我做了一个函数attachments对于正在访问的请求数据，因为它使用了一堆 - 这使得浏览规则变得很容易。
2. 我做了一个函数attach_cnt因为已经检查了很多附件的数量。
3. 现在我看到每个附件都有文件大小限制，所以我做了一个函数valid_size对于该测试，使用参数attach我可以通过它。
4. 接下来是功能valid_type其工作方式相同，但进行了检查以确保它是有效的类型。
5. 现在很明显，对于具有 2-4 个项目等的请求，对附件 0 执行相同的检查。重新排序一些逻辑使您只需检查每个附件一次。