Cloud Firestore规定正确的语法 [英] Cloud Firestore rules proper syntax

问题描述

我需要为Cloud Firestore编写规则.

I need to write rules for Cloud Firestore.

我希望我的规则允许在集合中创建新文档:

I want my rules to allow the creation of a new document in a collection:

newDoc(field1="value-1", field2="value-2", field3="other-miscellaneous-values")

仅当集合中不存在具有以下条件的其他文档时:

only if no other document already exists in the collection with:

(field1 == "value-1") and (field2 == "value-2")

尽管这不是很复杂，但似乎仍然太复杂了，以至于找不到我在网上搜索的任何教程中的例子.

Though this is not very complicated, it seems still too complex to be found as an example in any tutorial that I found searching the net.

此外，如果用户愿意，可以自由列出和阅读馆藏中的所有文档.

Beside, the user should be free to list and read all the documents in the collection if she/he wishes.

这是我尝试过的方法，但是不起作用:

Here is what I have tried, but it does not work:

service cloud.firestore {
  function alreadyExists(document) {
              return exists((resource.data.field1==request.resource.data.field1)&&
                           (resource.data.field2==request.resource.data.field2))
  }

  match /databases/{database}/documents {
    match /My_Collection/{anything=**} {
      allow read;
      allow write: if !(alreadyExists(request.resource.data));
    }
  }
}

我希望有人能给我一些建议，以使其正常工作.

I hope someone can give me some advice to get it working.

推荐答案

安全规则只能检查特定路径下的文档是否存在(使用exists).无法检查规则中是否存在具有特定值的文档.

Security rules can only check if a document at a certain path exists (with exists). There is no way to check if a document with a certain value exists in rules.

针对您的用例，我的典型解决方案是将要唯一的字段组合用作文档的ID.根据定义，由于文档ID在给定的集合中是唯一的，因此可以确保您的键组合在同一集合中是唯一的.

My typical solution for your use-case would be to use the combination of fields that you want to be unique as the ID of the document. Since document IDs are by definition unique in a given collection, that ensures that your combination of keys is unique in that same collection.

如果您已经拥有无法更改的ID策略，请考虑添加一个包含唯一组合的辅助集合，如我的答案所示:

If you already have an ID strategy that you can't change, consider adding a secondary collection to contain the unique combinations, as shown in my answer here: Prevent duplicate entries in Firestore rules not working.

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