将数组大小限制为最多 N 个索引(安全规则) [英] Restrict an array size up to N indices (Security Rules)

问题描述

考虑以下最大数组大小:

Consider the following maximum array size:

现在假设用户执行 push() childByAutoId.我期望发生的是

Now let's say a user performs a push() childByAutoId. What I expect to happen is

if (arraySize > arraySizeLimit) {
// Delete first Index
}

我对 Firebase 安全规则还很陌生.我做了一些阅读，但仍在为此苦苦挣扎.我为没有任何尝试"而道歉要呈现的代码.

I am fairly new to firebase security rules. I did some reading but still struggling with this. I apologise for not having any "attempt" code to present.

推荐答案

安全规则无法像这样检查列表的大小.

There's no way for security rules to check the size of a list like that.

我所知道的主要选项是:

Th main options that I know of, are:

• Kato 对这个问题的古老回答，它使用已知的节点名称来施加限制:限制可以写入路径的记录数(在安全规则中引用其他路径)
• 这个扩展或云函数，将子节点的数量减少到最大配置/em> 写操作超出了这个数字.
• 通过应用调用的单个云函数执行写入.在 Cloud Functions 中，您将读取整个消息节点并根据需要截断它.

• Kato's age-old answer to this question, which uses known node names to impose a limit: Limit number of records that can be written to a path (reference other paths in security rules)
• This extension or Cloud Function that reduces the number of child nodes to the maximum configured after a write operation goes beyond that number.
• Perform the write through a single Cloud Function, which the app calls. In the Cloud Function you'd then read the entire messages node and truncate it as needed.

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