当本地更改时，onSnapshot fromCache始终为false [英] onSnapshot fromCache always false when change is local

问题描述

根据说明此处我希望在与侦听器相同的客户端中修改正在侦听的文档时，为 true .

According to the description here I'd expect snapshot.metadata.fromCache to be true when the document being listened to is modified in the same client as the listener, e.g.

1. 本地 .update(...)立即触发 onSnapshot 处理程序(并通过将 fromCache 设置为 true )
2. 数据已发送到数据库
3. firebase客户端收到返回消息，但不执行任何操作(不会触发 onSnapshot )，因为服务器数据与缓存一致.

1. The local .update(...) immediately triggers the onSnapshot handler (and is handed a snapshot with fromCache set to true)
2. The data is sent to the db
3. The firebase client receives the return message and does nothing (does not trigger a onSnapshot) because the server data agrees with the cache.

Ergo， fromCache 在本地快照触发onSnapshot时应始终为 true .

Ergo, fromCache should always be true when onSnapshot is trigged by a local change.

但是，仅在前两到三个onSnapshot响应中出现这种情况，此后 fromCache 似乎始终是 false .

However, this only appears to be the case on the first two to three onSnapshot responses, after-which fromCache appears to always be false.

示例测试:

// ... firestore init w/ a test project and with persistence enabled. 

const db = firebase.firestore();
db.settings({
    ignoreUndefinedProperties:true
})

// Where "_test" is an empty collection with full allowance for read/write
await db.collection("_test").doc("deleteme").set({}); 

let doc = db.collection("_test").doc("deleteme") 

// ?! Expect this to be true but after the first one or two occurrences it is always false.
doc.onSnapshot(s=>{console.log("test snapshot change from cache? ",s.metadata.fromCache)}) 

let x = 0;      
let poke = async ()=>{
  doc.update({
    n:Math.random()
  })
  await sleep(3000); // generic custom delay 
  window.requestAnimationFrame(poke)
};
window.requestAnimationFrame(poke);

编辑:此处的问题是由于与其他问题类似的缺少知识造成的:

Edit: The question here is due to similarly missing knowledge as in this other question: Is Firestore onSnapshot update event due to local client Set?

推荐答案

因此，当onSnapshot被本地更改触发时，fromCache应该始终为true.

Ergo, fromCache should always be true when onSnapshot is trigged by a local change.

我不认为它是这样定义的；客户端是否知道其本地快照是否与服务器有关是更多.

I don't think that is how it is defined; it is more whether the client knows if its local snapshot is up-to-date with the server.

您可能会将 fromCache 与 hasPendingWrites 混淆. fromCache 名称确实令人困惑.我理解 fromCache 为可能尚未包含来自服务器的所有数据"，而 isPending 为可能包含服务器尚不知道的数据".

You maybe confusing fromCache with hasPendingWrites. The fromCache name is indeed confusing. I understand fromCache as "may not contain all data from the server yet", while the isPending is "may contain data that the server doesn't know about yet".

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