写入 Firebase Cloud Firestore

Question

Is writing to firebase cloud firestore asynchronous in javascript? And if it is, what is a way to deal with it?

My program is supposed to update a value into the database, and then pull that value out soon after, to do something with it.

Most of the times, the correct value comes out, however, sometimes the previous value is outputted, but when the page is refreshed and the same value is read from the database again, the correct value gets outputted.

So, I am assuming the issue must be that writing to the database is asynchronous, just like reading a database is.

".then" didn't seem to work.

Here is a simplified version of my code:

function updateDB{
 db.collection("rooms").doc("roomsDoc").update({
   roomTime: timeInput  //timeInput is a variable defined (not shown in code here)              
  }).then
  {
   readDB();
  }
}

function readDB(){
   db.collection("rooms").doc("roomsDoc").get().then(function(doc) {
     console.log(doc.data().roomTime);
   });
}

The console.log is what outputs the wrong value sometimes.

Answer 1

yes it is asynchronous.

a good way to handle the problem you are having is to async/await .

first, you need to make the function you are doing this in an async function

then do something like this

async function FunctionName(){
    // do some initial stuff
    await write to the database
    // do some intermediate stuff
    await read from the database
}

Answer 2

All JavaScript client/browser APIs that work with files and networks are asynchronous - that is the nature of JavaScript.

then() does, in fact, work on the promises returned by Firestore's APIs (and all promises, for that matter). There are lots of examples of this in thedocumentation .

Without seeing your code, we don't know what you might be doing wrong.

Answer 3

Yes, it is asynchronous.

You should check the official documentation regarding this topic, it was very useful to me when trying to fetch data from the database/API:

Firebase Cloud Firestore

First you have to initialize your document ref and fetch data with get() async function and wait for the response using either then() or async/await method.

Hope this helps!

Answer 4

I think you made a typo here:

.then
  {
   readDB();
  }

in this way, you are not really waiting for the completion of the first operation. To get what you want you need to write:

.then(() => readDB())