Firestore offline persistence flutter docId

Question

I have an app that uses firestore, when the user clicks a button I add a document, in which after its creation, I also add its documentId in a field , which is an alphanumeric string generated by firestore. My problem is that if a user clicks the button without internet, then closes the app and opens it with an internet connection the document gets created, but of course its Id inside it is null, since the programm stopped executing. Is there a way I can persist that?

for example

DocumentReference documentReference =
      await FirebaseFirestore.instance.collection('sth').add(map); //map has a 'docId' key

 await FirebaseFirestore.instance
  .collection('sth')
  .doc('${documentReference.id}')
  .update({'docId': documentReference.id});

The update one does not have offline persistence, is there any way around it?

Try using set instead of update

Dmytro Rostopira
– Dmytro Rostopira

2021-01-21 13:49:05 +00:00
Commented Jan 21, 2021 at 13:49 — Dmytro Rostopira
– Dmytro Rostopira, Commented Jan 21, 2021 at 13:49
It doesn't work with set

user14624595
– user14624595

2021-01-22 07:39:16 +00:00
Commented Jan 22, 2021 at 7:39 — user14624595
– user14624595, Commented Jan 22, 2021 at 7:39

Frank van Puffelen · Accepted Answer · 2021-01-28 15:28:03Z

0

As Dima commented, you can solve this by first generating the ID, and only then writing the document with both the data and its ID.

To generate a document ID without writing to it, you can call doc() on the CollectionReference without an argument.

DocumentReference documentReference =
     FirebaseFirestore.instance.collection('sth').doc();

map["docId"] = documentReference.id;

FirebaseFirestore.instance
  .collection('sth')
  .doc('${documentReference.id}')
  .set(map);

Now the first line is a pure client-side operation, without any data being written to the database yet - so you end up with a single, atomic write/set().

edited Jan 28, 2021 at 15:28

answered Jan 21, 2021 at 14:44

Frank van Puffelen

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6 Comments

user14624595 Over a year ago

We basically do the same thing, you create a black document, while I write a new one. I believe the problem is that since documentReference.id is a runtime variable, when I start the app again and it makes the request automatically the value is null in that point of time. Is there any way around this?

user14624595 Over a year ago

The answer lies in the middle actually. I should create a document reference but without an await method and then set the document with that id again without await, since I need every other function just like above to cache. Then when the user finds internet again the functions are being called. The main problem was in the use of await.

Frank van Puffelen Over a year ago

The await in my first snippet is indeed not needed; I removed it. The more important thing about my answer is that a doc() call without any arguments does not actually create a document in the database, but merely a reference. Only the call to set() creates the document.

Frank van Puffelen Over a year ago

@user14624595 Did you make any progress here?

Frank van Puffelen Over a year ago

Done. Good to hear you got it working. 👍

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