How to listen only changed documents

Question

I have used below code to listen Firestore collection change,

firestoreInstance
    .collection('Countries')
    .snapshots()
    .listen((result) async {

});

When a document change in Countries collection on Firestore. I expect result value should have only changed document. But result value has all the collection data.

How to get only changed document in result value.

Im using Flutter Firestore.

What you're asking for is not a feature of the Firestore API. See my answer here: https://stackoverflow.com/questions/66610587/listen-only-to-changes-in-document-instead-of-all-the-time and Doug's here: https://stackoverflow.com/questions/62314708/firestore-get-only-the-changed-documents-in-a-large-synced-collection — Frank van Puffelen, Jun 02 '23 at 00:48

Rohan Jariwala · Answer 1 · 2023-06-01T19:25:56.347

Here is your potential answer There are 3 types of changes can happen for document

New Doc added
Doc updated
Doc deleted

Here is example how to handle all of them :

firestoreInstance
    .collection('Countries')
    .snapshots()
    .listen((QuerySnapshot snapshot) {
  snapshot.docChanges.forEach((DocumentChange change) {
    if (change.type == DocumentChangeType.added) {
      // Handle added document
      print("Added document: ${change.doc.data()}");
    } else if (change.type == DocumentChangeType.modified) {
      // Handle modified document
      print("Modified document: ${change.doc.data()}");
    } else if (change.type == DocumentChangeType.removed) {
      // Handle removed document
      print("Removed document: ${change.doc.data()}");
    }
  });
});

Another way is if you want to check for updated docs only

firestoreInstance
    .collection('Countries')
    .snapshots()
    .listen((QuerySnapshot snapshot) {
  var modifiedDocuments = snapshot.docChanges
      .where((change) => change.type == DocumentChangeType.modified)
      .map((change) => change.doc)
      .toList();

  // Process the modified documents
  modifiedDocuments.forEach((modifiedDocument) {
    // Do something with the modified document
    print('Modified document: ${modifiedDocument.data()}');
  });
});

Here is the reference for that

https://firebase.google.com/docs/reference/android/com/google/firebase/firestore/DocumentChange

I donot want to iterate each snapshot and check document status. I want to get only updated doc snapshot. But result value has all the collection data. — praveenb, Jun 01 '23 at 18:37
Sorry for that but Firebase does not provide a direct mechanism to listen for only updated documents. As there can be multiple updated document at once. — Rohan Jariwala, Jun 01 '23 at 19:21
I've updated my answer with another option if you want to use that one — Rohan Jariwala, Jun 01 '23 at 19:26

score 1 · Answer 2 · answered Jun 01 '23 at 17:47

For Flutter/Dart Firestore, you can know only changed document. Here's an example in Flutter/Dart that demonstrates how to filter out only the changed documents.

  firestoreInstance
        .collection('Countries')
        .snapshots()
        .listen((event) {
      for (var change in event.docChanges) {
        switch (change.type) {
          case DocumentChangeType.added:
            print("New Countries: ${change.doc.data()}");
            break;
          case DocumentChangeType.modified:
            print("Modified Countries: ${change.doc.data()}");
            break;
          case DocumentChangeType.removed:
            print("Removed Countries: ${change.doc.data()}");
            break;
        }
      }
    });

Here is official documentation link https://firebase.google.com/docs/firestore/query-data/listen#view_changes_between_snapshots

How to listen only changed documents

2 Answers2