Question 180228 in Flutter Question posted in
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Flutter – How to listen only changed documents

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.

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2

Answers


  1. 0

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

    1. New Doc added
    2. Doc updated
    3. 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

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  2. 0

    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

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