How do you listen for changes in a Firestore collection if a document is added or deleted that matches a query? This is for an iOS app in Objective-C.
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1 Answer
You can use addSnapshotListener on your Query:
[[[self.db collectionWithPath:@"cities"] queryWhereField:@"state" isEqualTo:@"CA"] addSnapshotListener:^(FIRQuerySnapshot *snapshot, NSError *error) { if (snapshot == nil) { NSLog(@"Error fetching documents: %@", error); return; } NSMutableArray *cities = [NSMutableArray array]; for (FIRDocumentSnapshot *document in snapshot.documents) { [cities addObject:document.data[@"name"]]; } NSLog(@"Current cities in CA: %@", cities); }]; This listener will to documents where state field is CA. You can read more about this in the documentation