Flutter & Firebase: Remove Item(Map) from Array in firebase

Question

I'm currently struggling to remove a map item from a list in firebase. E.g. I want to remove item "0" from the list (completely).

I add the single array items in another place via FieldValue.arrayUnion with the updateData Method. This works perfectly fine. In another place in my I then want to have the possibility to remove the item from a list. I load the data via StreamBuilder and display ListTiles via ListView.builder. Now there I tried to replace arrayUnion by arrayRemove, but it doesn't work and I can't figure out why. Here's my code:

onPressed: () async {
  try {
    await Firestore.instance
        .collection('users')
        .document(futSnap.data.uid)
        .collection('trainings')
        .document(widget.trainingID)
        .updateData(
      {
        'trainingTitle': widget.trainingTitle,
        'trainingID': widget.trainingID,
        'trainingDate': widget.trainingDate,
        'category': widget.trainingCategory,
        'trainingExercises':
            FieldValue.arrayRemove(
          [
            {
              'title': trainingExercises[i]
                  ['title'],
              'description':
                  trainingExercises[i]
                      ['description'],
              'imageURL': trainingExercises[i]
                  ['imageUrl'],
              'repetitions':
                  trainingExercises[i]
                      ['repetitions'],
            },
          ],
        )
      },
    );
  } catch (e) {
    print(e);
  }
},

I don't receive any error or something.. Still a beginner to flutter and programming, so help would be highly appreciated :)

Answer 1

Thanks for your replies, in trying further, it seems that this actually works now:

onPressed: () async {
                              try {
                                await Firestore.instance
                                    .collection('users')
                                    .document(futSnap.data.uid)
                                    .collection('trainings')
                                    .document(widget.trainingID)
                                    .updateData(
                                  {
                                    'trainingExercises':
                                        FieldValue.arrayRemove(
                                      [trainingExercises[i]],
                                    )
                                  },
                                );
                              } catch (e) {
                                print(e);
                              }
                            },

But to be fair I don't understand completely why, because my understanding was as well as yours, that the information has to match the whole map..? I'm happy that it works, but it would be awesome to understand why :D

Answer 2

List<ExpenseData> deleteExpenseData = [];
deleteExpenseData.add(spendingDetailMapList[documentIndex][documentId[documentIndex]][spending]);
expenseCR.doc(documentId[documentIndex]).update({"spending": FieldValue.arrayRemove([deleteExpenseData[0].toJson()],)});

I did this and It works.