Can't using the `findAndModify` to update specific field.

[SittiphanSittisak]

The result always be null from this code:

  Map<String, dynamic> data = await mongodb.dbCollection.findAndModify(
    update: [
      {'field A': 'data A'},
      {'field B': 'data B'},
    ],
    query: where.id(ObjectId.parse('Object Id')),
    returnNew: true,
  );

but it works with this code. But I don't want to replace the document:

  Map<String, dynamic> data = await mongodb.dbCollection.findAndModify(
    update: {'field A': 'data A', 'field B': 'data B'},
    query: where.id(ObjectId.parse('Object Id')),
    returnNew: true,
  );

I get an error Exception: Not implemented for ModifierBuilder({$set: {field A: data A}})
When I try using modify.set like this:

  Map<String, dynamic> data = await mongodb.dbCollection.findAndModify(
    update: [
      modify.set('field A', 'data A'),
      modify.set('field B', 'data B'),
    ],
    query: where.id(ObjectId.parse('Object Id')),
    returnNew: true,
  );

What do I mistake?

[giorgiofran]

Please, give a look to the update field

[SittiphanSittisak]

Yes, I have seen this.
I tried to find an example of using an Aggregation Pipeline in dart or mongo_dart.
The search result has one example as the image below.

And I tried with code from the doc as below.

db.students.updateOne( { _id: 3 }, [ { $set: { "test3": 98, modified: "$$NOW"} } ] )

Now, I find the solution that works for mongo_dart:
first:

  Map<String, dynamic> data = await mongodb.dbCollection.findAndModify(
    update: (AggregationPipelineBuilder()
          ..addStage(SetStage({
            'field A': 'data A',
            'field B': 'data B',
          }))).build(),
    query: where.id(ObjectId.parse('Object Id')),
    returnNew: true,
  );

second:

  Map<String, dynamic> data = await mongodb.dbCollection.findAndModify(
    update: [
         {
             '\$set': {
               'field A': 'data A',
               'field B': 'data B',
             }
         }
    ],
    query: where.id(ObjectId.parse('Object Id')),
    returnNew: true,
  );