Feature/support more aggregate queries

[ming-chu]

Hi @atn832,

This PR is going to support aggregate queries on getSum and getAverage for cloud_firestore: ^4.14.0.
Please feel free to comment, any code refactors or edits are welcome.

Please let me know if any test cases are missed, hope this PR can help.

#289

[atn832]

I tried using Dart 3.0's new Switch expressions but sadly it didn't work because the value wasn't a type 😞 .

final fieldType = switch (type) {
  AggregateType.sum => platform_interface.sum,
  AggregateType.average => platform_interface.average,
  AggregateType.count => platform_interface.count,
  _ => throw UnimplementedError('Unknown AggregateType: $type')
};
final nonNullFields = fields.whereNotNull();
// compiler says: The name 'fieldType' isn't a type, so it can't be used as a type argument.
// Try correcting the name to an existing type, or defining a type named 'fieldType'.
return nonNullFields.whereType<fieldType>();

https://dart.dev/language/branches#switch-expressions

[ming-chu]

I did a little search about it, seems we cannot pass the value as Generic Type
https://stackoverflow.com/questions/66021661/how-can-i-cast-a-variable-to-generic-type-in-dart

[ming-chu]

btw, maybe we could use where instead:

return nonNullFields.where((e) => e.runtimeType == fieldType);

[ming-chu]

I tried using Dart 3.0's new Switch expressions but sadly it didn't work because the value wasn't a type 😞 .

final fieldType = switch (type) {
  AggregateType.sum => platform_interface.sum,
  AggregateType.average => platform_interface.average,
  AggregateType.count => platform_interface.count,
  _ => throw UnimplementedError('Unknown AggregateType: $type')
};
final nonNullFields = fields.whereNotNull();
// compiler says: The name 'fieldType' isn't a type, so it can't be used as a type argument.
// Try correcting the name to an existing type, or defining a type named 'fieldType'.
return nonNullFields.whereType<fieldType>();

https://dart.dev/language/branches#switch-expressions

That's good to simplify the code which makes it easier to read. Nice!

[atn832]

btw, maybe we could use where instead:

return nonNullFields.where((e) => e.runtimeType == fieldType);

Oh! Good idea

[atn832]

This won't work for converted queries.

In fake_cloud_firestore_test.dart, I added the 'crew' integer field:

class Movie {
  late String title;
  late int crew;
}

final from =
    (DocumentSnapshot<Map<String, dynamic>> snapshot, _) => snapshot.exists
        ? (Movie()
          ..title = snapshot['title']
          ..crew = snapshot['crew'])
        : null;
final to = (Movie? movie, _) => movie == null
    ? <String, Object?>{}
    : {
        'title': movie.title,
        'crew': movie.crew,
      };

Then in mock_query_test.dart, I added this test case:

test('with Converters', () async {
  final firestore = FakeFirebaseFirestore();
  final movies = firestore
      .collection('movies')
      .withConverter(fromFirestore: from, toFirestore: to);
  await movies.add(Movie()
    ..title = 'Best Movie'
    ..crew = 30);
  await movies.add(Movie()
    ..title = 'Worst Movie'
    ..crew = 20);
  final snapshot =
      await movies.aggregate(sum('crew'), average('crew')).get();
  expect(snapshot.count, 2);
  expect(snapshot.getSum('crew'), 50);
  expect(snapshot.getAverage('crew'), 25);
});

I got:

type 'Movie' is not a subtype of type 'Map<String, dynamic>' in type cast
package:fake_cloud_firestore/src/fake_aggregate_query.dart 34:56   FakeAggregateQuery._getAggregateQuerySnapshotPlatform.<fn>
dart:_internal                                                     ListIterator.moveNext
package:fake_cloud_firestore/src/fake_aggregate_query.dart 107:27  FakeAggregateQuery.buildAggregateQueryResponseList
package:fake_cloud_firestore/src/fake_aggregate_query.dart 37:12   FakeAggregateQuery._getAggregateQuerySnapshotPlatform
package:fake_cloud_firestore/src/fake_aggregate_query.dart 21:22   FakeAggregateQuery.get

I'll merge this because it works well for non-converted queries. We can tackle converted queries in a separate PR.

[ming-chu]

@atn832 I just made another PR to fix this problem, but I am not sure that's a good way to fix it. Please advise.
Thank you very much!😃
#291

[atn832]

I was going to suggest using setUpAll, but then I saw your last test case, which uses different data.

late FakeFirebaseFirestore firestore;
late CollectionReference collection;

setUpAll(() async {
  firestore = FakeFirebaseFirestore();
  collection = firestore.collection('firestore-example-app');

  await collection.add({'name': 'Banana', 'likes': 1, 'dislikes': 4});
  await collection.add({'name': 'Avocado', 'likes': 2, 'dislikes': 5});
  await collection.add({'name': 'Mango', 'likes': 3, 'dislikes': 6});
});

test('should return null for unspecified sum field', () async {
  final _sum = await collection.aggregate(sum('likes')).get();
  expect(_sum.getSum('dislikes'), isNull);
  expect(_sum.count, 3);
});

[atn832]

Great PR. It does not handle converted queries but it covers non-converted ones nicely. Thank you!

[ming-chu]

@atn832 Sorry I missed the converted queries, maybe we could create an issue to follow up later 🙇🏻