elasticsearch NEST get nested document

Question

situation is this. I have in elastic a group. each of these groups have a nested list of items. Both group and items have an attribute named serial, which are unique. I get a serial for the group and a serial for item, and with those 2 items i'm supposed to return the item.

Currently i'm doing it the following way:

public item findItem(string groupSerial, string itemSerial)
    {
        var searchResponse = _elasticClient.Search<Group>(s => s
            .Index(_config.groupIndexName)
            .Query(q => q
                .ConstantScore(cs => cs
                    .Filter(f => f
                        .Term(t => t
                            .Field(fi => fi.serial)
                            .Value(groupSerial)
                        )
                    )
                )
            ).Query(q => q
                .Nested(c => c
                    .InnerHits(i => i.Explain())
                    .Path(p => p.items)
                    .Query(nq => nq.Term(t => t
                        .Field(field => field.items.First().serial)
                        .Value(itemSerial)))))
        );

        var result = searchResponse.Documents.FirstOrDefault();

        return result?.items.Find(item => item.serial == itemSerial);
    }

I get the feeling that there is supposed to be a more efficient way. Like getting the item straight from the search in elastic. Does anyone know how?