MongoDB C# Get latest document from group

Question

I have a group of statuses of pretend payments, each with a payment ID.

I want to get the latest status for each payment ID. The test I have creates some dummy data

Answer 1

This is how I've achieved it. There has to be a better way though.

[Test]
public void GetPaymentLatestStatuses()
{
    var client = new TestMongoClient();

    var database = client.GetDatabase("payments");

    var paymentRequestsCollection = database.GetCollection("paymentRequests");

    var statusesCollection = database.GetCollection("statuses");

    var payment = new BsonDocument { { "amount", RANDOM.Next(10) } };

    paymentRequestsCollection.InsertOne(payment);

    var paymentId = payment["_id"];

    var receivedStatus = new BsonDocument
                         {
                             { "payment", paymentId },
                             { "code", "received" },
                             { "date", DateTime.UtcNow }
                         };
    var acceptedStatus = new BsonDocument
                         {
                             { "payment", paymentId },
                             { "code", "accepted" },
                             { "date", DateTime.UtcNow.AddSeconds(+1) }
                         };
    var completedStatus = new BsonDocument
                          {
                              { "payment", paymentId },
                              { "code", "completed" },
                              { "date", DateTime.UtcNow.AddSeconds(+2) }
                          };

    statusesCollection.InsertMany(new[] { receivedStatus, acceptedStatus, completedStatus });

    var groupByPayments = new BsonDocument
                          {
                              { "_id", "$payment" },
                              { "id", new BsonDocument { { "$first", "$_id" } } }
                          };

    var sort = Builders.Sort.Descending(document => document["date"]);

    var statuses = statusesCollection.Aggregate().Sort(sort).Group(groupByPayments).ToList();

    var statusIds = statuses.Select(x => x["id"]);

    var completedStatusDocumentsFilter =
        Builders.Filter.Where(document => statusIds.Contains(document["_id"]));

    var statusDocuments = statusesCollection.Find(completedStatusDocumentsFilter).ToList();

    foreach (var status in statusDocuments)
    {
        Assert.That(status["code"].AsString, Is.EqualTo("completed"));
    }
}