Transaction readConcern silently dropped when RunCommand includes explicit readConcern

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    • Type: Improvement
    • Resolution: Unresolved
    • Priority: Unknown
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    • Affects Version/s: None
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    • Dotnet Drivers
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      1. What would you like to communicate to the user about this feature?
      2. Would you like the user to see examples of the syntax and/or executable code and its output?
      3. Which versions of the driver/connector does this apply to?

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      1. What would you like to communicate to the user about this feature? 2. Would you like the user to see examples of the syntax and/or executable code and its output? 3. Which versions of the driver/connector does this apply to?
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      The transaction path in CreateType0Section uses AddIfNotAlreadyAdded for readConcern, which silently drops the transaction's readConcern if the command already has one (e.g. via CreateCommand). Ideally it should use extraElements.Add() like the snapshot path, so the transaction's readConcern always wins. It doesn't hit any errors today because GetReadConcernForCommand returns null for IsInTransaction and there's a separate GetReadConcernForFirstCommandInTransaction, but a raw RunCommand with an explicit readConcern inside a transaction would get the wrong precedence. 

      Repro:

      using var session = client.StartSession();
session.StartTransaction(new TransactionOptions(
    readConcern: ReadConcern.Majority,
    writeConcern: WriteConcern.WMajority));

var command = new BsonDocument
{
    { "find", "txn_readconcern_test" },
    { "readConcern", new BsonDocument("level", "local") }
};
database.RunCommand<BsonDocument>(session, command);

session.CommitTransaction();

var findEvent = eventCapturer.Events.OfType<CommandStartedEvent>().First();
var sentReadConcern = findEvent.Command["readConcern"].AsBsonDocument;

// This assertion fails (it sends "local" instead of "majority")
sentReadConcern["level"].AsString.Should().Be("majority");

            Assignee:
            Oleksandr Poliakov
            Reporter:
            Kyra Ramesh Krishna
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              Created:
              Updated: