In the MongoDB driver for C#, I want to filter and then sort my collection with the following rules:

First: Sort the documents in descending order based on “toCompareDate” (which is not an actual field in the documents). “toCompareDate” is postedDate if postedDate is not null; otherwise, it is createdDate.
Second: If “toCompareDate” values are equal, prioritize the documents where postStatus is 4.
Can you help me with this?

Thank you so much!

I have tried the following:

public class Program
{
    private static async Task Main(string[] args)
    {
        var client = new MongoClient("your_connection_string");
        var database = client.GetDatabase("your_database_name");
        var collection = database.GetCollection<Post>("Post");

        int page = 1; 
        int limit = 10; 
        int skip = (page - 1) * limit;

        var sortByStatus = new BsonDocument
        {
            {
                "sortOrder", new BsonDocument
                {
                    { "$cond", new BsonArray
                        {
                            new BsonDocument("$eq", new BsonArray { "$PostStatus", 4 }),
                            1,
                            2
                        }
                    }
                }
            }
        };

        var pipeline = new[]
        {
            new BsonDocument("$addFields", sortByStatus),
            new BsonDocument("$sort", new BsonDocument("sortOrder", 1)),
            new BsonDocument("$skip", skip),
            new BsonDocument("$limit", limit),
            new BsonDocument("$project", new BsonDocument("sortOrder", 0))
        };

        var result = await collection.Aggregate<BsonDocument>(pipeline).ToListAsync();

        foreach (var document in result)
        {
            Console.WriteLine(document);
        }
    }
}

But the result does not prioritize PostStatus 4.