//4a1. Lấy all row document, ko filter
public string DocumentFind_All()
{
    // Replace the uri string with your MongoDB deployment's connection string.
    var client = new MongoClient(
        "mongodb://localhost:27017/?readPreference=primary&appname=MongoDB%20Compass&directConnection=true&ssl=false"
    );

    string re = "";

    //lấy database
    var database = client.GetDatabase("HvDadabase");
    //Lấy List Collection
    var collection = database.GetCollection<BsonDocument>("HvCars");

    //select all , ko filter
    //var filter = Builders<BsonDocument>.Filter.Eq("name", name);
    var documentList = collection.Find(new BsonDocument()).ToList();

    foreach (var row in documentList)
    {
        re += row;
    }

    return re;
}