MongoDB c#创建角色？

我正在尝试与c#driver一起创建一个角色。 谁能告诉我怎么做

我试过几种类似的方法：

var command = new CommandDocument( 
                new BsonDocument
                {
                    { "createRole", "Testentity_read" },
                    { "privileges", new BsonArray(new BsonDocument
                        {
                            {
                                "resource", new BsonDocument
                                {
                                    {"db", "MyDb"},
                                    {"collection", "Testentity"}
                                }
                            },
                            {
                                "actions", new BsonArray {"read"}
                            }
                        })},
                    { "roles", new BsonArray()}
                }
            );

            var result = _database.RunCommand(command);

但总是有这样的例外：

".NET type MongoDB.Bson.BsonElement cannot be mapped to a BsonValue."

---

我发现了如何从C#driver创建角色

以下是我尝试做的：

var command = new CommandDocument
{
    {
        "createRole", "Testentity_find"
    },
    { 
        "privileges", new BsonArray
        {
            new BsonDocument
            {
                {
                   "resource", new BsonDocument
                    {
                        {"db", "MyDb"},
                        {"collection", "Testentity"}
                    }
                },
                {

                    "actions", new BsonArray {"find"}
                }
            }
        }
    },
    { "roles", new BsonArray()}
};