Get _id of an inserted document in MongoDB?

Question

say I have a product listing. When I add a new product I save it using something like

var doc=products.Insert(p);

The pro

Answer 1

If you know the type of ID you can do something like this:

public static TId GetId(this BsonDocument document) where TId : struct
{
    if (document == default(BsonDocument))
    {
        throw new ArgumentNullException("document");
    }

    var id = document["_id"];

    object idAsObject;

    if (id.IsGuid)
    {
        idAsObject = (object)id.AsGuid;
    }
    else if (id.IsObjectId)
    {
        idAsObject = (object)id.AsObjectId;
    }
    else
    {
        throw new NotImplementedException(string.Format("Unknown _id type \"{0}\"", id.BsonType));
    }

    var idCasted = (TId)idAsObject;

    return idCasted;
}

Use it like this:

Guid idOfDoc = myBsonDocument.GetId();

Still you should prefere have a dedicated property as in the chosen answer...