Convert .NET Guid to MongoDB ObjectID

Question

How can I convert a .NET GUID to a MongoDB ObjectID (in C#). Also, can I convert it back again to the same GUID from the ObjectID?

Answer 1

You can't convert ObjectId into GUID and vice versa, because they are two different things(different sizes, algoritms).

You can use any type for mongoDb _id including GUID.

For example in official c# driver you should specify attribute [BsonId]:

[BsonId] public Guid Id {get;set;}  [BsonId] public int Id {get;set;} 

ObjectId:

A BSON ObjectID is a 12-byte value consisting of a 4-byte timestamp (seconds since epoch), a 3-byte machine id, a 2-byte process id, and a 3-byte counter. Note that the timestamp and counter fields must be stored big endian unlike the rest of BSON. This is because they are compared byte-by-byte and we want to ensure a mostly increasing order.

GUID:

The value of a GUID is represented as a 32-character hexadecimal string, such as {21EC2020-3AEA-1069-A2DD-08002B30309D}, and is usually stored as a 128-bit integer

Answer 2

FYI You can convert from an ObjectId to a Guid

    public static Guid AsGuid(this ObjectId oid)     {         var bytes = oid.ToByteArray().Concat(new byte[] { 5, 5, 5, 5 }).ToArray();         Guid gid = new Guid(bytes);         return gid;     }      /// <summary>     /// Only Use to convert a Guid that was once an ObjectId     /// </summary>     public static ObjectId AsObjectId(this Guid gid)     {         var bytes = gid.ToByteArray().Take(12).ToArray();         var oid = new ObjectId(bytes);         return oid;     }