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mongodb

Guid Serialization SubTypes

The mongodb guid representation mode is causing some issues, Where it has to be explicitly specified to 'standard' in the graph apis.

  • What is the default used in mongodb 6 and the C# driver associated with it?
  • What is the default now in mongodb 8 and the C# driver associated with it?
  • What representation mode is best and what should be used?
  • Does changing to a new one result in any backward compatibility issues?
Solution

  • To shed some light on the issues: first, there is no "MongoDB C# Driver associated with a MongoDB version". Sure, a driver version might cut support for very old MongoDB versions, but the current version of MongoDB C# Driver (v3.1) supports a wide range of MongoDB versions. You can check the compatibility in this part of the documentation.

    The problem with the GUID representation was that some time ago, the drivers for specific languages/environments serialized a GUID in a different way. So the Java driver wrote the GUID in a different binary form than the C# Driver did. This made cross-language interoperation very difficult; if you had written the GUID with Java, it was hard to read it with C#, and vice versa.

    As a solution, MongoDB introduced a new binary subtype (4) that is used for GUIDs and is implemented in the same way for drivers across all languages.

    In newer C# Driver versions, MongoDB has moved on from binary subtype 3 to binary subtype 4, but also acknowledged that it is hard to find a default due to the various ways a GUID could be written to database. Hence, you need to configure the serialization of GUIDs in your application either on a per-property basis or globally. This is good news as it finally allowed to handle each property in a specific way and solved a lot of problems if you had mixed GUIDs in your database that have been serialized with subtype 3 and different languages.

    For new projects, you should always use binary subtype 4 (GuidRepresentation.Standard) as it is the serialization that is interoperable over all language drivers. If you access an existing database that contains GUIDs written with binary subtype 3, you need to configure those properties to use the corresponding GUID representation mode to be able to read/write the data correctly.

    Also, if you decide for a property to use a specific GUID representation mode now and change it later, you might end up with serialization problems.

    Please see this piece of the documentation on how to configure the representation mode for GUID on a per-property basis or globally.