At the moment it is not obvious how to set a custom registry, such that it is used both when writing to mongo and reading with a cursor.

 

Bellow an example of what is I had to do to get this t work:

 
rb := bson.NewRegistryBuilder()

    cod := &UUIDCodec{}
    tUUID := reflect.TypeOf(uuid.UUID{})

    rb.RegisterDecoder(reflect.PtrTo(tUUID), bsoncodec.ValueDecoderFunc(cod.DecodeValue))
    rb.RegisterEncoder(reflect.PtrTo(tUUID), cod)

    reg := rb.Build()

    opt := &options.ClientOptions{
        Registry: reg,
        TopologyOptions: []topology.Option{
            topology.WithServerOptions(func(opts ...topology.ServerOption) []topology.ServerOption {
                return []topology.ServerOption{
                    topology.WithRegistry(func(r *bsoncodec.Registry) *bsoncodec.Registry

{                         return reg                     }

),
                }
            }),
        },
    }
 
Adding this or something similar as an example, or even pushing this code into the SetRegistry method of the mongo.Options would be helpful.

    client, err := mongo.NewClientWithOptions(url, opt)