How to do an upsert with MongoDB 2.0?

Pass an instance of UpdateOptions as the options parameter in UpdateOneAsync(filter, update, options), e.g.:

collection.UpdateOneAsync(p => p.Id == user.Id,     Builders<User>.Update.Set(p => p.Name, "John"),     new UpdateOptions { IsUpsert = true });

EDIT

To replace the document, call ReplaceOneAsync instead:

collection.ReplaceOneAsync(p => p.Id == user.Id,     user,     new ReplaceOptions { IsUpsert = true });

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