title: Upserting in Mongo DB using official C# driver
body: <p>In the official documentation of mongodb they mention upserts, so it would be really nice to write an upsert command instead of:</p>
  
  <pre><code>if (_campaignRepo.Exists(camp))
  {
      _campaignRepo.DeleteByIdAndSystemId(camp);
  }
  
  _campaignRepo.Save(camp);
  </code></pre>
  
  <p>something which would implement that logic on the db level if it is possible. So what is the way to do an upsert if there is one?</p>