title: MongoDB (server v 2.6.7) with C# driver 2.0: How to get the result from InsertOneAsync
body: <p>I am testing MongoDB (server v 2.6.7)  with the C# driver 2.0.</p>
  
  <p>When I am using the insert function <code>InsertOneAsync</code> for a document with an <code>_id</code> which exists I am expecting an error like the one you get from the Mongo shell:</p>
  
  <blockquote>
  <pre><code>WriteResult({
      "nInserted" : 0,
      "writeError" : {
              "code" : 11000,
              "errmsg" : "insertDocument :: caused by :: 11000 E11000 duplicate key error index: mydb.Commands.$_id_  dup key: { : 0.0 }"
      }})
  </code></pre>
  </blockquote>
  
  <p>But the problem is that the insert with the C# driver does not throw an exception and I can not find the <code>WriteResult</code> for the insert.
  When I look in the database it seems nothing have happened.</p>
  
  <p>So my question is what to expect from <code>InsertOneAsync</code> when inserting an existing <code>_id</code>? </p>
  
  <p>The code in Visual Studio: </p>
  
  <pre><code>IMongoCollection&lt;BsonDocument&gt; commandsCollection = db.GetCollection&lt;BsonDocument&gt;("Commands");
  var bson = new BsonDocument
          {
              {"_id", i.Value},
              {"label", i.Key}
          };
  commandsCollection.InsertOneAsync(bson);
  </code></pre>