title: Insert Dictionary into MongoDB with c# driver
body: <p>I am in a situation where I can't predict which fields my MongoDB document is going to have. So I can no longer create an object with an <code>_id</code> field of type <code>BsonID</code>. 
  I find it very convenient to create a Dictionary (HashTable) and add my DateTime and String objects inside, as many times as I need it. </p>
  
  <p>I then try to insert the resulting Dictionary object into MongoDb, but default serialization fails.</p>
  
  <p>Here's my object of Type HashTable (like a Dictionary, but with varied types inside):</p>
  
  <pre><code>{ "_id":"",
  "metadata1":"asaad",
  "metadata2":[],
  "metadata3":ISODate("somedatehere")}
  </code></pre>
  
  <p>And the error from the driver I get is:</p>
  
  <blockquote>
    <p>Serializer DictionarySerializer expected serialization options of type DictionarySerializationOptions, not DocumentSerializationOptions</p>
  </blockquote>
  
  <p>I googled it, but couldn't find anything useful. What am I doing wrong?</p>