title: Multi-field queries using C# driver for MongoDB
body: <p>I'm having trouble figuring out syntax for what I'm trying to accomplish. As stated I'm using the C# driver for MongoDB.</p>
  
  <p>I have a User entity defined as</p>
  
  <pre><code>[BsonIgnoreExtraElements]
  public class User : MongoEntity
  {
      [BsonElement]
      public string Username { get; set; }
  
      [BsonElement]
      public string Password { get; set; }
  
      [BsonElement]
      public string Email { get; set; }
  }
  </code></pre>
  
  <p>I also have a UserService class that performs actions against the User collection in my mongo database. Below is an example of how i'm creating a real simple login example.</p>
  
  <pre><code>public UserPresentation Login(string username, string password)
  {
      var entityQuery = Query&lt;User&gt;.EQ(e =&gt; e.Username, username.ToUpper());
  
      var entity = this.MongoConnectionHandler.MongoCollection.FindOne(entityQuery);
  
      return (entity != null &amp;&amp; entity.Id.ToString().Length &gt; 0 &amp;&amp; entity.Password == password) ? new UserPresentation(entity) : null;
  }
  </code></pre>
  
  <p>This works, however my question is... instead of creating a Query that only looks for Username == username, returning the element and then comparing the password in an if statement, can I somehow append more fields to the intial <code>entityQuery</code> object.</p>