title: Query with filter builder on nested array using MongoDB C# driver
body: <p>Consider the following object structure stored as documents:</p>
  
  <pre><code>public class Foo
  {
      public string Id { get; set; }
      public ICollection&lt;FooBar&gt; Bars { get; set; }
  
      // ...
  }
  
  public class FooBar
  {
      public string BarId { get; set; }
  
      // ...
  }
  </code></pre>
  
  <p>Using a LINQ-style query with the driver I can <code>Find</code> all <code>Foo</code> that contain a <code>FooBar</code> <code>BarId</code> like this:</p>
  
  <pre><code>var foos = await m_fooCollection.Find( f =&gt; f.Bars.Any( fb =&gt; fb.BarId == "123") ).ToListAsync();
  </code></pre>
  
  <p>How can I achieve this same query using the <a href="http://mongodb.github.io/mongo-csharp-driver/2.0/reference/driver/definitions/#filter-definition-builder" rel="noreferrer"><code>FilterDefinitionBuilder</code></a> instead of the in-line LINQ on <code>Find</code>?</p>