title: Import part with specific meta data using MEF Preview 5
body: <p>I have a export defined as as follows in MEF preview 5</p>
  
  <pre><code>[ExportMetadata("Application", "CheckFolderApplication")]
  [Export(typeof(ExtendedArtifactBase))]
  public class CheckFolderArtifact2 : ExtendedArtifactBase
  { ...
  </code></pre>
  
  <p>Then I <strong>only</strong> want those imports with the "Application" "CheckFolderApplication" metadata. To currenly do that I read <em>all</em> the imports and then filter the result.  </p>
  
  <pre><code>[Import(typeof(ExtendedApplicationBase))]
  private ExportCollection&lt;IApplication&gt; _applications { get; set; }
  
  public IApplication GetApplication(string applicationName)
  {
      return _applications.Single(a =&gt; a.GetExportedObject().Name == applicationName).GetExportedObject();
   }
  </code></pre>
  
  <p>This feels really inefficient. What if I have thousands of plug-ins - do I have to read them all via MEF to just get one with the right metadata? If so how do you cache the result?</p>