title: Check if UI(Managed)Document is already in iCloud via URLForUbiquityContainerIdentifier+Path instead of NSMetadataQuery?
body: <p>I have a quite simple shoebox-style iOS app with <strong>1</strong> single <strong>Core Data</strong> database (as a <strong>UIManagedDocument</strong>) and thought about trying to add <strong>iCloud</strong> support.</p>
  
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  <p>I of course have to <strong>check if</strong> there is already an <strong>existing</strong> database <strong>in the cloud</strong> *<em>before creating a new UIManagedDocument at startup</em>*, saving/opening it, etc.</p>
  
  <p>As i <strong>already know the filename</strong> and that there's either 1 document or no document at all, I didn't really get if I had to</p>
  
  <ol>
  <li><p>start a <strong>NSMetaDataQuery</strong> with a predicate for the <strong>exact filename</strong>
  and then <strong>get</strong> the <strong>fileURL from the result</strong> (and download it
  explicitly?) and open it if there is one, or </p></li>
  <li><p>just use <code>[[NSFileManager defaultManager] fileExistsAtPath:self.iCloudDBURL]</code>
  with <code>iCloudDBURL</code> created from <strong>URLForUbiquityContainerIdentifier</strong> + appending ? Is this URL only a local one and doesn't check the "real" cloud automatically?</p></li>
  </ol>
  
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  <p>I know the use of UIManagedDocument might not be the "right" way for this kind of app, but I thought it'd easier and I could try..</p>