Why is Enumerable.Count() throwing `InvalidOperationException` for converting `null` to `bool`? RSS

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  camitz

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  Why is Enumerable.Count() throwing `InvalidOperationException` for converting `null` to `bool`?

  Feb 01, 2010 07:54 PM|LINK

  The following goes wrong.
  

  if (user.Friends.Count() == 0)

      ....

  
  

  It throws System.InvalidOperationException: The value null not be assigned a member of type System.Boolean since it is a value type that cannot have the value null

  Part of the answer is that I expect user.Friends to be empty. It is a WhereSelectEnumerableIterator returned from a linq to sql call and when it's not empty the above works fine.

  (Also open on stackoverflow.)
  

  LinqToSql ASp.net-mvc

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  ignatandrei

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  Re: Why is Enumerable.Count() throwing `InvalidOperationException` for converting `null` to `bool...

  Feb 01, 2010 10:36 PM|LINK

  this isn't a MVC discussion - I think it is a L2S or EF discussion. And maybe the count of friends is null when performing SQL translate - and therefore can not be translated ...

  And maybe your Friends have a bool property ...
  

  My .NET blog : http://msprogrammer.serviciipeweb.ro/ |2012 Programmer tools
  • Edited by KeFang Chen - MSFT on Feb 04, 2010 04:31 AM
  • Edited by KeFang Chen - MSFT on Feb 04, 2010 04:31 AM
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  PaulBlamire

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  Re: Why is Enumerable.Count() throwing `InvalidOperationException` for converting `null` to `bool...

  Feb 01, 2010 11:21 PM|LINK

  if (user.Friends == null || user.Friends.Count()==0)

  Or add a public partial class User and add a has friends property
  

  public bool HasFriends
  {
     get
     {
       return (Friends != null && Friends.Any())
     }
  }

  then

  if (!user.HasFriends)

  Paul
  

  http://pabloblamirez.blogspot.com - When you ask a question, remember to click "mark as answered" when you get a reply which answers your question; this ensures the right forum member gets credit below for being helpful (and makes search more relevant too).
  • Marked as answer by KeFang Chen - MSFT on Feb 04, 2010 04:31 AM