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POLINQ enumeration of local dirves using DriveInfo
 

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    <p>I know there are many ways to accomplish what I am trying to do here, but I wanted to try it with LINQ, and am seeing some odd (to me) results. Hoping someone here has some wisdom to offer me.</p> <p>Goal is to find the drive on the local machine where we execute with the most available free space that has been formatted to NTFS file system, excluding the %SystemDrive% volume if possible. Another caveat is that drives that are assigned a volume letter, but have not yet been formatted must be excluded from the candidate pool. This is an edge case, but one customer has already encountered it.</p> <p>So, I am trying:</p> <pre><code>string systemDrive = Environment.GetEnvironmentVariable("SystemDrive") + "\\"; List&lt;DriveInfo&gt; localDrives = DriveInfo.GetDrives().ToList(); var bestAPIDataDrives = from localDrive in localDrives orderby localDrive.AvailableFreeSpace descending where localDrive.DriveType == DriveType.Fixed &amp;&amp; localDrive.DriveFormat == "NTFS" &amp;&amp; localDrive.RootDirectory.FullName != systemDrive &amp;&amp; localDrive.IsReady select localDrive.RootDirectory.FullName; string path = String.Empty; if (bestAPIDataDrives.Count() == 0) { // there is only a system drive available, use it anyway. path = systemDrive; } else { path = bestAPIDataDrives.ElementAt(0).ToString(); } </code></pre> <p>When I get to the bestAPIDataDrives.Count() reference, I get an IOException with Message property set to "The device is not ready".</p> <p>I don't see why this is happening because I have the localDrive.IsReady test in the LINQ query, or at least I think I do.</p>
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    1. USjoebalt
    1. USjoebalt
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    1. COMarc has answered the real question, so two code review comments: This code actually executes the query twice, once to count and again to find the first element. You also do not have to ToString a string. Everything after building the query can be replaced with `string path = bestAPIDataDrives.FirstOrDefault() ?? systemDrive`. You also do not need to create a List from the results of `DriveInfo.GetDrives()`, and can say `IEnumerable<DriveInfo> localDrives = DriveInfo.GetDrives()`.
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      1. USChris Pitman
    2. CO@Chris - good spot; I definitely agree - should use `FirstOrDefault()` here (and nothing else; that covers both `Count()` and `ElementAt()`, much more efficiently)
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      1. USMarc Gravell
    3. COGood advice again, all. Many thanks. Will update the solution with these code review items.
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      1. USjoebalt
 

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