Imar,

Thanks as always for the insight. A...

2009-02-01T10:32:00.000-05:00

Imar,

Thanks as always for the insight. As I'm still quite new to LINQ, I hadn't yet explored the ToList() method. I'll give that a try. I have used the SingleOrDefault() method. Very handy. In this example, I only need to check that the file exists, no need to get any more details. I'll make some changes and profile it.

Hi Peter,

The deferred execution model is b...

2009-02-01T04:36:00.000-05:00

Hi Peter,

The deferred execution model is by design; usually it's good as it allows you to query other queries before executing them, enabling you to limit your final data set before hitting the database.

Your GetEnumerator solution is close; however, instead of that, you should call ToList and store the results in a variable. The following code ensues only a SELECT * query is executed once before the loop while counting is done locally in the loop:

int intPhotoCount;
string[] strFiles;
string dirPath = @"C:\SomePath";
strFiles = Directory.GetFiles(dirPath, "*.*");
var lstPhotos = (from p in _db.Photos select p).ToList();
for (int i = 0; i < strFiles.Length; i++)
{
intPhotoCount = (from p in lstPhotos
where p.FullPath.ToLower() == strFiles[i].ToLower()
select p).Count();
if (intPhotoCount == 0)
{
// do create photo stuff
}
}

Rather than getting the Count, you can also retrieve the actual Photo (or null) like this:

Photo myPhoto = (from p in lstPhotos
where p.FullPath.ToLower() == strFiles[i].ToLower()
select p).SingleOrDefault();

if (myPhoto != null)
{
// do create photo stuff
}

Finally, you could do some funny JOIN stuff like this:

string[] strFiles;
string dirPath = @"C:\SomePath";
strFiles = Directory.GetFiles(dirPath, "*.*");
var orphanedFiles = (from o in strFiles
join a in _db.Photos on o equals a.FullPath into myFiles
where !_db.Photos.Any(p => p.FullPath == o)
select o).ToList();

foreach (var orphanedFile in orphanedFiles)
{
// Work with file here
}

Your Profiler will go crazy and you'll see a lot of queries being executed; but it's cool that it works nonetheless....

Code formatting is not ideal here, but I am sure yo get the idea....

Cheers,

Imar

Comments on Compiled Thoughts: Adventures in LINQ: Deferred execution

Imar, Thanks as always for the insight. A...

Hi Peter,The deferred execution model is b...

Imar,

Thanks as always for the insight. A...

Hi Peter,

The deferred execution model is b...