c# - how to efficiently Comparing two lists with 500k objects and strings -

so have main directory sub folders , around 500k images. know alot of theese images not exist in database , want know ones can delete them.

this code have far:

var listofadpicturenames = imagedb.getalladpicturenames();  var listwithfilesfromimagefolder = imagedirsearch(adpicturespath);  var result = listwithfilesfromimagefolder.where(p => !listofadpicturenames.any(q => p.filename == q));  var differencelist = result.tolist(); 

listofadpicturenames of type list<string>

here model im returing imagedirsearch:

public class checknotusedadimagesmodel {     public list<imagedirmodel> listwithunusedadimages { get; set; } }  public class imagedirmodel {     public string filename { get; set; }     public string path { get; set; } } 

and here recursive method images folder.

private list<imagedirmodel> imagedirsearch(string path)         {             string adpicturespath = configurationmanager.appsettings["adpicturespath"];             list<imagedirmodel> files = new list<imagedirmodel>();  try {     foreach (string f in directory.getfiles(path))     {         var model = new imagedirmodel();         model.path = f.tolower();         model.filename = path.getfilename(f.tolower());         files.add(model);     }     foreach (string d in directory.getdirectories(path))     {         files.addrange(imagedirsearch(d));     } } catch (system.exception excpt) {     throw new exception(excpt.message); }  return files; 

}

the problem have row:

var result = listwithfilesfromimagefolder.where(p => !listofadpicturenames.any(q => p.filename == q)); 

takes on hour complete. want know if there better way check in images folder if there images there doesn't exist in database.

here method image names database layer:

    public static list<string> getalladpicturenames()     {         list<string> listwithalladfilenames = new list<string>();          using (var db = new databaselayer.dbentities())         {             listwithalladfilenames = db.ad_pictures.select(b => b.filename.tolower()).tolist();         }            if (listwithalladfilenames.count < 1)             return new list<string>();          return listwithalladfilenames;     } 

perhaps except you're looking for. this:

var filesinfoldernotindb = listwithfilesfromimagefolder.select(p => p.filename).except(listofadpicturenames).tolist(); 

should give files exist in folder not in database.