What is the effect of AsEnumerable() on a LINQ Entity?

Question

Reading the questions here and here has given me some insight into the situation, and it seems like using the AsEnumerable is memory consuming. Is there a better way to do this LINQ and the way it is done now, is the data that comes out reliable?

Removing the AsEnumerable results in a "Local sequence cannot be used in LINQ to SQL implementations of query operators except the Contains operator."

var results = from p in pollcards.AsEnumerable()                           join s in spoils.AsEnumerable() on new { Ocr = p.OCR, fileName = p.PrintFilename } equals new { Ocr = s.seq, fileName = s.inputFileName }                           where p.Version == null                           orderby s.fileOrdering, s.seq                           select new ReportSpoilsEntity                           {                               seq = s.seq,                               fileOrdering = s.fileOrdering,                               inputFileName = s.inputFileName,                               Ocr = p.OCR,                               ElectorName = p.ElectorName                           }; 

Answer 1

AsEnumerable() is effectively a cast to IEnumerable<T>, which makes member resolution find members of Enumerable instead of Queryable. It's usually used when you want to force part of a query to run as SQL (or similar), and the remainder to run using LINQ to Objects.

See my Edulinq blog post on it for more information.

Now you've actually got two calls to AsEnumerable. I can see how removing the first but not the second could cause problems, but have you tried removing both?

var results = from p in pollcards               join s in spoils                  on new { Ocr = p.OCR, fileName = p.PrintFilename }                   equals new { Ocr = s.seq, fileName = s.inputFileName }               where p.Version == null               orderby s.fileOrdering, s.seq               select new ReportSpoilsEntity               {                   seq = s.seq,                   fileOrdering = s.fileOrdering,                   inputFileName = s.inputFileName,                   Ocr = p.OCR,                   ElectorName = p.ElectorName               };