LINQ to Entities - Sono supportati solo costruttori e inizializzatori senza parametri

C# 4.0

Nella seguente query LINQ l’ordinamento si basa sul campo db di tipo “stringa” quindi un ordinamento errato perché 1.0.0.11 come stringa precede 1.0.0.9:

                    var query = from c in dc.Customer

                         join cp in dc.CustomerPackage

                             on c.Id equals cp.IdCustomer

                         join p in dc.Package

                             on cp.IdPackage equals p.Id

                         where c.Code == customerCode

                               && c.ChainCode == chainCode

                               && c.StoreCode == storeCode

                               && cp.DownloadDate == null

                         orderby p.Version

                         select p;

Così generava l’eccezione “Sono supportati solo costruttori e inizializzatori senza parametri”:

                    var query = from c in dc.Customer

                         join cp in dc.CustomerPackage

                             on c.Id equals cp.IdCustomer

                         join p in dc.Package

                             on cp.IdPackage equals p.Id

                         where c.Code == customerCode

                               && c.ChainCode == chainCode

                               && c.StoreCode == storeCode

                               && cp.DownloadDate == null

                         orderby new Version(p.Version)

                         select p;

Così generava sempre l’eccezione

                    var query = (from c in dc.Customer

                        join cp in dc.CustomerPackage

                            on c.Id equals cp.IdCustomer

                        join p in dc.Package

                            on cp.IdPackage equals p.Id

                        where c.Code == customerCode

                              && c.ChainCode == chainCode

                              && c.StoreCode == storeCode

                              && cp.DownloadDate == null

                         select p).OrderBy(p => new Version(p.Version));

Così invece funziona perché passando per il metodo ToList() credo che l’OrderBy lo faccia attraverso la collezione di oggetti e non più attraverso la query entity

                    var query =

                        (from c in dc.Customer

                         join cp in dc.CustomerPackage

                             on c.Id equals cp.IdCustomer

                         join p in dc.Package

                             on cp.IdPackage equals p.Id

                         where c.Code == customerCode

                               && c.ChainCode == chainCode

                               && c.StoreCode == storeCode

                               && cp.DownloadDate == null

                         select p).ToList().OrderBy(p => new Version(p.Version));

Per questa segnalazione va un particolare ringraziamento a Giovanni Canacci, detto anche Giò.