.NET 10.0'daki yenilikler [23]: Yeni LINQ operatörleri LeftJoin() ve RightJoin()

.NET'in son sürümlerinde olduğu gibi, Microsoft yine .NET 10.0'da Dil Tümleşik Sorgu (LINQ) için mevcut yapıları basitleştiren yeni operatörler sağlıyor. Bu sefer yanında LeftJoin() VE RightJoin() biri küme teorisinden, diğeri ilişkisel veritabanlarından olmak üzere iki temel operatör. Bu konuyla ilgili daha fazla bilgiyi GitHub'daki ilgili sayıda bulabilirsiniz.

Aslında bu işlemler LINQ'da zaten mümkündü, ancak gruplandırma kullanmanın zorluğu vardı GroupJoin() VE SelectMany() birlikte DefaultIfEmpty(). Yeni yöntemler LeftJoin() VE RightJoin() sınıflar arasındaki birleştirme örneğini kullanan aşağıdaki kod gibi kullanımı kolaylaştırın Company ve web sitesi şunu gösteriyor:

public void LeftRightJoin()
{
 CUI.Demo();
 
 Company[] companies =
 [
   new Company{ ID = 1, Name = "www.IT-Visions.de" },
   new Company{ ID = 2, Name = "Software & Support" },
   new Company{ ID = 3, Name = "Heise Gruppe GmbH & Co. KG" },
   new Company{ ID = 4, Name = "Startup i.Gr." } // hat noch keine Website
 ];
 
 Website[] websites =
 [
   new Website{ CompanyID = 1, URL = "www.IT-Visions.de" },
   new Website{ CompanyID = 1, URL = "www.dotnet10.de" },
   new Website{ CompanyID = 2, URL = "www.entwickler.de" },
   new Website{ URL = "www.Microsoft.com" }, // Diese kleine ;-) Firma ist noch nicht angelegt...
   new Website{ CompanyID = 3, URL = "Haber" },
 ];
 
 // ### LeftJOIN ALT ############################################################################
 
 CUI.H2("--- Alle Firmen mit ggf. vorhandenen Websites via LeftJoin ALT (GroupJoin+SelectMany) seit .NET Framework 3.5 ---");
 
 var AllCompaniesWithWebsitesSetOld = companies
     .GroupJoin(websites,
                c => c.ID,
                w => w.CompanyID,
                (c, websites) => new { Company = c, Websites = websites })
     .SelectMany(
         x => x.Websites.DefaultIfEmpty(),  // Falls keine Website existiert, wird `null` verwendet
         (c, w) => new WebsiteWithCompany
         {
          Name = c.Company.Name,
          URL = w.URL,   // Falls `w` null ist, bleibt URL null
          City = c.Company.City
         });
 
 foreach (var item in AllCompaniesWithWebsitesSetOld)
 {
  Console.WriteLine((item.Name != null ? item.Name + " " + item.City : "- keine Firma -").Trim() + " -> " + (item.URL ?? "- keine URL -"));
 }
 
 // ### LeftJOIN NEU ############################################################################
 
 CUI.H2("--- Alle Firmen mit ggf. vorhandenen Websites via LeftJoin NEU ab .NET 10.0 ---");
 var AllCompaniesWithWebsitesSet = companies.LeftJoin(websites,
  e => e.ID,
  e => e.CompanyID,
  (c, w) => new WebsiteWithCompany { Name = c.Name, City = c.City, URL = w.URL }
  );
 
 foreach (var item in AllCompaniesWithWebsitesSet)
 {
  Console.WriteLine((item.Name != null ? item.Name + " " + item.City : "- keine Firma -").Trim() + " -> " + (item.URL ?? "- keine URL -"));
 }
 
 // ### RightJoin ALT ############################################################################
 
 CUI.H2("--- Alle Websites mit ggf. vorhandenen Firmen via RightJoin ALT (GroupJoin+SelectMany) seit .NET Framework 3.5  ---");
 var WebsiteWithCompanySetOLD = websites
     .GroupJoin(companies,
                w => w.CompanyID,
                c => c.ID,
                (w, companies) => new { Website = w, Companies = companies })
     .SelectMany(
         x => x.Companies.DefaultIfEmpty(),  // Falls kein Unternehmen existiert -> null
         (w, c) => new WebsiteWithCompany
         {
          Name = c.Name,  // Falls `c` null ist, bleibt `Name` null
          City = c.City,   // Falls `c` null ist, bleibt `City` null
          URL = w.Website.URL
         });
 
 foreach (var item in WebsiteWithCompanySetOLD)
 {
  Console.WriteLine((item.Name != null ? item.Name + " " + item.City : "- keine Firma -").Trim() + " -> " + (item.URL ?? "- keine URL -"));
 }
 
 // ### RightJoin NEU ############################################################################
 
 CUI.H2("--- Alle Websites mit ggf. vorhandenen Firmen via RightJoin NEU ab .NET 10.0 ---");
 var WebsiteWithCompanySet = companies.RightJoin(websites,
     e => e.ID,
     e => e.CompanyID,
     (c, w) => new WebsiteWithCompany { Name = c.Name, City = c.City, URL = w.URL }
  );
 
 foreach (var item in WebsiteWithCompanySet)
 {
  Console.WriteLine((item.Name != null ? item.Name + " " + item.City : "- keine Firma -").Trim() + " -> " + (item.URL ?? "- keine URL -"));
 }
 
 // ### Zum Vergleich: Inner Join, den es seit .NET Framework 3.5 gibt
 CUI.H2("--- Alle Firmen, die Websites haben, via InnerJoin seit .NET Framework 3.5 ---");
 var CompaniesWithWebsitesSet = companies.Join(websites,
                                        c => c.ID,
                                        w => w.CompanyID,
                                        (c, w) => new WebsiteWithCompany
                                        {
                                         Name = c.Name,
                                         URL = w.URL,
                                         City = c.City
                                        });
 foreach (var item in CompaniesWithWebsitesSet)
 {
  Console.WriteLine((item.Name != null ? item.Name + " " + item.City : "- keine Firma -").Trim() + " -> " + (item.URL ?? "- keine URL -"));
 }
}

Microsoft'a göre yeni operatörler, önceki operatör kombinasyonlarına göre daha performanslı.

(Ben)