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LINQ Example

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The following example shows a couple of LINQ Queries in X#

//references:
//System.dll
//System.Core.dll
//System.Linq.dll  
USING System.Collections.Generic    
USING System.Linq
USING STATIC System.Console
 
FUNCTION Start AS VOID
  VAR oDev   := GetDevelopers()
  VAR oC     := GetCountries()
  VAR oAll   := FROM D       IN oDev  ;
                JOIN C       IN oC ON D:Country EQUALS C:Name   ;
                ORDERBY D:LastName  ;
                SELECT CLASS {D:Name, D:Country, C:Region}     // Anonymous class !
  // The type of oAll is IOrderedEnumerable<<>f__AnonymousType0<Developer,Country>>  
  // We prefer the VAR keyword!
       
  VAR oGreek := FROM Developer IN oDev ;
          WHERE Developer:Country == "Greece" ;
          ORDERBY Developer:LastName DESCENDING ;
          SELECT Developer                  
  // The type of oGreek is IOrderedEnumerable<Developer>
  // We prefer the VAR keyword!
 
  VAR oCount :=   FROM Developer IN oDev ;
          GROUP Developer BY Developer:Country INTO NewGroup ;
          ORDERBY NewGroup:Key SELECT NewGroup      
  // The type of oCount is IOrderedEnumerable<<IGrouping<string,Developer>>
  // We prefer the VAR keyword!
 
  WriteLine(e"X# does LINQ!\n")
  WriteLine(e"All X# developers (country+lastname order)\n")    
  FOREACH VAR oDeveloper IN oAll
     WriteLine("{0} in {1}, {2}",oDeveloper:Name, oDeveloper:Country, oDeveloper:Region)
  NEXT                                  
   
  WriteLine(e"\nGreek X# Developers (descending lastname)\n")    
  FOREACH oDeveloper AS Developer IN oGreek
     WriteLine(oDeveloper:Name)
  NEXT                        
 
  WriteLine(e"\nDevelopers grouped per country\n")
 
  FOREACH VAR country IN oCount
     WriteLine(i"{country.Key}, {country.Count()} developer(s)")
    FOREACH VAR oDeveloper IN country
        WriteLine("  " + oDeveloper:Name)
    NEXT
  NEXT                        
  WriteLine("Enter to continue")
  ReadLine()
  RETURN
 
 
FUNCTION GetDevelopers AS IList<Developer>        
  // This function uses a collection initializer for the List of Developers
  // and Object initializers for the Developer Objects
  VAR oList := List<Developer>{}    { ;
                          Developer{}{ FirstName  := "Chris", LastName := "Pyrgas", Country := "Greece"},;
                          Developer{}{ FirstName  := "Robert", LastName := "van der Hulst", Country := "The Netherlands"},;
                          Developer{}{ FirstName  := "Fabrice", LastName := "Foray", Country := "France"},;
                          Developer{}{ FirstName  := "Nikos", LastName := "Kokkalis", Country := "Greece"} ;
                       }
  RETURN oList
 
FUNCTION GetCountries AS IList<Country>
  // This function uses a collection initializer for the List of Counties
  // and Object initializers for the Country Objects
  VAR oList := List<Country>{}{ ;
                       Country{} {Name := "Greece",       Region := "South East Europe"},;
                       Country{} {Name := "France",       Region := "West Europe"},;
                       Country{} {Name := "The Netherlands",    Region := "North West Europe"} ;
                    }
  RETURN oList  
     
CLASS Developer                  
  PROPERTY Name       AS STRING GET FirstName + " " + LastName
  PROPERTY FirstName   AS STRING AUTO
  PROPERTY LastName   AS STRING AUTO
  PROPERTY Country   AS STRING AUTO
END CLASS
 
CLASS Country
  PROPERTY Name       AS STRING AUTO
  PROPERTY Region   AS STRING AUTO
END CLASS