Chapter65:LinqtoObjects

LINQtoObjectsreferstotheuseofLINQquerieswithanyIEnumerablecollection.

Section65.1:UsingLINQtoObjectsinC#

AsimpleSELECTqueryinLinq

staticvoidMain(string[]args)

{

string[]cars={“VWGolf”,

“OpelAstra”,

“AudiA4”,

“FordFocus”,

“SeatLeon”,

“VWPassat”,

“VWPolo”,

“MercedesC-Class”};

varlist=fromcarincars

selectcar;

StringBuildersb=newStringBuilder();

foreach(stringentryinlist)

{

sb.Append(entry+”\n“);

}

Console.WriteLine(sb.ToString()); Console.ReadLine();

}

Intheexampleabove,anarrayofstrings(cars)isusedasacollectionofobjectstobequeriedusingLINQ.InaLINQ query, the from clause comes first in order to introduce the data source (cars) and the range variable (car). When the query is executed, the range variable will serve as a reference to each successive element in cars. Because the compiler can infer the type of car, you do not have to specify it explicitly

Whentheabovecodeiscompiledandexecuted,itproducesthefollowingresult:

SELECTwithaWHEREClause

varlist=fromcarincars

wherecar.Contains(“VW”)

selectcar;

TheWHEREclauseisusedtoquerythestringarray(cars)tofindandreturnasubsetofarraywhichsatisfiesthe

WHEREclause.

Whentheabovecodeiscompiledandexecuted,itproducesthefollowingresult:

GeneratinganOrderedList

varlist=fromcarincars

orderbycarascending

selectcar;

Sometimes it is useful to sort the returned data. The orderby clause will cause the elements to be sorted according to the default comparer for the type being sorted.

Whentheabovecodeiscompiledandexecuted,itproducesthefollowingresult:

Workingwithacustomtype

Inthisexample,atypedlistiscreated,populated,andthenqueried

publicclassCar

{

publicStringName{get;privateset;}

publicintUnitsSold{get;privateset;}

publicCar(stringname,intunitsSold)

{

Name=name;

UnitsSold=unitsSold;

}

}

classProgram

{

staticvoidMain(string[]args)

{

varcar1=newCar(“VWGolf”,270952);

varcar2=newCar(“OpelAstra”,56079);

varcar3=newCar(“AudiA4”,52493);

varcar4=newCar(“FordFocus”,51677);

varcar5=newCar(“SeatLeon”,42125);

var car6 = new Car(“VW Passat”, 97586);

varcar7=newCar(“VWPolo”,69867);

varcar8=newCar(“MercedesC-Class”,67549);

varcars=newList<Car>{

car1,car2,car3,car4,car5,car6,car7,car8}; var list

=fromcarincars

selectcar.Name;

foreach(varentryinlist)

{

Console.WriteLine(entry);

}

Console.ReadLine();

}

}

Whentheabovecodeiscompiledandexecuted,itproducesthefollowingresult:

Until now the examples don’t seem amazing as one can just iterate through the array to do basically the same. However, with the few examples below you can see how to create more complex queries with LINQ to Objects and achieve more with a lot less of code.

In the example below we can select cars that have been sold over 60000 units and sort them over the number of units sold:

varlist=fromcarincars

wherecar.UnitsSold>60000

orderbycar.UnitsSolddescending

selectcar;

StringBuildersb=newStringBuilder();

foreach(varentryinlist)

{

sb.AppendLine($”{entry.Name}-{entry.UnitsSold}”);

}

Console.WriteLine(sb.ToString());

Whentheabovecodeiscompiledandexecuted,itproducesthefollowingresult:

In the example below we can select cars that have sold an odd number of units and order them alphabetically over its name:

varlist=fromcarincars

wherecar.UnitsSold%2!=0

orderbycar.Nameascending

selectcar;

Whentheabovecodeiscompiledandexecuted,itproducesthefollowingresult: