C# 4 and .NET 4

286 ❘ ChaPTer 11 lAnGuAGe inteGrAted Query
Jim Clark
Page 1
Juan Manuel Fangio
Nino Farina
Emerson Fittipaldi
Mika Hakkinen
Lewis Hamilton
Page 2
Mike Hawthorn
Phil Hill
Graham Hill
Damon Hill
Denny Hulme
Paging can be extremely useful with Windows or web applications showing the user only a part of the data.
An important behavior of this paging mechanism that you will notice: because the
query is done with every page, changing the underlying data affects the results. New
objects are shown as paging continues. Depending on your scenario this can be
advantageous to your application. If this behavior is not what you need, you can do
the paging not over the original data source, but by using a cache that maps to the
original data.
With the TakeWhile() and SkipWhile() extension methods you can also pass a predicate to take or skip
items based on the result of the predicate.
aggregate operators
The aggregate operators such as Count() , Sum() , Min() , Max() , Average() , and Aggregate() do not
return a sequence but a single value instead.
The Count() extension method returns the number of items in the collection. Here the Count() method is
applied to the Years property of a Racer to fi lter the racers and return only the ones who won more than
three championships:
The result is shown here:
var query = from r in Formula1.GetChampions()
where r.Years.Count() > 3
orderby r.Years.Count() descending
select new
{
Name = r.FirstName + " " + r.LastName,
TimesChampion = r.Years.Count()
};
foreach (var r in query)
{
Console.WriteLine("{0} {1}", r.Name, r.TimesChampion);
}
Michael Schumacher 7
Juan Manuel Fangio 5
Alain Prost 4
The Sum() method summarizes all numbers of a sequence and returns the result. Here, Sum() is used to
calculate the sum of all race wins for a country. First the racers are grouped based on the country, then with
the new anonymous type created, the Wins property is assigned to the sum of all wins from a single country:
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