C# 4 and .NET 4

282 ❘ ChaPTer 11 lAnGuAGe inteGrAted Query
join
You can use the join clause to combine two sources based on specific criteria. But first, let’s get two lists
that should be joined. With Formula-1, there’s a drivers and a constructors championship. The drivers
are returned from the method GetChampions(), and the constructors are returned from the method
GetConstructorChampions(). Now it would be interesting to get a list by year where every year lists the
driver and the constructor champion.
For doing this, the first two queries for the racers and the teams are defined:
var racers = from r in Formula1.GetChampions()
from y in r.Years
where y > 2003
select new
{
Year = y,
Name = r.FirstName + " " + r.LastName
};
var teams = from t in
Formula1.GetContructorChampions()
from y in t.Years
where y > 2003
select new
{
Year = y,
Name = t.Name
};
Using these two queries, a join is done based on the year of the driver champion and the year of the team
champion with the clause join t in teams on r.Year equals t.Year. The select clause defines a
new anonymous type containing Year, Racer, and Team properties:
var racersAndTeams =
from r in racers
join t in teams on r.Year equals t.Year
select new
{
Year = r.Year,
Racer = r.Name,
Team = t.Name
};
Console.WriteLine("Year Champion " + "Constructor Title");
foreach (var item in racersAndTeams)
{
Console.WriteLine("{0}: {1,-20} {2}",
item.Year, item.Racer, item.Team);
}
Of course you can also combine this to one LINQ query, but that’s a matter of taste:
int year = 2003;
var racersAndTeams =
from r in
from r1 in Formula1.GetChampions()
from yr in r1.Years
where yr > year
select new
{
Year = yr,
Name = r1.FirstName + " " + r1.LastName
}
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