C# 4 and .NET 4

884 ❘ ChaPTer 31 AdO.net entity frAmewOrk
}
foreach (Racer r in racers)
{
Console.WriteLine("{0} {1}", r.Firstname, r.Lastname);
}
code snippet Formula1Demo/Program.cs
This is the result of accessing the Formula1 database:
Michael Schumacher
Alain Prost
Ayrton Senna
You can also define a LINQ query to access relations as shown here. Variable r references racers, variable
rr references all race results. The filter is defined with the where clause to retrieve only racers from
Switzerland who had a race position on the podium. To get the podium finishes, the result is grouped, and
the podium count calculated. Sorting is done based on the podium finishes:
using (var data = new Formula1Entities())
{
var query = from r in data.Racers
from rr in r.RaceResults
where rr.Position = 1 &&
r.Country == "Switzerland"
group r by r.Id into g
let podium = g.Count()
orderby podium descending
select new
{
Racer = g.FirstOrDefault(),
Podiums = podium
};
foreach (var r in query)
{
Console.WriteLine("{0} {1} {2}", r.Racer.Firstname, r.Racer.Lastname,
r.Podiums);
}
}
The names of three racers from Switzerland are returned when you run the application:
Clay Regazzoni 28
Jo Siffert 6
Rudi Fischer 2
summary
In this chapter, you’ve seen the features of the ADO.NET Entity Framework. The ADO.NET Entity
Framework is based on mapping that is defined by CSDL, MSL, and SSDL — XML information that
describes the entities, the mapping, and the database schema. Using this mapping technique, you can create
different relation types to map entity classes to database tables.
You’ve seen how the object context keeps knowledge about entities retrieved and updated, and how the
changes can be written to the store.
LINQ to Entities is just a facet of the ADO.NET Entity Framework that allows you to use the new query
syntax to access entities.
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