C# 4 and .NET 4

Updates ❘ 879
objeCTquery query builder meThods
OfType()
OrderBy()
Select() SelectValue()
Skip() Top()
Intersect() Union() UnionAll()
desCriPTion
This method specifies to return only those entities of a
specific type. This is very helpful with TPH relations.
This method is for defining the sort order of the entities.
These methods return a projection of the results. Select()
returns the result items in the form of a DbDataRecord;
SelectValue() returns the values as scalars or complex
types as defined by the generic parameter TResultType.
These methods are useful for paging. Skip a number of items
with the Skip() method and take a specified number as
defined by the Top() method.
These methods are used to combine two queries.
Intersect() returns a query containing only the results
that are available in both of the queries. Union() combines
the queries and returns the complete result without
duplicates. UnionAll() also includes duplicates.
Let’s get into one example on how to use these Query Builder methods. With the next code snippet, the
racers are filtered with the Where() method to return only racers from the USA; the OrderBy() method
specifies descending sort order first based on the number of wins and next on the number of starts. Finally,
only the first three racers are in the result using the Top() method:
This is the result from this query:
using (var data = new Formula1Entities())
{
string country = "USA";
ObjectQuery racers = data.Racers.Where("it.Country = @Country",
new ObjectParameter("Country", country))
.OrderBy("it.Wins DESC, it.Starts DESC")
.Top("3");
foreach (var racer in racers)
{
Console.WriteLine("{0} {1}, wins: {2}, starts: {3}",
racer.Firstname, racer.Lastname, racer.Wins, racer.Starts);
}
}
Mario Andretti, wins: 12, starts: 128
Dan Gurney, wins: 4, starts: 87
Phil Hill, wins: 3, starts: 48
code snippet Formula1Demo/Program.cs
uPdaTes
Reading, searching, and filtering data from the store are just one part of the work that usually needs to
be done with data-intensive applications. Writing changed data back to the store is the other part you
need to know.
The sections that follow cover these topics:
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Object tracking
Change information
Attaching and detaching entities
Storing entity changes
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