C# 4 and .NET 4

object Context ❘ 871
Class or inTerfaCe
IEntityWithKey
desCriPTion
This interface defi nes an EntityKey property that allows fast access to
the object.
IEntityWithChangeTracker This interface defi nes the method SetChangeTracker() where a change
tracker that implements the interface IChangeTracker can be assigned to
get information about state change from the object.
IEntityWithRelationships This interface defi nes the read-only property RelationshipManager,
which returns a RelationshipManager object that can be used to navigate
between objects.
For an entity class, it ’ s not necessary to derive from the base classes EntityObject or
ComplexObject . Instead, an entity class can implement the required interfaces.
The Book entity class can easily be accessed by using the object context class BooksEntities . The Books
property returns a collection of Book objects that can be iterated:
using (var data = new BooksEntities())
{
foreach (var book in data.Books)
{
Console.WriteLine("{0}, {1}", book.Title, book.Publisher);
}
}
code snippet BooksDemo/Program.cs
objeCT ConTeXT
To retrieve data from the database, the ObjectContext class is needed. This class defi nes the mapping from
the entity objects to the database. With core ADO.NET, you can compare this class to the data adapter that
fi l l s a DataSet .
The BooksEntities class created by the designer derives from the base class ObjectContext . This class
adds constructors to pass a connection string. With the default constructor, the connection string is read
from the confi guration fi le. It is also possible to pass an already opened connection to the constructor in the
form of an EntityConnection instance. If you pass a connection to the constructor that is not opened,
the object context opens and closes the connection; if you pass an opened connection you also need to close it.
The created class defi nes Books and Authors properties, which return an ObjectSet < TEntity > .
ObjectSet < TEntity > that is new with .NET 4 and derives from ObjectQuery < TEntity > :
public partial class BooksEntities : ObjectContext
{
public BooksEntities() : base("name=BooksEntities", "BooksEntities")
{
this.ContextOptions.LazyLoadingEnabled = true;
OnContextCreated();
}
public BooksEntities(string connectionString) : base(connectionString, "BooksEntities")
{
this.ContextOptions.LazyLoadingEnabled = true;
OnContextCreated();
}
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