###BeginCaseStudy###
Case Study: 1
Background
You are updating an existing Microsoft .NET Framework 4 application that includes a data
layer built with ADO.NET Entity Framework 4. The application communicates with a

Microsoft SQL Server 2008 instance named INST01 on a server named SQL01. The
application stores data in a database named Contoso in the INST01 instance.
You need to update the existing technology and develop new functionality by using
Microsoft Visual Studio 2010.
Application and Database Storage
The application tracks bicycle parts as they pass through a factory. Parts are represented by
the abstract Part entity and its associated partial classes. Each part has a name stored in the
Name field and a unique identifier stored in the Id field.
Parts are either component s (represented by the Component class) such as chains, wheels,
and frames, or finished product s (represented by the Product class) such as completed
bicycles. The Component class and the Product class derive from the Part class and may
contain additional class-specific properties.
Parts may have a color (represented by the Color class), but not all parts have a color, Parts
may be composed of other parts, and those parts may in turn be composed of other parts ; any
p art represents a tree of the parts that are used to build it, The lowest level of the tree consists
of c omponents that do not contain other component s.
A p roduct is a p art that has been completed and is ready to leave the factory. A p roduct
typically consists of many c omponents (forming a tree of child p arts) but can also be
constructed by combining other p roducts and/or c omponents to form a bundled p roduct,
such as a bicycle and a helmet that are sold together.
C omponents and p roducts are stored in a database table named Parts by using a table-perhierarchy (TPH) mapping. Components have a null ProductType field and a non-null
PartType field. Products have a non-null ProductType field and a null PartType field.
The following diagram illustrates the complete Entity data model diagram (EDMX diagram),

The following graphic illustrates detail s of the Part-Color Association.

The following code segments show relevant portions of the files referenced by the case study
items. (Line numbers in the samples below are included for reference only and include a twocharacter prefix that denotes the specific file to which they belong.)
Extension Methods.vb

Model.edmx

Model/Color.vb

Model/Component.vb

ModelContosoEntities.vb

Model IName.vb

Model Part.vb

Model Product.vb

sp_FindObsolete

###EndCaseStudy###

You have a ContosoEntities context object named context and a Color object stored in a variable
named color.
You write the following code:
context.Colors.DeleteObject(color)
context.SaveChanges()
When the code runs, it generates the following exception:
System.Data.UpdateException:
An error occurred while updating the entries. See the inner exception for details. —>
System.Data.SqlClient.SqlException: The DELETE statement conflicted with the REFERENCE
constraint “FK_PartColor”. The conflict occurred in database “Contoso”, table “dbo.Parts”, column
‘ColorId’.
You need to resolve the exception without negatively impacting the rest of the application.
What should you do?

A.
Add code before the call to the DeleteObject() method to examine the collection of Part objects
associated with the Color object and then assign null to the Color property for each Part object.

B.
Change the End1 OnDelete property of the FK_PartColor association from None to Cascade.

C.
In the database, remove the foreign key association between the Parts table and the Colors table,
and then update the entity data model.

D.
Add a transaction around the call to the SaveChanges() method and handle the exception by
performing a retry.

E.
Change the End2 OnDelete property of the FK_PartColor association from None to Cascade.