###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 Data Structure

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 components (represented by the Component class) such as chains, wheels,
and frames, or finished products (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
part represents a tree of the parts that are used to build it. The lowest level of the tree consists
of components that do not contain other components.
A product is a part that has been completed and is ready to leave the factory. A product
typically consists of many components (forming a tree of child parts) but can also be
constructed by combining other products and/or components to form a bundled product, such
as a bicycle and a helmet that are sold together.
Components and products 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 details 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 Method.cs

Model.edmx

Model/Color.cs

Model/component.cs

Model ContosoEntities.cs

Model IName.cs

Model Part.cs

Model/Product.cs

SP_FindObsolete

###EndCaseStudy###

You have an existing ContosoEntities context object named context. Calling the SaveChanges()
method on the context object generates an exception that has the following inner exception:
System.Data.SqlClient.SqlException:
Cannot insert duplicate key row in object ‘dbo.Colors’ with unique index ‘IX_Colors’.

You need to ensure that a call to SaveChanges() on the context object does not generate this
exception. What should you do?

A.
Override the SaveChanges() method on the ContosoEntities class, call the
ObjectStateManager.GetObjectStateEntries(System.Data.EntityState.Added) method, and call the
AcceptChanges() method on each ObjectStateEntryobject it returns.

B.
Examine the code to see how Color objects are allocated. Replace any instances of the new Color()
method with a call to the ContosoEntities.LoadOrCreate() method.

C.
Add a try/catch statement around every call to the SaveChanges() method.

D.
Remove the unique constraint on the Name column in the Colors table.