###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 are adding a process to the application. The process performs the following actions:
1. Opens a ContosoEntities context object named context1.
2. Loads a Part object into a variable named part1.
3. Calls the Dispose() method on context1.
4. Updates the data in part1.
5. Updates the database by using a new ContosoEntities context object named context2.
You need to update the database with the changed data from part1.
What should you do?
A.
Add the following code segment before calling SaveChanges() on context2:
context2.Attach(part1) context2.ApplyCurrentValues(“Parts”, part1)
B.
Add the following code segment before calling SaveChanges() on context2:
context2.Attach(part1) context2.ObjectStateManager.ChangeObjectState(part1,
System.Data.EntityState.Modified)
C.
Add the following code segment before calling SaveChanges() on context2:
context2.ApplyCurrentValues(“Parts”, part1)
D.
Add the following code segment before calling SaveChanges() on context2:
context2.ApplyOriginalValues(“Parts”, part1)
Explanation:
How to: Apply Changes Made to a Detached Object
(http://msdn.microsoft.com/en-us/library/bb896248.aspx)
private static void ApplyItemUpdates(SalesOrderDetail originalItem, SalesOrderDetail updatedItem)
{
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
context.SalesOrderDetails.Attach(updatedItem);
// Check if the ID is 0, if it is the item is new.
// In this case we need to chage the state to Added.
if (updatedItem.SalesOrderDetailID == 0)
{
// Because the ID is generated by the database we do not need to
// set updatedItem.SalesOrderDetailID.context.ObjectStateManager.ChangeObjectState(updatedItem, System.Data.EntityState.Added);
}
else
{
// If the SalesOrderDetailID is not 0, then the item is not new
// and needs to be updated. Because we already added the
// updated object to the context we need to apply the original values.
// If we attached originalItem to the context
// we would need to apply the current values:
// context.ApplyCurrentValues(“SalesOrderDetails”, updatedItem);
// Applying current or original values, changes the state
// of the attached object to Modified.
context.ApplyOriginalValues(“SalesOrderDetails”, originalItem);
}
context.SaveChanges();
}}