Suresh
Kumar
Modern
software systems are component-based. Components make large,
enterprise-wide software systems easier to manage since system
functionality is divided among several components. VB.NET and all
other .NET-supported languages have the ability to create these
components, which can be used and reused in a variety of projects,
including (but not limited to) ASP.NET projects, Windows
applications, and unmanaged code (which is code that executes outside
the .NET Framework).
This
chapter covers the following topics:
Managed
code (the code that runs on the .NET Framework) and runtime
environments
The
Common Language Runtime and its role in the .NET Framework
Just-in-time
compilation of managed code
Code
assemblies
COM+
Component Services and its role in the .NET Framework
Creation
of managed components using VB.NET
Serviced
components, which take advantage of the services provided by COM+
Component Services
5.1 The
Concept of Managed Code Execution
Before
we get into making .NET components, we need to discuss a .NET concept
called managed code. Managed code is any source code you compile that
targets the .NET Framework. All the code we've examined so far in
this book (ASP.NET, console applications, and so on) has been managed
code.
The
.NET Framework is a runtime environment in which code executes.
Internal tasks, such as allocating and freeing memory, and software
services (like the kinds discussed in Chapter 4) are handled by the
.NET Framework as well. In general terms, a runtime environment
enables user programs to take advantage of services provided by the
host operating system. A runtime environment also supplies a layer of
abstraction between user code and those services, through either an
API or some other type of interface. Almost any program you write,
regardless of the platform or language, involves interaction with a
runtime environment. (An exception to this are programs written in
assembly language, in which case the programmer is calling on the
services of the microprocessor and memory storage in a direct,
low-level fashion.)
Many
programs written for the Windows platform use the C++ programming
language and its runtime library. Before other languages and
development systems became available, this was the only choice for
developers making applications for Windows. The C/C++ runtime code
shipped as a part of Windows as a series of dynamic link libraries
(known as DLLs or .dll files). As a result, many Windows applications
could be distributed with as little as one file, the .exe file that
contained the main program code. Since no other files were required,
many developers referred to these types of applications as native
code applications since the preinstalled runtime code was quite
small.
As
new languages became available for developing Windows applications,
new runtime environments needed to be developed. VB developers using
version 6.0 or earlier might be aware of special support files that
must be installed on the deployment computer in order for VB
applications to run. These .dll files make up the VB runtime
environment. Like the C/C++ runtime code mentioned above, it provides
a code wrapper around operating system internals and services.
Some
runtime environments provide an additional layer of abstraction over
another existing runtime environment. This creates an execution
environment that can exist on multiple platforms. Programs targeted
to such a runtime don't compile to machine object code. Instead, they
compile to another language, referred to as an intermediate language.
The runtime then executes this intermediate language using an engine
built for a particular operating system. The most popular type of
intermediate language system is Java. The intermediate language for
Java is referred to as bytecode. The .NET Framework works in a
similar manner. Compiled Microsoft .NET code is referred to as
Microsoft Intermediate Language (MSIL).
5.2
The Common Language Runtime
The
runtime environment for the .NET Framework is called the Common
Language Runtime (CLR). Managed code execution happens inside the CLR
space. The goal of the CLR is to provide an environment that includes
language integration, exception handling, security, versioning,
deployment, debugging, profiling, and component interaction. Most
importantly, all of these features need cross-language support. In
other words, all the features mentioned must work in the same manner
regardless of the language used.
Metadata
makes cross-language integration possible. When you compile .NET
managed code, the metadata gets stored along with the object code.
Metadata describes to the CLR various types of information (for
example, data types, members, and references) used in the code. This
data is used by the CLR to "manage" the code execution by
providing such services as memory allocation, method invocation, and
security enforcement. It also eases deployment since references to
other objects are included along with metadata. This ensures that
your application contains all up-to-date versions of all dependent
components.
5.2.1
The Common Type System
Along
with providing information about managed code through metadata, the
CLR implements a series of data types that are cross-language
compatible. That system of data types is known as the Common Type
System (CTS). CTS data types include simple value types, classes,
enumerated value types, interfaces, and delegates.
Simple
value data types include primitive types as well as user-defined
types. Primitive types include integers, Boolean values, and strings.
These types are included in the System namespace. The data types used
thus far in the VB.NET programs in this book are also included in
this namespace. When you use these primitive types in your programs,
the language you use may already have an equivalent native data type
that corresponds to a .NET Framework type. Table 5-1 shows some data
types and their VB.NET native language equivalents.
Table
5-1 Primitive Data Types and VB.NET Equivalents
NET | VB.NET |
Byte | Byte |
SByte | Not |
Int16 | Short |
Int32 | Integer |
Int64 | Long |
UInt16 | Not |
UInt32 | Not |
UInt64 | Not |
Single | Single |
Double | Double |
Object | Object |
Char | Char |
String | String |
Decimal | Decimal |
Boolean | Boolean |
Occasionally
you may want to define your own data types. You can do this by using
the native features of the language with which you're working. If
you're using VB.NET, you can use the Structure statement to define a
structure. This custom type needs to be type-safe for the CLR, so
it's no coincidence that it inherits from the ValueType .NET class.
techTalk:
structures and classes
Structures
and classes are quite similar. They both have members, constructors,
events, properties, fields, and constants. They can both implement
interfaces as well.
There
are some differences. Structures don't allow for inheritance;
therefore they are referred to as sealed.
Structures
can't have any constructor code, that is, you can't define an
overloaded New() subroutine with your own initialization code like
you can with a class.
When
structures are used in procedure calls, the structure is passed by
value (like primitive data types are). Classes, on the other hand,
are always passed by reference. Whether to use classes or structures
for your user-defined data types depends mostly on the complexity of
your data types. Structures are useful for defining relatively simple
data types for which the members do not use much memory and no custom
initialization code is required. If your design requires more than
this, consider defining your custom data type as a class.
Let's
quickly look at a VB.NET structure definition. Structure definitions
are placed outside of procedure definitions. You can define them at
the module level, as shown below.
Code
Sample 5-1 Build instructions: vbc /r:system.dll cs5-01.vb
Module
Module1
Structure Student
Dim
FirstName As String
Dim
LastName As String
Dim
SSN As String
Dim
ClassRank As Integer
End
Structure
Sub
Main()
Dim
udtStudent As New Student()
With udtStudent
.FirstName
= "Matt"
.LastName
= "Crouch"
.SSN
= "888-88-1234"
.ClassRank
= 2
End
With
End
Sub
End Module
The
example shows a typical structure definition. The members are
enclosed in the Structure...End Structure block that begins in line
The VB.NET With...End With statement in line 
used to save some typing. It allows you to refer to the individual
members of the structure without fully qualifying the names of the
structure members.
Since
the VB.NET structures you define automatically inherit from
System.ValueType, you can treat the value type as a ValueType object.
As a demonstration, let's create a function that lists all the
members of an arbitrary structure at runtime.
Code
Sample 5-2 Build instructions: vbc /r:system.dll cs5-02.vb
Public
Sub ValueTypeDemoFunction(ByVal udt As ValueType)
Dim
mi() As MemberInfo
Dim
srmMemberInfo As MemberInfo
Dim
typTmp As Type
typTmp =
udt.GetType(udt.ToString())
mi =
typTmp.GetMembers()
Console.WriteLine("Value
Type Information" & _
Chr(13)
& Chr(10))
For
Each srmMemberInfo In mi
Console.WriteLine(srmMemberInfo.Name)
Next
End Sub
The
function ValueTypeDemoFunction() takes a ValueType object as its
parameter. Thus we can pass a VB.NET structure to this function. The
GetType() function in line 
which is a member of the System.Object namespace, returns a
System.Type object. We use the returned System.Type object in line
get the member names (an array of System.Reflection.MemberInfo
objects).
If
we modify Code Sample 5-1 to add a call to ValueTypeDemoFunction() as
shown below in boldface text, we'll obtain output similar to Figure
5-1.
Sub
Main()
Dim
udtStudent As New Student()
With
udtStudent
.FirstName
= "Matt"
.LastName
= "Crouch"
.SSN
= "888-88-1234"
.ClassRank
= 2
End
With
ValueTypeDemoFunction(udtStudent)
End Sub
5.2.2
Just-in-Time Code Compilation
Managed
code cannot be executed directly by the CPU. It must be converted to
native executable code before running. Just-in-time (JIT) compilation
compiles MSIL code right at the moment it is needed. Optimizations
exist in the JIT compiler to ensure that only code planned for
execution gets compiled. The JIT compiler also performs security
checks and verifies type-safety.
5.2.3
Code Assemblies
I've
mentioned the topic of component-based system architectures before,
and now it's time to introduce the .NET Framework concept of this
idea. The component (that is, the unit of reuse) in the .NET
Framework is the assembly. An assembly is a collection of files,
typically .dll files and any others relating to the assembly, such as
resource files. The assembly manifest contains metadata relating to
version information, security attributes, and external code
references. It also contains information on how the pieces in the
assembly relate to each other. The assembly manifest, therefore,
constructs a logical DLL around the assembly elements.
5.2.4
Application Domains
Modern
software systems run applications that are isolated from the internal
execution of the operating system and other programs. The reason for
this is to protect the operating system from crashing if the
application attempts to access memory being used by another
application. Another situation that could cause a crash is an
internal error in the application that causes the operating system to
crash. Fortunately, all versions of Windows offer process protection
to prevent this problem. Each application running under Windows has
its own memory space, and memory used by other running applications
is not visible from any other application.
The
.NET Framework extends the capabilities of protected process spaces
by building this functionality into the CLR. These protected spaces
are known as application domains. In addition to the fault tolerance
that process isolation provides, application domains can enforce
security policies, thereby granting or denying users and groups the
right to run the application. Application domains also consume fewer
system resources than traditional Windows processes because they can
provide fault tolerance by taking advantage of the inherit
type-safety of the .NET Framework code.
5.3 COM+
Component Services
The
.NET Framework leverages many existing Windows services to make it a
more robust application environment. A particular technology that
deserves attention is COM+ Component Services. These technologies
were the predecessors to the .NET Framework. To see how COM+
Component Services fits into the .NET Framework arena, let's explore
a little about these technologies.
5.3.1
Overview of COM
The
Component Object Model (COM) was designed to address the shortcomings
of conventional object-oriented languages like C++ and traditional
binary software distribution of code. COM is about not a particular
type of software but rather a philosophy of programming. This
philosophy is manifested in the COM specification. The specification
explicitly states how a COM object should be constructed and what
behaviors it should have.
COM
objects are roughly equivalent to normal classes, but COM defines how
these objects interact with other programs at the binary level. By
binary, I mean compiled code, with all the methods and member
variables of the class already built into an object. This "binary
encapsulation" allows you to treat each COM object as a "black
box." You can call the black box and use its functionality
without any knowledge of the inner workings of the object's
implementation. In the Windows environment, these binary objects (COM
objects) are packaged as either DLLs or executable programs. COM is
also backed by a series of utility functions that provide routines
for instantiating COM objects, process communication, and so on.
COM
was the first methodology to address object-oriented software reuse.
COM has enjoyed great commercial success; many third-party software
vendors provide COM objects to perform a wide range of tasks, from
e-mail to image processing. COM is also highly useful for creating
components called business objects. Business objects are COM objects
in the strict sense, but they are used to encapsulate business rules
and logic. Typically these business objects are tied to database
tables. The objects move around the database according to the
business rules implemented in the COM object.
Generally,
several smaller business objects work together to accomplish a larger
task. To maintain system integrity and to prevent the introduction of
erroneous data into the application, transactions are used. A
software service called Microsoft Transaction Server (MTS) is used to
manage these transactions. We'll cover the function of MTS (and its
successor, COM+) in Section 5.3.3.
5.3.2
Overview of Transactions
Simply
stated, a transaction is a unit of work. Several smaller steps are
involved in a transaction. The success or failure of the transaction
depends on whether or not all of the smaller steps are completed
successfully. If a failure occurs at any point during a transaction,
you don't want any data changes made by previous steps to remain. In
effect, you want to initiate an "undo" command, similar to
what you would do when using, say, a word processor. A transaction is
committed when all steps have succeeded. A failed transaction causes
a rollback to occur (the "undo" operation).
Well-designed
transactions conform to ACID principles. ACID is an acronym for
Atomicity, Consistency, Isolation, and Durability.
Atomicity
means that either the operation that the component performs is
completely successful or the data that the component operates on
does not change at all. This is important because if the transaction
has to update multiple data items, you do not want to leave it with
erroneous values. If a failure occurs at any step that could
compromise the integrity of the system, the changes are undone.
Consistency
deals with preserving the system state in the case of a transaction
failure.
Isolation
means that a transaction acts as though it has complete control of
the system. In effect, this means that transactions are executed one
at a time. This process keeps the system state consistent; two
components executed at the same time that operate on the same data
can compromise the integrity of the system.
Durability
is the ability of a system to return to any state that was present
before the execution of a transaction. For example, if a hard drive
crash occurs in the middle of a transaction, you can restore the
original state from a transaction log stored on another disk to
which the system recorded.
A
classic example of a transaction operation is a bank transfer that
involves a transfer of funds from one account to another (a credit
and a debit). Such a transaction moves through the following steps.
Get
the amount to be transferred, and check the source account for
sufficient funds.
Deduct
the transfer amount from the source account.
Get
the balance of the destination account, and add the amount to be
transferred to the balance.
Update
the destination account with the new balance.
Suppose
a system failure occurs at step 4. The source account had the
transfer amount deducted but the amount was not added to the
destination account. Therefore, the money from the source account
gets lost. Clearly, this is not good because the integrity of the
database has been damaged.
Each
of the account transfer's steps can be checked for success or
failure. If a failure occurs before all values have been updated, the
program needs to undo the deduction made to the source account.
That's a rollback. If every step succeeds, the program needs to apply
all the changes made to the database. That's when a commit operation
is performed.
5.3.3
Automatic Transactions
Transactions
have been in widespread use since the early days of enterprise
computing. Many database systems include internal support for
transactions. Such database systems contain native commands to begin,
abort, and commit transactions. This way, several updates to database
data can be made as a group, and in the event of a failure, they can
be undone. Using a database's internal transaction-processing system
is referred to as manual transaction processing.
Automatic
transactions differ from manual transactions because automatic
transactions are controlled by a system external to the database
management system (DBMS). Earlier versions of Windows (95/98/NT)
provide automatic transaction services using Microsoft Transaction
Server (MTS). MTS works by coordinating database updates made by COM
components grouped into a logical unit called a package. An MTS
package defines the boundary of the transaction. Each component in
the package participates in the transaction. After a component
performs a piece of work (such as updating the database), it informs
MTS that it successfully (or unsuccessfully) performed its share of
the transaction. MTS then makes a determination to continue based on
the success of the last component's signal of success or failure. If
the transaction step was unsuccessful, the transaction is aborted
immediately, and MTS instructs the DBMS to undo any changes made to
data. If the step was successful, the transaction continues with the
other steps. If all steps execute successfully, MTS commits the
transaction and tells the DBMS to commit changes to the data.
5.3.4
COM+ Applications
With
the release of Windows 2000 came the next version of COM, dubbed
COM+. COM+'s raison d'être is the unification of COM and MTS.
COM+ also offers performance improvements over MTS by implementing
technologies such as object pooling, which maintains an active set of
COM component instances. Other performance-enhancing features include
load balancing, which distributes component instances over multiple
servers, and queued components, which uses Microsoft Message Queue
Server to handle requests for COM+ components.
The
services that were formerly provided by MTS are known as COM+
Component Services in the COM+ model. COM+ Component Services works
in a similar manner to MTS. Packages are now referred to as COM+
applications. Participating transactional components are grouped into
applications in the same way components were grouped into packages
under MTS.
Individual
COM+ components in an application can be assigned different levels of
involvement in an automatic transaction. When setting up COM+
applications, each component can have the levels of automatic
transaction support shown in Table 5-2.
Table
5-2 COM+ Automatic Transaction Support Levels
Transaction | Description |
Disabled | -No |
Not | -This |
Supported | -You |
Required | The |
Required | -The |
5.3.5
COM+ Security
Security
is of paramount importance, especially for applications intended to
run on the Internet. In the past, programming security features into
an Internet application was largely a manual effort. Often it
consisted of custom security schemes that did not necessarily
leverage the existing security infrastructure provided by the
operating system. Besides being difficult to maintain, such security
systems are typically costly to develop.
COM+
Component Services provides a security infrastructure for
applications that uses Windows 2000/XP users and groups. COM+
security is declarative, which means you designate which users and
groups have permission to access a COM+ application. This is done by
defining roles for application access.
A
role is a defined set of duties performed by particular individuals.
For example, a librarian can locate, check out, and shelve books. The
person fulfilling the librarian role is permitted to perform such
duties under the security policies defined for that role. An
administrator is responsible for assigning users and groups to roles.
The roles are then assigned to a COM+ application.
This
role-based security is not only easy to implement (it can be done by
the system administrator) but it also typically doesn't require the
programmer to work on the components to implement any security code.
When a call is made to a component running under COM+ Component
Services, COM+ checks the user/group identity of the caller and
compares it against the roles assigned to the component. Based on
that comparison, the call is allowed or rejected.
You
can provide additional security checking by using procedural
security. This type of security is implemented programmatically using
special .NET classes designed for interaction with COM+ Component
Services.
5.3.6
.NET Classes and COM+ Component Services
Thus
far, our discussions about COM+ Component Services, transactions, and
security deal specifically with COM+ components. COM+ predated the
.NET Framework and has had much success in enterprise-wide
applications developed using Microsoft Visual Studio 6.0. But how
does .NET fit into all of this?
COM+
still remains a dominant technology and is a significant part of
Windows. The architecture for .NET managed components was designed to
take advantage of all the features COM+ Component Services has to
offer (object pooling, transaction processing, security, and so on)
by providing classes to implement those features. These concepts are
very important when developing Web applications, too.
5.4 Using
VB.NET to Develop Managed Components
In
this section I'll present the concepts you need to understand to
build managed components using VB.NET.
5.4.1
Defining Namespaces
Namespaces
are a way to hierarchically organize class names. Namespaces become
especially useful when the number of classes available to you is
quite large. You've been exposed to namespaces quite a bit already in
this book. Whenever you write VB.NET code, you use .NET classes in
the System namespace. For example, when you use the
Console.WriteLine() command, you are using an assembly called Console
that exists in the System namespace. In the code, Console is not
fully qualified because it is assumed to be a part of the System
namespace based on the uniqueness of the name Console. You could
fully qualify the statement this way:
System.Console.WriteLine(...)
When
you create a new .NET assembly (program), a default root namespace is
assigned to the assembly. This name is typically the name of your
project. However, you are free to assign your own namespace names.
5.4.2
Using the Class Library
Managed
components start with a VS.NET project called a class library. The
class library puts the infrastructure in place for creating an
assembly for packing a component. Figure
5-2
shows the selections used to create a new class library project.
You
can specify several project properties and options for class library
projects. Of particular interest are the root namespace and the
assembly name. VB.NET creates default names for both of these
options. You can view and modify them by selecting the
Project'Properties menu. This opens the Property Pages dialog shown
in Figure
5-3.
By
default, VB.NET assigns the name you specified for the project as the
names for the assembly and the root namespace. You can override these
default names with better, more descriptive ones. Given these new
designations, references to classes inside the assembly would be made
in the following manner. (This example shows the usage of Dim to
declare an object for a particular class inside the assembly.)
Dim
objMyObject As objMyExample.SomeClassInTheAssembly
.NET
applications that you write need to include a reference to each
assembly you wish to use inside the main application. You can add a
reference to an assembly by right-clicking on the References folder
(see Figure
5-4)
and selecting Add Reference.... VS.NET displays a dialog with a list
of available assemblies (see Figure
5-5).
Those assemblies that are a part of the .NET Framework distribution
are displayed in the list. To add a reference to another assembly,
click the Browse... button. Then you'll be able to select the
assembly file you need.
Property Pages dialog
Add Reference dialog
5.4.3
Using Component "Plumbing" Code
When
class library projects are started in VB.NET, some stub code is
generated for you. A new, "empty" component's "plumbing"
code looks something like this:
Public
Class Class1
End
Class
The
VS.NET IDE adds this code for you for an empty class called Class1. A
.vb file is also generated that contains the class's code (which
VS.NET should be displaying in the front-most window). Give the class
another name (in the example below, we'll name it CTaxComponent) by
changing it in the editor and then renaming the class file in the
Solution Explorer to CTaxComponent. The code should now say:
Public
Class CTaxComponent
End
Class
5.4.4
Adding Initialization Code
Whenever
your component is instantiated, the New() subroutine is called. Any
initialization code you require goes here. As an illustration,
suppose your class contains a private member variable that you wish
to have an initial default value when the component is instantiated.
Such initialization code could look like the following.
Private
m_dblTaxRate As Double
Public
Sub New()
MyBase.New
'
Specify default percent tax rate
m_dblTaxRate
= 5
End
Sub
5.4.5
Creating Methods
In
Chapter 2 we discussed classes and several class concepts, such as
methods. When creating class libraries and components, you'll notice
that the same principles apply to components. Methods are simply
member functions and subroutines. In order for other .NET
applications to access methods you define, you need to expose them by
marking them for public access. Here's a public method definition and
implementation to illustrate.
Public
Function CalculatePriceAfterTax( _
ByVal
Amount As Double) As Double
CalculatePriceAfterTax
= Amount * (1 + (m_dblTaxRate / 100))
End
Function
5.4.6
Creating Properties
Component
properties are created in the same way as properties for regular
classes. Like methods, they should be marked for public access. The
property in the sample code below sets or gets the value of the
private class member variable used in the previous example.
Public
Property TaxRate() As Double
Get
TaxRate
= m_dblTaxRate
End
Get
Set(ByVal
Value As Double)
m_dblTaxRate
= Value
End
Set
End
Property
5.4.7
Using the Class Library in an Application
The
preceding sections described all the steps required to create a class
library that can function as an independent component in another
application. Now the class library needs to be tested. You can create
another .NET application that references the assembly and write code
to call the CTaxComponent class. The code below is a simple console
application that uses the class library.
Imports
System
Imports
SCDemoClasses
Imports
Microsoft.VisualBasic
Module
Module1
Sub
Main()
Dim
objTaxComponent As New CTaxComponent()
Dim
dblItemPrice As Double = 9.99
Dim
dblTotalPrice As Double
With
objTaxComponent
.TaxRate
= 7
dblTotalPrice
= _
.CalculatePriceAfterTax(dblItemPrice)
End
With
Console.WriteLine("{0}
after tax is {1}", _
FormatCurrency(dblItemPrice),
_
FormatCurrency(dblTotalPrice))
End
Sub
End
Module
This
code produces the following output (assuming U.S. currency):
$9.99
after tax is $10.69
WARNING
Before
this program can compile and run, a reference to the assembly DLL,
SCDemo (used in the example), must be added as a reference to the
hosting application (the sample console application) using the Add
Reference... command from the menu.
5-6
Database diagram of a supermarket ordering and inventory system
Table
5-3 Column Names and Data Types for the Inventory Table
Column | Data |
BinNumber | Varchar(255) |
SKU | Varchar(255) |
Quantity | Int |
Table
5-4 Column Names and Data Types for the Product Table
Column | Data |
SKU | Varchar(255) |
Description | Varchar(255) |
UnitPrice | Decimal |
StockingBinNumber | Varchar(255) |
Table
5-5 Column Names and Data Types for the Orders Table
Column | Data |
OrderNumber | Varchar(255) |
SupplierName | Varchar(255) |
OrderReceived | Bit |
Table
5-6 Column Names and Data Types for the OrderDetails Table
Column | Data |
OrderNumber | Varchar(255) |
LineItemNumber | Int |
SKU | Varchar(255) |
QuantityReceived | Int |
Quantity | Int |
ID | Identity |
TIP
Consult
your SQL Server documentation about creating a new database and
setting up tables if you are not familiar with the process. Recruit
the help of a database administrator if you need assistance in
obtaining authorization to create a database (if you're in an
enterprise/shared database environment). We will discuss database
access in detail in Chapter 7.
5.6 Building
VB.NET Serviced Components
Now
it's time for you to use serviced components to build the supermarket
ordering and inventory system outlined in the previous section!
You'll work through each step in the process, from designing to
coding and then testing the components in an ASP.NET application.
LAB 5-1
An Ordering and Inventory System Made with Serviced Components
STEP
1. Create a new VB.NET class library project.
Open
VS.NET and select File'New'Project.
Highlight
Class Library and give the new project the name "SupermarketSystem".
STEP
2. Design the components.
Consider
the design of your system. First, establish the users of the system
and their roles:
Supervisors
(adding new products, receiving orders, updating inventory)
Receiving
Clerks (receiving orders)
Suppliers
(shipping goods to the supermarket and supplying order information)
Organize
these functions into a series of classes for your class library.
Four classes will handle the business logic of the different duties
that each user will perform: Product, ReceiveOrder, UpdateInventory,
and CreateOrder. Lab
Figure 5-1
shows the classes and the methods of each class.
Figure 5-1
The classes and methods of the Supermarket program
Adding
a new product to the system, updating inventory, receiving an order,
and creating an order all involve operations on the database tier of
the application. For some of these operations, database updates can
occur in multiple tables. It's important to keep data integrity
across these tables. You also want to implement security features so
the users perform only the functions that their roles designate.
You'll see this functionality develop as you code the components.
STEP
3. Write code for component functionality.
In
the process of implementing the components, we'll discuss these
topics:
How
to use the System.EnterpriseServices namespace and one particular
class: the ServicedComponent class
How
to use class attributes to specify the type of COM+ support you want
your components to have
How
to specify an interface from which to call the components
How
to control the transaction inside the components
Create
the classes outlined in the specifications in Step 2: Product,
ReceiveOrder, UpdateInventory, and CreateOrder. For each of these
classes, right-click the project in the Solution Explorer and select
Add Class...from the menu. Name the classes as listed above. VS.NET
will "stub out" an empty class definition for each class.
Building
serviced components requires support from COM+ Component Services.
The .NET Framework implements this support through classes in the
System.EnterpriseServices namespace. VS.NET doesn't include this
reference by default, so you'll need to add it yourself. Select
Project'Add Reference from the menu and select
System.EnterpriseServices from the list. Click the Select button and
then click OK.
Now
you're ready to add component functionality. Start by adding the
following code for the Product class (Product.vb).
Lab
Code Sample 5-1
Imports
System
Imports
System.Reflection
Imports
System.EnterpriseServices
Imports
System.Data
Imports
System.Data.SqlClient
<Assembly:
ApplicationName("Supermarket")>
<Assembly:
ApplicationActivation(ActivationOption.Library)>
<Assembly:
AssemblyKeyFile("KeyFile.snk")>
Namespace
Supermarket
Public Interface
IProduct
Function
Create(ByVal SKU As String, _
ByVal
Description As String, _
ByVal
UnitPrice As Decimal, _
ByVal
StockingBinNumber As String) _
As
Boolean
End
Interface
<ConstructionEnabled(
_
[Default]:="Default
Construction String"), _
Transaction(TransactionOption.Required)>
_
Public
Class Product
Inherits
ServicedComponent
Implements
Supermarket.IProduct
Public
Sub New()
End
Sub
Protected
Overrides Sub Construct( _
ByVal
constructString As String)
End
Sub
Function
Create(ByVal SKU As String, _
ByVal
Description As String, _
ByVal
UnitPrice As Decimal, _
ByVal
StockingBinNumber As String) _
As
Boolean _
Implements
Supermarket.IProduct.Create
Dim
objCnn As SqlConnection
Dim
objCmd As SqlCommand
Dim
objParam As SqlParameter
Dim
intRowsReturned As Integer
Try
objCnn
= New SqlConnection()
objCnn.ConnectionString
= _
"Initial
Catalog=Supermarket;Data Source=localhost;uid=sa;pwd="
objCnn.Open()
objCmd
= objCnn.CreateCommand()
objCmd.CommandText
= _
"INSERT
INTO Product " & _
"(
SKU, Description, UnitPrice, StockingBinNumber ) " & _
"VALUES
( @sku, @description, @unitprice, @stockingbinnumber )"
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@sku"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= SKU
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@description"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= Description
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@unitprice"
.SqlDbType
= SqlDbType.Decimal
.Direction
= ParameterDirection.Input
.Value
= UnitPrice
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@stockingbinnumber"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= StockingBinNumber
End
With
objCmd.Parameters.Add(objParam)
intRowsReturned
= _
objCmd.ExecuteNonQuery()
Create
= True
ContextUtil.SetComplete()
Catch
E As Exception
Create
= False
ContextUtil.SetAbort()
Finally
objCnn.Close()
End
Try
End
Function
End
Class
End
Namespace
This
code implements a serviced component. As mentioned before, a serviced
component is a .NET class that uses COM+ Component Services. The
class becomes a serviced component when it derives from the
System.EnterpriseServices.ServicedComponent class. Before we talk
more about the ServicedComponent class, let's first investigate the
beginning of the code where some assembly-level attributes are
declared.
Making
a serviced component requires you to provide information to COM+
Component Services about the component's configuration. First you
designate to which package, or COM+ application, the component will
belong. That designation is made with the ApplicationName
assembly-level attribute shown in line 
The name for the order and inventory application is "Supermarket".
COM+ applications are listed in the Component Services Console.
COM+
Component Services provides a runtime environment for assembly
components. You can also control where the components are
activated—in the same process as the creator of the object
(IIS) or in a separate system process (dllhost.exe). You can control
application activation by specifying the ApplicationActivation
assembly attribute shown in line 
This code specifies ActivationOption.Library, which causes components
to be activated in the creator's process. So, if you were running
these components inside ASP.NET Web Forms, the creating process would
be the Web server, IIS. The ActivationOption.Server option provides
faster performance; this option, which runs the component in a system
process, provides more isolation, so the component's execution won't
adversely affect the execution of IIS. One advantage to using
ActivationOption.Library is to make debugging easier.
The
final assembly-level attribute, AssemblyKeyFile, specifies a shared
name for the assembly (see line 
The shared name is sometimes referred to as a strong name. A shared
name ensures that a name assigned to a component is unique. This is
accomplished by using a public/private cryptographic key pair to sign
each shared component in the assembly. The public key is then
published with the assembly. Besides specifying this attribute in the
code, you'll need to actually generate the key file specified for the
assembly-level attribute. To do this, use sn.exe, the Strong Name
Utility. Lab
Figure 5-2
shows how this is done.
Lab
Figure 5-2
Specifying a strong name for the assembly using sn.exe
The
usage of sn.exe, as shown in Lab
Figure 5-2,
outputs a .snk file. This is the file name that you specify in the
AssemblyKeyFile attribute in the code (change the path to the
location of your generated key file). You must complete this step
before you compile your project. These assembly-level attributes
appear once in the project's code. The class file in which they
appear is irrelevant, but they must be declared once and only once in
the assembly code.
Warning
Never
let anybody else have access to your .snk file. It contains a private
key that is for your use only.
Let's
move on to the main part of the component code. Line 
the Supermarket namespace, which will contain all the components for
the Supermarket application. Line 
an interface you'll use in the client application (the ASP.NET Web
Form) to call the component. The interface has one function,
Create(), which you'll use to set up a new product in the Product
database table.
The
component's class definition comes next. The code beginning in line
two class-level attributes for the Product class. The first one,
ConstructionEnabled, specifies that the class will be able to use
COM+ constructor strings. A constructor string is a string passed
into the activation procedure of the component. This string can be
specified by a system administrator inside the Component Services
Console. A constructor string can contain any information, but
typically you'll use it for passing initialization information to the
component. If no constructor string is given for the component in the
Component Services Console (see Lab
Figure 5-3,
which shows the Component Services Console dialog box for setting a
constructor string), a default constructor string is used by
specifying it in the attribute as shown in the continuation of line
The other class-level attribute specifies how the class will
participate in transactions. Use the Transaction attribute to specify
the participation level. In this code, Transaction uses
TransactionOption.Required. This indicates that the Product component
should participate in an existing transaction if one already exists.
If no transaction exists, a new transaction will begin and the
Product component will execute within the boundaries of that
transaction.
Lab
Figure 5-3
Specifying a constructor string in Component Services
The
class definition continues with the specification of an inherited
class and an Implements statement. Since this will be a serviced
component, it needs to derive from the ServicedComponent class, as
shown in line 
In line 
class implements the IProduct interface specified earlier.
Line
implementation support for constructor strings. Since the code
specified that the component will have support for constructor
strings with the class-level attribute ConstructionEnabled, here
there is an override method for the Construct() sub. This method will
be called upon object construction, and the constructor string
assigned to the component will be available in the constructString
variable.
Now
follows the implementation of the Create() method, which accepts a
new product's SKU number, product description, unit price, and
stocking bin number. The Create() method then executes the
appropriate ADO.NET code to insert a new row into the Product
database table. (ADO.NET code will be discussed in Chapter 7. For
now, just be aware that the Product component contains this method
that will be callable from an ASP.NET Web Form.)
Although
the discussion of the ADO.NET code details is deferred, it's
important to point out two details in the Create() method. These are
two methods of the ContextUtil object, SetComplete() in line 
SetAbort() in line 
These methods cast a vote in the current transaction. Typically, when
you have verified that all of the code inside a particular component
method has executed successfully, a call to SetComplete() is made.
This tells COM+ Component Services that a unit of work has succeeded
and that database integrity and consistency is assured for updates
made by the unit of work. It's a signal that the transaction can
continue running. Conversely, if a failure occurs (an exception or
other user-defined error or condition), the program needs to cast a
"fail" vote for the transaction by calling SetAbort(). This
will cause COM+ Component Services to stop the transaction and roll
back any changes made to the database by previous steps in the
transaction.
Now
that you understand the basic pieces of the Product class code, add
the code for the remaining classes (CreateOrder, UpdateInventory,
and ReceiveOrder). The implementations are all different, of course,
but they follow pretty much the same conventions as the Product
component.
Lab
Code Sample 5-2
Imports
System
Imports
System.Reflection
Imports
System.EnterpriseServices
Imports
System.Data
Imports
System.Data.SqlClient
Namespace
Supermarket
Public
Interface ICreateOrder
Function
Create(ByVal OrderNumber As String, _
ByVal
SupplierName As String) _
As
Boolean
Function
AddItems(ByVal OrderNumber As String, _
ByVal
SKU As String, _
ByVal
Quantity As Integer) _
As
Boolean
End
Interface
<ConstructionEnabled(
_
[Default]:="Default
Construction String"), _
Transaction(TransactionOption.Required)>
_
Public
Class CreateOrder
Inherits
ServicedComponent
Implements
ICreateOrder
Public
Sub New()
End
Sub
Public
Function Create(ByVal OrderNumber As String, _
ByVal
SupplierName As String) _
As
Boolean _
Implements
ICreateOrder.Create
Dim
objCnn As SqlConnection
Dim
objCmd As SqlCommand
Dim
objParam As SqlParameter
Dim
intRowsAffected As Integer
Try
objCnn
= New SqlConnection()
objCnn.ConnectionString
= _
"Initial
Catalog=Supermarket;Data Source=localhost;uid=sa;pwd="
objCnn.Open()
objCmd
= objCnn.CreateCommand()
objCmd.CommandText
= _
"INSERT
INTO Orders " & _
"(
OrderNumber, SupplierName, OrderReceived ) " & _
"VALUES
( @OrderNumber, @SupplierName, @OrderReceived )"
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@OrderNumber"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= OrderNumber
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@SupplierName"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= SupplierName
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@OrderReceived"
.SqlDbType
= SqlDbType.Bit
.Direction
= ParameterDirection.Input
.Value
= False
End
With
objCmd.Parameters.Add(objParam)
intRowsAffected
= objCmd.ExecuteNonQuery()
Create
= True
ContextUtil.SetComplete()
Catch
E As Exception
Create
= False
ContextUtil.SetAbort()
End
Try
End
Function
Public
Function AddItems(ByVal OrderNumber As String, _
ByVal
SKU As String, _
ByVal
Quantity As Integer) _
As
Boolean _
Implements
ICreateOrder.AddItems
Dim
objCnn As SqlConnection
Dim
objCmd As SqlCommand
Dim
objParam As SqlParameter
Dim
intMaxLineNumber As Integer
Dim
intRowsAffected As Integer
Dim
objTemp As Object
Try
objCnn
= New SqlConnection()
objCnn.ConnectionString
= _
"Initial
Catalog=Supermarket;Data Source=localhost;uid=sa;pwd="
objCnn.Open()
objCmd
= objCnn.CreateCommand()
objCmd.CommandText
= _
"SELECT
MAX( LineItemNumber ) " & _
"FROM
OrderDetails " & _
"WHERE
OrderNumber = @OrderNumber"
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@OrderNumber"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= OrderNumber
End
With
objCmd.Parameters.Add(objParam)
objTemp
= objCmd.ExecuteScalar()
If
TypeOf objTemp Is DBNull Then
intMaxLineNumber
= 1
Else
intMaxLineNumber
= CType(objTemp, Integer)
intMaxLineNumber
+= 1
End
If
objCmd
= objCnn.CreateCommand()
objCmd.CommandText
= _
"INSERT
INTO OrderDetails " & _
"(
OrderNumber, LineItemNumber, SKU, " & _
"QuantityReceived,
Quantity ) VALUES " & _
"(
@OrderNumber, @LineNumber, @SKU, " & _
"@QuantityReceived,
@Quantity )"
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@OrderNumber"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= OrderNumber
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@LineNumber"
.SqlDbType
= SqlDbType.Int
.Direction
= ParameterDirection.Input
.Value
= intMaxLineNumber
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@SKU"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= SKU
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@QuantityReceived"
.SqlDbType
= SqlDbType.Int
.Direction
= ParameterDirection.Input
.Value
= 0
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@Quantity"
.SqlDbType
= SqlDbType.Int
.Direction
= ParameterDirection.Input
.Value
= Quantity
End
With
objCmd.Parameters.Add(objParam)
intRowsAffected
= objCmd.ExecuteNonQuery()
AddItems
= True
ContextUtil.SetComplete()
Catch
E As Exception
AddItems
= False
ContextUtil.SetAbort()
Finally
objCnn.Close()
End
Try
End
Function
End
Class
End
Namespace
Lab
Code Sample 5-3
Imports
System
Imports
System.Reflection
Imports
System.EnterpriseServices
Imports
System.Data
Imports
System.Data.SqlClient
Namespace
Supermarket
Public
Interface IUpdateInventory
Function
Update(ByVal BinNumber As String, _
ByVal
SKU As String, _
ByVal
Quantity As Integer) _
As
Boolean
Function
GetStockingLocation(ByVal SKU As String) _
As
String
End
Interface
<ConstructionEnabled(
_
[Default]:="Default
Construction String"), _
Transaction(TransactionOption.Required)>
_
Public
Class UpdateInventory
Inherits
ServicedComponent
Implements
IUpdateInventory
Public
Sub New()
End
Sub
Public
Function GetStockingLocation( _
ByVal
SKU As String) As String _
Implements
IUpdateInventory.GetStockingLocation
Dim
objCnn As SqlConnection
Dim
objCmd As SqlCommand
Dim
objParam As SqlParameter
Dim
objTemp As Object
Try
objCnn
= New SqlConnection()
objCnn.ConnectionString
= _
"Initial
Catalog=Supermarket;Data Source=localhost;uid=sa;pwd="
objCnn.Open()
objCmd
= objCnn.CreateCommand()
objCmd.CommandText
= _
"SELECT
StockingBinNumber " & _
"FROM
Product WHERE SKU = @SKU"
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@SKU"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= SKU
End
With
objCmd.Parameters.Add(objParam)
objTemp
= objCmd.ExecuteScalar()
If
TypeOf objTemp Is DBNull Then
GetStockingLocation
= ""
Else
GetStockingLocation
= _
CType(objCmd.ExecuteScalar(),
String)
End
If
ContextUtil.SetComplete()
Catch
E As Exception
ContextUtil.SetAbort()
GetStockingLocation
= ""
Finally
objCnn.Close()
End
Try
End
Function
Private
Function InventoryRecExists( _
ByVal
SKU As String, _
ByVal
StockingBinNumber As String) _
As
Boolean
Dim
objCnn As SqlConnection
Dim
objCmd As SqlCommand
Dim
objParam As SqlParameter
Dim
intRowCount As Integer
Dim
objTemp As Object
Try
objCnn
= New SqlConnection()
objCnn.ConnectionString
= _
"Initial
Catalog=Supermarket;Data Source=localhost;uid=sa;pwd="
objCnn.Open()
objCmd
= objCnn.CreateCommand()
objCmd.CommandText
= _
"SELECT
COUNT(*) FROM Inventory " & _
"WHERE
SKU = @SKU AND " & _
"BinNumber
= @StockingBinNumber"
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@SKU"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= SKU
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@StockingBinNumber"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= StockingBinNumber
End
With
objCmd.Parameters.Add(objParam)
objTemp
= objCmd.ExecuteScalar()
If
TypeOf objTemp Is DBNull Then
intRowCount
= 0
Else
intRowCount
= CType(objTemp, Integer)
End
If
If
intRowCount > 0 Then
InventoryRecExists
= True
Else
InventoryRecExists
= False
End
If
ContextUtil.SetComplete()
Catch
E As Exception
InventoryRecExists
= False
ContextUtil.SetAbort()
Finally
objCnn.Close()
End
Try
End
Function
Private
Sub UpdateInventoryRecord( _
ByVal
BinNumber As String, _
ByVal
SKU As String, _
ByVal
Quantity As Integer)
Dim
objCnn As SqlConnection
Dim
objCmd As SqlCommand
Dim
objParam As SqlParameter
Dim
intRowCount As Integer
Try
objCnn
= New SqlConnection()
objCnn.ConnectionString
= _
"Initial
Catalog=Supermarket;Data Source=localhost;uid=sa;pwd="
objCnn.Open()
objCmd
= objCnn.CreateCommand()
objCmd.CommandText
= "UPDATE Inventory " & _
"SET
Quantity = Quantity + @Quantity " & _
"WHERE
BinNumber = @BinNumber AND SKU = @SKU"
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@Quantity"
.SqlDbType
= SqlDbType.Int
.Direction
= ParameterDirection.Input
.Value
= Quantity
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@BinNumber"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= BinNumber
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@SKU"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= SKU
End
With
objCmd.Parameters.Add(objParam)
intRowCount
= objCmd.ExecuteNonQuery()
ContextUtil.SetComplete()
Catch
E As Exception
ContextUtil.SetAbort()
Finally
objCnn.Close()
End
Try
End
Sub
Private
Sub InsertInventoryRecord( _
ByVal
BinNumber As String, _
ByVal
SKU As String, _
ByVal
Quantity As Integer)
Dim
objCnn As SqlConnection
Dim
objCmd As SqlCommand
Dim
objParam As SqlParameter
Dim
intRowCount As Integer
Try
objCnn
= New SqlConnection()
objCnn.ConnectionString
= _
"Initial
Catalog=Supermarket;Data Source=localhost;uid=sa;pwd="
objCnn.Open()
objCmd
= objCnn.CreateCommand()
objCmd.CommandText
= _
"INSERT
INTO Inventory " & _
"(
BinNumber, SKU, Quantity ) VALUES " & _
"(
@BinNumber, @SKU, @Quantity )"
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@BinNumber"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= BinNumber
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@SKU"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= SKU
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@Quantity"
.SqlDbType
= SqlDbType.Int
.Direction
= ParameterDirection.Input
.Value
= Quantity
End
With
objCmd.Parameters.Add(objParam)
intRowCount
= objCmd.ExecuteNonQuery()
ContextUtil.SetComplete()
Catch
E As Exception
ContextUtil.SetAbort()
Finally
objCnn.Close()
End
Try
End
Sub
Public
Function Update(ByVal BinNumber As String, _
ByVal
SKU As String, _
ByVal
Quantity As Integer) _
As
Boolean _
Implements
IUpdateInventory.Update
Dim
objCnn As SqlConnection
Dim
objCmd As SqlCommand
Dim
objParam As SqlParameter
Dim
strStockingLocation As String
Dim
intRowsAffected As Integer
Try
If
InventoryRecExists(SKU, BinNumber) Then
UpdateInventoryRecord(
_
BinNumber,
_
SKU,
_
Quantity)
Else
InsertInventoryRecord(
_
BinNumber,
_
SKU,
_
Quantity)
End
If
Update
= True
ContextUtil.SetComplete()
Catch
E As Exception
Update
= False
ContextUtil.SetAbort()
End
Try
End
Function
End
Class
End
Namespace
Lab
Code Sample 5-4
Imports
System
Imports
System.Reflection
Imports
System.EnterpriseServices
Imports
System.Data
Imports
System.Data.SqlClient
Namespace
Supermarket
Public
Interface IReceiveOrder
Function
GetNextLineItem(ByVal OrderNumber As String, _
ByRef
SKU As String) As Integer
Function
Receive(ByVal OrderNumber As String, _
ByVal
SKU As String, _
ByVal
LineNumber As Integer, _
ByVal
QuantityReceived As Integer) _
As
Boolean
End
Interface
<ConstructionEnabled(
_
[Default]:="Default
Construction String"), _
Transaction(TransactionOption.Required)>
_
Public
Class ReceiveOrder
Inherits
ServicedComponent
Implements
IReceiveOrder
Public
Sub New()
End
Sub
Private
Sub UpdateOrderDeatils( _
ByVal
OrderNumber As String, _
ByVal
LineNumber As Integer, _
ByVal
QuantityReceived As Integer)
Dim
objCnn As SqlConnection
Dim
objCmd As SqlCommand
Dim
objParam As SqlParameter
Dim
objSQLDr As SqlDataReader
Dim
intRowsAffected As Integer
Try
objCnn
= New SqlConnection()
objCnn.ConnectionString
= _
"Initial
Catalog=Supermarket;Data Source=localhost;uid=sa;pwd="
objCnn.Open()
objCmd
= objCnn.CreateCommand()
objCmd.CommandText
= _
"UPDATE
OrderDetails " & _
"SET
QuantityReceived = " & _
"QuantityReceived
+ @QuantityReceived " & _
"WHERE
OrderNumber = " & _
"@OrderNumber
AND LineItemNumber = @LineNumber"
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@QuantityReceived"
.SqlDbType
= SqlDbType.Int
.Direction
= ParameterDirection.Input
.Value
= QuantityReceived
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@OrderNumber"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= OrderNumber
End
With
objCmd.Parameters.Add(objParam)
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@LineNumber"
.SqlDbType
= SqlDbType.Int
.Direction
= ParameterDirection.Input
.Value
= LineNumber
End
With
objCmd.Parameters.Add(objParam)
intRowsAffected
= objCmd.ExecuteNonQuery()
ContextUtil.SetComplete()
Catch
E As Exception
ContextUtil.SetAbort()
Finally
objCnn.Close()
End
Try
End
Sub
Public
Function GetNextLineItem( _
ByVal
OrderNumber As String, _
ByRef
SKU As String) _
As
Integer Implements _
IReceiveOrder.GetNextLineItem
Dim
objCnn As SqlConnection
Dim
objCmd As SqlCommand
Dim
objParam As SqlParameter
Dim
objSQLDr As SqlDataReader
Try
objCnn
= New SqlConnection()
objCnn.ConnectionString
= _
"Initial
Catalog=Supermarket;Data Source=localhost;uid=sa;pwd="
objCnn.Open()
objCmd
= objCnn.CreateCommand()
objCmd.CommandText
= _
"SELECT
MAX(LineItemNumber), " & _
"SKU
FROM OrderDetails od, Orders o " & _
"WHERE
od.OrderNumber = @OrderNumber AND " & _
"o.OrderReceived
= 0 AND " & _
"o.OrderNumber
= od.OrderNumber GROUP BY SKU"
objParam
= New SqlParameter()
With
objParam
.ParameterName
= "@OrderNumber"
.SqlDbType
= SqlDbType.VarChar
.Direction
= ParameterDirection.Input
.Value
= OrderNumber
End
With
objCmd.Parameters.Add(objParam)
objSQLDr
= objCmd.ExecuteReader()
objSQLDr.Read()
If
Not objSQLDr.IsDBNull(0) Then
GetNextLineItem
= objSQLDr.GetInt32(0)
SKU
= objSQLDr.GetString(1)
Else
GetNextLineItem
= -1
SKU
= ""
End
If
ContextUtil.SetComplete()
objSQLDr.Close()
Catch
E As Exception
GetNextLineItem
= -1
SKU
= ""
ContextUtil.SetAbort()
Finally
objCnn.Close()
End
Try
End
Function
Public
Function Receive(ByVal OrderNumber As String, _
ByVal
SKU As String, _
ByVal
LineNumber As Integer, _
ByVal
QuantityReceived As Integer) _
As
Boolean _
Implements
IReceiveOrder.Receive
Dim
objCnn As SqlConnection
Dim
objCmd As SqlCommand
Dim
objParam As SqlParameter
Dim
objInvUpdate As IUpdateInventory
Dim
strBinNumber As String
Try
UpdateOrderDeatils(OrderNumber,
_
LineNumber,
_
QuantityReceived)
objInvUpdate
= New UpdateInventory()
strBinNumber
= _
objInvUpdate.GetStockingLocation(SKU)
If
objInvUpdate.Update(strBinNumber, _
SKU,
QuantityReceived) Then
Receive
= True
ContextUtil.SetComplete()
Else
Receive
= False
ContextUtil.SetAbort()
End
If
Catch
E As Exception
Receive
= False
ContextUtil.SetAbort()
End
Try
End
Function
End
Class
End
Namespace
Now
that you've entered the main code for the Supermarket COM+
application, it's time to compile it. Choose Build'Build Solution
from the menu to create the assembly file. In the next step, you'll
create a project that references that assembly.
STEP
4. Create the ASP.NET application.
Create
a new VB ASP.NET project called "SupermarketWeb".
Add
a reference to System.EnterpriseServices to the project by
right-clicking the project icon and selecting Add Reference... from
the pop-up menu.
Add
four new Web Forms (.aspx files) and their code-behind files (.vb
files) to the project, named as follows:
Lcs5-5.aspx,
Lcs5-5.aspx.vb
Lcs5-6.aspx,
Lcs5-6.aspx.vb
Lcs5-7.aspx,
Lcs5-7.aspx.vb
Lcs5-8.aspx,
Lcs5-8.aspx.vb
These
Web Forms will test the different components and their functionality.
Product
Component Test Web Form
The
HTML for the Lcs5-5.aspx file appears below.
Lab
Code Sample 5-5
<%@
Page Language="vb"
AutoEventWireup="false"
src="Lcs5-05.aspx.vb"
Inherits="WebForm1"
Transaction="RequiresNew"%>
<html>
<head>
<title>Create
New Product</title>
</head>
<body>
<form
id="Form1"
method="post"
runat="server">
<p>SKU:
<asp:TextBox
id=txtSKU
runat="server">
</asp:TextBox></p>
<p>Description:
<asp:TextBox
id=txtDescription
runat="server">
</asp:TextBox></p>
<p>Unit
Price:
<asp:TextBox
id=txtUnitPrice
runat="server">
</asp:TextBox></p>
<p>Stocking
Location:
<asp:TextBox
id=txtStockLoc
runat="server">
</asp:TextBox></p>
<p>
<asp:Button
id=cmdAddProduct
runat="server"
Text="Add
Product">
</asp:Button>
<asp:CompareValidator
id=CompareValidator1
runat="server"
ErrorMessage="You
must enter a price (number)"
Type="Double"
ControlToValidate="txtUnitPrice"
Operator="DataTypeCheck">
</asp:CompareValidator></p>
</form>
</body>
</html>
ASP.NET
Web Forms can run inside the context of a COM+ Component Services
transaction. In this ASP.NET Web application, the Web Forms call the
serviced components in response to events raised by Web Controls
(buttons clicked and so on). Since the ASP.NET Web Form is the
initiator of calls made into a COM+ application, the Web Form is
considered the root of the transaction. It has the "final vote"
as to whether or not the transaction succeeds or fails.
In
order to designate that the Web Form will participate in a
transaction, you need to set the Transaction page attribute
(highlighted in bold above). This code specifies the level as
RequiresNew. This means that the page will always begin a new
transaction for any units of work executed during the lifetime of the
page.
Here
is the code-behind file, Lcs5-5.aspx.vb, for the preceding Web Form.
Imports
SupermarketSystem.Supermarket
Imports
System.EnterpriseServices
Imports
System.Reflection
Imports
System.ComponentModel
Public
Class WebForm1
Inherits
System.Web.UI.Page
Protected
WithEvents cmdAddProduct As _
System.Web.UI.WebControls.Button
Protected
WithEvents txtSKU As _
System.Web.UI.WebControls.TextBox
Protected
WithEvents txtDescription As _
System.Web.UI.WebControls.TextBox
Protected
WithEvents txtUnitPrice As _
System.Web.UI.WebControls.TextBox
Protected
WithEvents txtStockLoc As _
System.Web.UI.WebControls.TextBox
Protected
WithEvents CompareValidator1 As_
System.Web.UI.WebControls.CompareValidator
Private
Sub Page_Load(ByVal sender As System.Object, _
ByVal
e As System.EventArgs) Handles MyBase.Load
End
Sub
Private
Sub cmdAddProduct_Click( _
ByVal
sender As System.Object, _
ByVal
e As System.EventArgs) _
Handles
cmdAddProduct.Click
Dim
objProduct As IProduct
Dim
bln As Boolean
objProduct
= New Product()
bln
= objProduct.Create(txtSKU.Text, _
txtDescription.Text,
_
CDec(txtUnitPrice.Text),
_
txtStockLoc.Text)
If
bln Then
ContextUtil.SetComplete()
Else
ContextUtil.SetAbort()
End
If
End
Sub
End
Class
The
Click event for the cmdAddProduct button calls the Product component
to add a new product to the database. The code creates a new Product
object and obtains a reference to the IProduct interface. It then
calls the Create() method. If the call was successful (returned
True), SetComplete() is called to indicate to COM+ that this unit of
work in the transaction was successful. If not, SetAbort()stops the
transaction immediately.
CreateOrder
Component Test Web Form
The
code for the Lcs5-6.aspx file follows below. Note that again the
Transaction page attribute is specified and set to RequiresNew.
Lab
Code Sample 5-6
<%@
Page Language="vb"
AutoEventWireup="false"
src="Lcs5-06.aspx.vb"
Inherits="SupermarketCreateOrder"
Transaction="RequiresNew"%>
<html>
<head>
<title>Create
New Order</title>
</head>
<body>
<form
id="Form1"
method="post"
runat="server">
<p>Order
number:
<asp:TextBox
id=txtOrderNumber
runat="server">
</asp:TextBox></p>
<p>Supplier
Name:
<asp:TextBox
id=txtSupplierName
runat="server">
</asp:TextBox></p>
<p>
<asp:Button
id=cmdCreateOrder
runat="server"
Text="Add">
</asp:Button></p>
</form>
</body>
</html>
The
code-behind file, Lcs5-6.aspx.vb, contains the following code.
Imports
System.EnterpriseServices
Imports
System.Reflection
Imports
SupermarketSystem.Supermarket
Public
Class SupermarketCreateOrder
Inherits
System.Web.UI.Page
Protected
WithEvents txtOrderNumber As _
System.Web.UI.WebControls.TextBox
Protected
WithEvents txtSupplierName As _
System.Web.UI.WebControls.TextBox
Protected
WithEvents cmdCreateOrder As _
System.Web.UI.WebControls.Button
Private
Sub Page_Load(ByVal sender As System.Object, _
ByVal
e As System.EventArgs) Handles MyBase.Load
End
Sub
Private
Sub cmdCreateOrder_Click( _
ByVal
sender As System.Object, _
ByVal
e As System.EventArgs) _
Handles
cmdCreateOrder.Click
Dim
objCreateOrder As ICreateOrder
objCreateOrder
= New CreateOrder()
If
objCreateOrder.Create(txtOrderNumber.Text, _
txtSupplierName.Text)
Then
ContextUtil.SetComplete()
Else
ContextUtil.SetAbort()
End
If
End
Sub
End
Class
Similar
to the test Web Form for the Product component, this code creates a
CreateOrder object using New. The program calls the Create() method
and then calls SetComplete() or SetAbort() upon success or failure,
respectively.
AddToOrder
Test Web Form
The
HTML code for the AddToOrder Web Form (Lcs5-7.aspx) appears below.
Lab
Code Sample 5-7
<%@
Page Language="vb"
AutoEventWireup="false"
Codebehind="SupermarketAddToOrder.aspx.vb"
Inherits="SupermarketWeb.SupermarketAddToOrder"
Transaction="RequiresNew"%>
<html>
<head>
<title>Add
To Order</title>
</head>
<body>
<form
id="Form1"
method="post"
runat="server">
<p>Order
Number:
<asp:TextBox
id=txtOrderNumber
runat="server">
</asp:TextBox></p>
<p>SKU:
<asp:TextBox
id=txtSKU
runat="server">
</asp:TextBox></p>
<p>Quantity:
<asp:TextBox
id=txtQuantity
runat="server">
</asp:TextBox></p>
<p>
<asp:CompareValidator
id=CompareValidator1
runat="server"
ErrorMessage="Quantity
must be a whole number!"
ControlToValidate="txtQuantity"
Type="Integer"
Operator="DataTypeCheck">
</asp:CompareValidator></p>
<p>
<asp:Button
id=cmdAddToOrder
runat="server"
Text="Add
To Order">
</asp:Button></p>
</form>
</body>
</html>
Here
is the associated code-behind file (Lcs5-7.aspx.vb). AddItems() is a
method of the CreateOrder component, so the code is very similar to
the CreateOrder Web Form.
Imports
System.EnterpriseServices
Imports
System.Reflection
Imports
SupermarketSystem.Supermarket
Public
Class SupermarketAddToOrder
Inherits
System.Web.UI.Page
Protected
WithEvents txtOrderNumber As _
System.Web.UI.WebControls.TextBox
Protected
WithEvents txtSKU As _
System.Web.UI.WebControls.TextBox
Protected
WithEvents txtQuantity As _
System.Web.UI.WebControls.TextBox
Protected
WithEvents CompareValidator1 As _
System.Web.UI.WebControls.CompareValidator
Protected
WithEvents cmdAddToOrder As _
System.Web.UI.WebControls.Button
Private
Sub Page_Load(ByVal sender As System.Object, _
ByVal
e As System.EventArgs) Handles MyBase.Load
End
Sub
Private
Sub cmdAddToOrder_Click( _
ByVal
sender As System.Object, _
ByVal
e As System.EventArgs) _
Handles
cmdAddToOrder.Click
Dim
objCreateOrder As ICreateOrder
objCreateOrder
= New CreateOrder()
If
objCreateOrder.AddItems(txtOrderNumber.Text, _
txtSKU.Text,
CInt(txtQuantity.Text)) Then
ContextUtil.SetComplete()
Else
ContextUtil.SetAbort()
End
If
End
Sub
End
Class
ReceiveOrder
Component Test Web Form
Finally,
here is the code (Lcs5-8.aspx) for the Web Form that will receive
items for an order.
Lab
Code Sample 5-8
<%@
Page Language="vb"
AutoEventWireup="false"
src="SupermarketReceiveOrder.aspx.vb"
Inherits="SupermarketReceiveOrder"
Transaction="RequiresNew"%>
<html>
<head>
<title>Receive
Order</title>
</head>
<body>
<form
id="Form1"
method="post"
runat="server">
<p>Order
Number to Receive:
<asp:TextBox
id=txtOrderToReceive
runat="server">
</asp:TextBox>
<asp:Button
id=cmdGetOrder
runat="server"
Text="Get
Order">
</asp:Button></p>
<p>
<asp:Panel
id=Panel1
runat="server"
Width="399px"
Height="144px"
Enabled="False">
<p>
<asp:Label
id=lblOrderNumber
runat="server"
Width="184px"
Height="19px">
</asp:Label></p>
<p></p><p>
<asp:Label
id=lblReceiveSKU
runat="server"
Width="183px"
Height="19px">
</asp:Label></p>
<p>
<asp:Label
id=lblLineNumberReceive
runat="server"
Width="188px"
Height="19px">
</asp:Label></p>
<p>
<asp:Label
id=Label1
runat="server"
Width="128px"
Height="19px">
Quantity
To Receive:
</asp:Label>
<asp:TextBox
id=txtQuantityToReceive
runat="server">
</asp:TextBox>
<asp:Button
id=cmdReceive
runat="server"
Text="Receive">
</asp:Button>
</asp:Panel></p>
</form>
</body>
</html>
This
Web Form wraps page elements in a Panel Web Control. The panel is
initially disabled to avoid displaying or enabling the order
information until a valid order number is keyed into the Web Form.
Here's the code-behind file (Lcs5-8.aspx.vb).
Imports
System.EnterpriseServices
Imports
System.Reflection
Imports
SupermarketSystem.Supermarket
Public
Class SupermarketReceiveOrder
Inherits
System.Web.UI.Page
Protected
WithEvents cmdGetOrder As _
System.Web.UI.WebControls.Button
Protected
WithEvents Panel1 As _
System.Web.UI.WebControls.Panel
Protected
WithEvents lblOrderNumber As _
System.Web.UI.WebControls.Label
Protected
WithEvents Label1 As _
System.Web.UI.WebControls.Label
Protected
WithEvents txtOrderToReceive As _
System.Web.UI.WebControls.TextBox
Protected
WithEvents cmdReceive As _
System.Web.UI.WebControls.Button
Protected
WithEvents lblReceiveSKU As _
System.Web.UI.WebControls.Label
Protected
WithEvents lblLineNumberReceive As _
System.Web.UI.WebControls.Label
Protected
WithEvents txtQuantityToReceive As _
System.Web.UI.WebControls.TextBox
Private
Sub Page_Load(ByVal sender As System.Object, _
ByVal
e As System.EventArgs) Handles MyBase.Load
End
Sub
Private
Sub cmdGetOrder_Click( _
ByVal
sender As System.Object, _
ByVal
e As System.EventArgs) _
Handles
cmdGetOrder.Click
Dim
objReceiveOrder As IReceiveOrder
Dim
intLineNumber As Integer
Dim
strSKUToReceive As String
objReceiveOrder
= New ReceiveOrder()
intLineNumber
= _
objReceiveOrder.GetNextLineItem(
_
txtOrderToReceive.Text,
_
strSKUToReceive)
If
intLineNumber <> -1 Then
ViewState("OrderToReceive")
= txtOrderToReceive.Text
ViewState("SKUToReceive")
= strSKUToReceive
ViewState("LineNumber")
= intLineNumber
Panel1.Enabled
= True
lblLineNumberReceive.Text
= _
"Line
Number: " & intLineNumber
lblOrderNumber.Text
= _
"Order
Number: " & txtOrderToReceive.Text
lblReceiveSKU.Text
= "SKU: " & strSKUToReceive
Else
Panel1.Enabled
= False
End
If
End
Sub
Private
Sub cmdReceive_Click( _
ByVal
sender As System.Object, _
ByVal
e As System.EventArgs) _
Handles
cmdReceive.Click
Dim
objReceiveOrder As IReceiveOrder
objReceiveOrder
= New ReceiveOrder()
If
objReceiveOrder.Receive( _
ViewState("OrderToReceive"),
_
ViewState("SKUToReceive"),
_
ViewState("LineNumber"),
_
CInt(txtQuantityToReceive.Text))
Then
ContextUtil.SetComplete()
Else
ContextUtil.SetAbort()
End
If
End
Sub
End
Class
This
form uses two Button Web Controls, cmdGetOrder and cmdReceive. This
makes a two-step process for receiving items for an order. First, the
event handler for cmdGetOrder calls GetNextLineItem(), taking as
input the order number the user entered. If there is a line item to
receive for the order, the program displays the line-item information
in the Label Web Control contained within the Panel Web Control. The
Panel Web Control is then enabled, making the information visible to
the user. The line-item information is also copied to the ViewState
StateBag because the program will need this information on the
subsequent post-back that will occur when items are received.
The
event handler for cmdReceive calls the Receive() method. The
Receive() method updates the OrderDetails table as well as the
Inventory table. Using a transaction in this situation helps point
out any discrepancies between quantities in inventory and quantities
ordered. The Receive() method returns True on success and False on
failure, and the program makes an appropriate call to either
SetComplete() or SetAbort() as a result.
Now
you need to add a reference to the assembly DLL for the components.
Right-click the References folder in the Solution Explorer, select
Add Reference, browse to the compiled DLL, and select it. Click OK
to add the reference to the selected assembly.
STEP
5. Run the application.
Now
you're ready to build the application. Select Build'Build Solution
from the menu. Select a start page for the application (like
Lcs5-5.aspx) by right-clicking on a Web Form in the Solution
Explorer and selecting Set As Start Page from the menu.
Run
the application by selecting Debug'Start Without Debugging.
Test
the application by entering some products. Then create a new order,
add some items to the order, and run an order-receive process. This
should complete a full test.
Something
important happened when you first called a component's method inside
the assembly. The system performed what is known as a lazy
registration. A lazy registration automatically places the components
in the assembly into a new COM+ application in the COM+ Component
Services Console. It does this based on the assembly-level attributes
specified in the component assembly code. Lab
Figure 5–4
shows the Supermarket COM+ application in the COM+ Component Services
Console.
5-4
The Supermarket application within the COM+ Component Services
Console
STEP
6. Add role-based security.
One
of the requirements for the application is that only certain
categories of users should be allowed to run certain components. To
enable role-based security for the Supermarket COM+ application,
right-click on the Supermarket COM+ application icon and select
Properties. Click the Security tab. Check the boxes and radio
buttons as shown in Lab
Figure 5-5.
Figure
5-5
Enabling role-based security for the Supermarket application
Now
you can set up the user roles (Receiving Clerks, Supervisors, and
Suppliers) inside the COM+ Component Services Console. For each
role, right-click the Roles folder under the Supermarket application
(see Lab Figure
5-6),
select New'Role from the menu, and assign a name for the role.
Figure
5-6
Adding roles for the Supermarket application
Assign
users to each role by right-clicking the User folder under the role
and selecting New'User from the menu. Pick a Windows account name(s)
or group(s) to assign to the role. Lab
Figure 5-7
shows users assigned to the various roles of the Supermarket
application.
Now
you need to assign each role to a component. Right-click a component
in the COM+ application and select Properties from the menu. Click
the Security tab. Check Enforce component level access checks, and
then check the roles you wish to assign to the component, as shown
in Lab
Figure 5-8.
Figure
5-8
Assigning roles to components
STEP
7. Test the role-based security.
A
convenient way to test the role-based security is to call the
components from a console application and run the console
application in the security context of a specific user. Normally,
when you run an application from the console, Windows uses the
security context of the currently logged-on user. By using the runas
command, you can run an executable program using any account name
(provided, of course, you have the password of that account!).
Here's a simple console application you can run to test role-based
security.
Imports
System
Imports
SupermarketSystem.Supermarket
Imports
System.EnterpriseServices
Module
Module1
Sub
Main()
Dim
objCreateOrder As ICreateOrder
objCreateOrder
= New CreateOrder()
objCreateOrder.Create("834957239-1",
"My Supplier")
End
Sub
End
Module
Compile
this small testing console application and run it using the runas
command below:
runas
/user:rmdevbiz01\matt roletester.exe
Given
the role configuration of the CreateOrder component, the username
"matt" should be the only user allowed to run the
application. Assuming that the user account "matt" has
appropriate Windows permissions set to run the program, it should
execute without errors.
You
can also perform a negative test by rerunning the program with an
account name not included in the Supplier role.
5.7 Summary
Let's
recap what you've learned in this chapter about writing .NET managed
components.
Managed
code is application code that executes within the .NET Framework.
Runtime
systems enable application programs you write to access operating
system–level services. Several different runtime environments
are available for various systems. A runtime environment is usually
specific to a programming language.
Intermediate
languages provide an additional layer of abstraction over another
existing runtime environment. The goal of intermediate languages is
to provide portability of application code across operating systems.
The intermediate language for the .NET Framework is called the
Microsoft Intermediate Language (MSIL).
The
runtime environment for the .NET Framework is called the Common
Language Runtime (CLR). It supports self-describing code through
metadata, a specification for the Common Type System (CTS),
just-in-time compilation of code, and the concept of assembly
manifests, which describe a packaged set of components, programs,
files, and other dependencies an application needs in order to
function properly.
COM
is a programming model invented by Microsoft that allows for
binary-level software component reuse.
Transactions
provide consistency and data integrity to a software system. By
checking the success or failure of smaller atomic tasks that make up
the transaction, you can decide whether the transaction should
succeed as a whole.
Windows
provides programmers with easy transaction support for their
applications through COM+ Component Services. COM+ Component
Services provides transaction support, object pooling, and
component-level runtime security.
Components
are simply classes at their most basic level. Components have
properties and methods, which roughly correspond to member functions
and member variables, respectively.
Serviced
components are classes that take advantage of COM+ Component
Services. Security is provided by grouping users into roles and
assigning those roles to components.
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