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N-Tier Applications And .NET

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Introduction

Creating N-tier applications is not a new concept now. Since VB4 days Developers are building such applications. .NET provides great support for building such applications. This article is intended to give you an overview of n-tier architecture as applicable to .NET and how various technology choices offered by .NET fit in the picture.

What is N-Tier Application?

In n-tier architecture the entire application is divided in several pieces. These pieces can be logical or physical. Each piece performs a specific task such as displaying user interface or data access. There can be any number of tiers or layers of such pieces. Hence, the name n-tier (Note that many times the terms tier and layer are used interchangeably). However, most commonly applications have 3 distinct tiers or layers. They are:

  • Presentation Layer
  • Business Logic Layer
  • Data Access Layer

As you can guess, presentation layer is nothing but a piece of software that deals with user interface of your application. Displaying data to the end user and allow them to interface with it is the core functionality of this layer.

In most of the cases the data entered by the end user needs some kind of validation or further processing. This is the responsibility of Business Logic Layer.

Finally, your application data needs to be stored and retrieved in some data store (RDBMS, XML etc.). This task is handled by Data Access Layer.

In short, the process works like this:

  • User requests for some application data.
  • The data access layer retrieves the data and is forwarded to the presentation layer via business logic layer. Sometimes data access layer gives this data directly to presentation layer.
  • Presentation layer receives the data to be displayed via business logic layer.
  • The user changes the data and initiates the appropriate action (such as insert, or update).
  • The business logic layer validates the data submitted by the user.
  • If the data is valid it is handed over to data access layer for updating into the database.

Advantages of N-Tier Architecture

At first glance this division of tasks may seem to be unnecessary. However, it gives following benefits:

  • The applications gets divided in logically isolated pieces reducing tight coupling between the UI, business processes and database.
  • Change in the underlying database and data access methods do not have any effect on the presentation layer or client application.
  • Client application no longer has SQL statements embedded in it. This makes it de-coupled from rest of the application.
  • Table and column names can be effectively eliminated from the client-side code.
  • The client application is unaware from where data comes (location transparency).
  • It becomes easier to modify or extend your application, without breaking or recompiling the client-side code.

The downside of n-tier architecture is that you need to create many isolated classes and pieces of software. However, benefits of n-tier applications will far outweigh its disadvantage.

Presentation layer options

There are two main options for creating presentation layers in .NET. They are - Windows Forms or ASP.NET Web Forms.

Using windows forms you can create traditional forms based desktop applications. Windows forms applications can offer rich user interface elements and response times to the user. However, they suffer from the drawback that they need to be installed on each and every machine. Though they can be used in "smart client" mode they are more or less the same as traditional VB forms.

The most appealing option to develop presentation layer is ASP.NET web forms. Traditionally web pages suffered from the drawback of limited user interface elements. ASP.NET web server controls bridge the gap to a great extent. Controls such as DataGrid, DataList and Calendar provide rich UI in very few lines of code.

Above presentation layer options can be coded in variety of languages such as C# or VB.NET. Here, again support for multiple development languages comes handy. You can use your choice of language to develop the UI.

Business logic layer options

Business logic layer primarily consists of components that perform the task of business validation, business workflow and other similar things.

.NET components form this layer. In case you have invested a lot in COM components then you can also use them in .NET via interop. However, this will degrade the performance.

ASP.NET Web Service can also serve as business logic layer. However, they should not be used as replacement to components in all the situations. They should be used only if the business validation happens at some "external" place than your network.

The components you develop need not always reside on the same machine. Using .NET Remoting you can create distribute them on multiple physical machines.

Data access layer options

This layer deals with data manipulation actions such as inserts, updates, deletes and selects. The data mentioned above can reside in RDBMS or XML files or even flat files. You should design data access layer in such a way that other layers need not have any knowledge about underlying data store.

ADO.NET is the data access technology under .NET. Though ADO.NET allows connected data access via DataReader classes more focus is on disconnected data access. DataSet plays a key in this mode. In some rare cases you can also use ADO for data access but it's use should have valid reasons. Do not use ADO just because you like Recordset!

Again .NET components form this layer. As stated earlier you may also use classic COM components.

Web services can also form data access layer. This is especially true if your database do not have a data provider. In such cases you can write some custom code to connect with the data and populate DataSet with it and then return DataSet to the caller.

In addition to ADO.NET you can also make use of built-in RDBMS capabilities such as stored procedures and functions.

Passing data from one layer to another

Passing data from one layer to another is required in almost all the cases. Traditionally developers used comma separated strings, arrays and disconnected recordsets to achieve this. In .NET, DataSet provides an excellent way to pass your data across layers. You can even create the DataSet programmatically and populate it with your data. If you like objects a lot then you can make use of "Typed DataSets". Typed DataSet is nothing but a class derived from DataSet that exposes the tables and rows as objects.

The overall picture

Following figure shows how all these parts fit in:

image

posted Nov 29, 2016 by Shivaranjini

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Introduction

Since their introduction ASP.NET application services are popular and widely adopted means to implement membership, profile and role based security in web applications. Starting from .NET framework 3.5, Windows applications can also avail these features under the banner of Client Application Services. In this article I will show you how these services can be consumed in Windows Forms applications.

When to use Client Application Services?

Client application services allow you to do the following tasks:

  • Authenticate users
  • Implement role based security
  • Read and write Web settings (Profile) for a user

Client application services can be used in the following situations:

  • When you wish to share the same user credentials between web and windows applications
  • While developing a smart client application
  • When part of the system is web based and part of it is Windows based

It should be noted, however, that client application services are not standalone equivalent of application services for Windows applications. They are designed to allow Windows application share the same set of users that a web site is using.

Namespaces involved

The System.Web.Extensions assembly provides two namespaces related to client application services:

  • System.Web.ClientServices
  • System.Web.ClientServices.Providers

The former namespace contains classes that provide support to the ASP.NET application services. The later namespace contains classes related to client service providers.

Implementation steps

In order to make use of the client application services you need to take the following steps:

  • Configure database to support application services
  • Create a web site application
  • Configure membership, role and profile providers
  • Expose ASP.NET application services to Windows applications
  • Create a Windows Forms application
  • Enable client application services in the Windows Forms application
  • Retrieve profile properties in the Windows Forms application
  • Consume client application services

Let's develop a simple example that implements all the above steps.

Configure database to support application services

In order to configure a database to support ASP.NET application services you need to run aspnet_regsql.exe command line tool. If you ever used application services before you should be familiar with this command. Running this tool starts a wizard that guides you to further steps. The following figure shows the initial wizard step.

image

This tool creates several tables and stored procedures in the specified database that are used by ASP.NET application services.

Create a web site application

Now create a new web site using Visual Studio. In real world scenario this will be a functional web site. Since our intention is to illustrate the user of client application services we will not develop any web form in the web site. You can safely delete all the web forms from this web site. You nevertheless need to create the web site because it is this web site that expose the ASP.NET application services to Windows Forms application.

Configure membership, role and profile providers

The next step is to enable Forms authentication and configure membership, role and profile providers. Open web.config of the web site you just created and add the following markup to it.

<authentication mode="Forms"/>

<membership defaultProvider="p1">
<providers>
<add name="p1" connectionStringName="connstr" 
type="System.Web.Security.SqlMembershipProvider"/>
</providers>
</membership>

<roleManager enabled="true" defaultProvider="p2">
<providers>
<add name="p2" connectionStringName="connstr" 
type="System.Web.Security.SqlRoleProvider"/>
</providers>
</roleManager>

<profile enabled="true" defaultProvider="p3">
<providers>
<add name="p3" connectionStringName="connstr" 
type="System.Web.Profile.SqlProfileProvider"/>
</providers>
<properties>
<add name="FullName" type="string" 
readOnly="false" defaultValue="abcd" 
serializeAs="String" allowAnonymous="false"/>
</properties>
</profile>

Here, we first enabled Forms authentication for the web site. Then we configure membership, role and profile providers using <membership>, <roleManager> and <profile> tags. Make sure that the connection string connstr points to your database that you configured for application services. Notice that the above markup defines one profile property named FullName that is of type string.

Expose ASP.NET application services to Windows applications

Now comes the important step. In order that Windows applications can consume ASP.NET application services you must expose them from your web site. This is done by adding <system.web.extensions> section inside <configuration> root element.

<system.web.extensions>
<scripting>
<webServices>
<authenticationService 
enabled="true" requireSSL="false"/>
<roleService enabled="true"/>
<profileService enabled="true" 
readAccessProperties="FullName" 
writeAccessProperties="FullName"/>
</webServices>
</scripting>
</system.web.extensions>

Notice the markup shown in bold letters. The <authenticationService>, <roleService> and <profileService> tags expose membership, role and profile services to the external world.

If you worked in ASP.NET AJAX you should be familiar with this markup as AJAX consumes the same services from client side script.

Observe the <profileService> markup carefully. The readAccessProperties and writeAccessProperties attributes govern which profile properties can be read and write respectively.

In real world cases you will be deploying this web site to a known URL. For the sake of testing however we need to tell Visual Studio the port number to use for running this web site. This is done in the web site property pages as shown below:

image

Make sure to specify a specific port (5555 in the above figure) and a virtual path (/ClientAppServHost). This way at runtime the URL of our web site will be http://localhost:5555/ClientAppServHost.

Create a Windows Forms application

The next step is to add a new Windows Forms application to the current Visual Studio solution. Open its property pages and locate Services tab. This tab allows you to enable client application services for the Windows application. Ensure that the "Enable client application services" checkbox is checked. Also, specify authentication service location, roles service location and web settings (Profile) service location to http://localhost:5555/ClientAppServHost.

image

This way the Windows Forms application knows how to connect with the appropriate membership, roles and profile provider.

Retrieve profile properties in Windows Forms application

In order to access profile properties in Windows applications in strongly typed fashion you need to retrieve them from the web site. To do so open properties tab of the Windows application and select its Settings tab.

image

Click on "Load Web Settings" option to open a login dialog as shown below:

image

Enter user ID and password of any one user of the web site and click "Log In". This will load profile properties in the grid of Settings tab (see Settings tab screenshot above).

Consuming client application services

Now we arrive at the last step. Design the default Windows form from your application as shown below:

image

In the Click event handler of Login button add the following code:

private void btnLogin_Click
(object sender, EventArgs e)
{
string msg = "Welcome ";
if (!Membership.ValidateUser(txtUserID.Text, 
txtPassword.Text))
{
MessageBox.Show("Invalid User ID or Password!");
}
else
{
msg = msg + txtUserID.Text;
}
if (Thread.CurrentPrincipal.IsInRole("Manager"))
{
msg = msg + " [Manager]";
}
if (Thread.CurrentPrincipal.IsInRole("Operator"))
{
msg = msg + " [Operator]";
}
MessageBox.Show(msg);
...
txtFullName.Text = Properties.Settings.
Default.FullName;
}

Here, we used Validate() method of membership class to check if the user ID and password are valid. If so you check if the user belongs to Manager role. This is done using IsInRole() method of the Principal object of current thread. This principle is automatically populated with appropriate identity and role information. Finally, FullName profile property is read using Settings collection. Notice how the FullName property is accessed in typed fashion.

Now add the following code in the Click event handler of Save button.

private void btnSave_Click
(object sender, EventArgs e)
{
Properties.Settings.Default.FullName 
= txtFullName.Text;
Properties.Settings.Default.Save();
}

The code sets the FullName profile property to the new value and calls Save() method. This way the new value gets stored in the database.

Finally add the following code in the Click event hander of Logout button.

private void button3_Click
(object sender, EventArgs e)
{
ClientFormsAuthenticationMembershipProvider 
authProvider = 
(ClientFormsAuthenticationMembershipProvider) 
Membership.Provider;
authProvider.Logout();
...
}

The code accesses membership provider using the Provider property of Membership class. This provider is of type ClientFormsAuthenticationMembershipProvider, a class residing in System.Web.ClientServices.Providers namespace. Logout() method of the provider is then called.

That's it. To test the application create couple of users and roles in the web site using Web Site Administration tool and run the Windows Forms application.

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