Walkthrough: Creating an N-Tier Data Application

N-tier* data applications are applications that access data and are separated into multiple logical layers, or tiers. Separating application components into discrete tiers increases the maintainability and scalability of the application. It does this by enabling easier adoption of new technologies that can be applied to a single tier without requiring you to redesign the whole solution. N-tier architecture includes a presentation tier, a middle-tier, and a data tier. The middle tier typically includes a data access layer, a business logic layer, and shared components such as authentication and validation. The data tier includes a relational database. N-tier applications usually store sensitive information in the data access layer of the middle-tier to maintain isolation from end users who access the presentation tier. For more information, see N-Tier Data Applications Overview.

One way to separate the various tiers in an n-tier application is to create discrete projects for each tier that you want to include in your application. Typed datasets contain a DataSet Project property that determines which projects the generated dataset and TableAdapter code should go into.

This walkthrough demonstrates how to separate dataset and TableAdapter code into discrete class library projects by using the Dataset Designer. After you separate the dataset and TableAdapter code, you will create a Windows Communication Foundation Services and WCF Data Services in Visual Studio service to call into the data access tier. Finally, you will create a Windows Forms application as the presentation tier. This tier accesses data from the data service.

During this walkthrough, you will perform the following steps:

• Create a new n-tier solution that will contain multiple projects.

• Add two class library projects to the n-tier solution.

• Create a typed dataset by using the Data Source Configuration Wizard.

• Separate the generated TableAdapters and dataset code into discrete projects.

• Create a Windows Communication Foundation (WCF) service to call into the data access tier.

• Create functions in the service to retrieve data from the data access tier.

• Create a Windows Forms application to serve as the presentation tier.

• Create Windows Forms controls that are bound to the data source.

• Write code to populate the data tables.

  For a video version of this topic, see Video How to: Creating an N-Tier Data Application.

Prerequisites

To complete this walkthrough, you need:

• Access to the Northwind sample database.

Creating the N-Tier Solution and Class Library to Hold the Dataset (DataEntityTier)

The first step of this walkthrough is to create a solution and two class library projects. The first class library will hold the dataset (the generated typed DataSet class and DataTables that will hold the application's data). This project is used as the data entity layer of the application and is typically located in the middle tier. The Dataset Designer is used to create the initial dataset and automatically separate the code into the two class libraries.

To create the n-tier solution and DataEntityTier class library

1. From the File menu, create a new project.

   Note

   The Dataset Designer is supported in Visual Basic and C# projects. Create the new project in one of these languages.

2. In the New Project dialog box, in the Project types pane, click Windows.

3. Click the Class Library template.

4. Name the project DataEntityTier.

5. Name the solution NTierWalkthrough.

6. Click OK.

   An NTierWalkthrough solution that contains the DataEntityTier project is created and added to Solution Explorer.

Creating the Class Library to Hold the TableAdapters (DataAccessTier)

The next step after you create the DataEntityTier project is to create another class library project. This project will hold the generated TableAdapters and is called the data access tier of the application. The data access tier contains the information that is required to connect to the database and is typically located in the middle tier.

To create the new class library for the TableAdapters

1. From the File menu, add a new project to the NTierWalkthrough solution.

2. In the New Project dialog box, in the Templates pane, click Class Library.

3. Name the project DataAccessTier and click OK.

   The DataAccessTier project is created and added to the NTierWalkthrough solution.

Creating the Dataset

The next step is to create a typed dataset. Typed datasets are created with both the dataset class (including DataTables classes) and the TableAdapter classes in a single project. (All classes are generated into a single file.) When you separate the dataset and TableAdapters into different projects, it is the dataset class that is moved to the other project, leaving the TableAdapter classes in the original project. Therefore, create the dataset in the project that will ultimately contain the TableAdapters (the DataAccessTier project). You will create the dataset by using the Data Source Configuration Wizard.

To create the dataset

1. Click DataAccessTier in Solution Explorer.

2. On the Data menu, click Show Data Sources.

3. In the Data Sources window, click Add New Data Source to start the Data Source Configuration Wizard.

4. On the Choose a Data Source Type page, click Database and then click Next.

5. On the Choose Your Data Connection page, perform one of the following actions:

   If a data connection to the Northwind sample database is available in the drop-down list, click it.

   -or-

   Click New Connection to open the Add Connection dialog box.

6. If the database requires a password, select the option to include sensitive data, and then click Next.

   Note

   If you selected a local database file (instead of connecting to SQL Server) you might be asked if you want to add the file to the project. Click Yes to add the database file to the project.

7. Click Next on the Save the Connection String to the Application Configuration File page.

8. Expand the Tables node on the Choose Your Database Objects page.

9. Click the check boxes for the Customers and Orders tables, and then click Finish.

   NorthwindDataSet is added to the DataAccessTier project and appears in the Data Sources window.

Separating the TableAdapters from the Dataset

After you create the dataset, separate the generated dataset class from the TableAdapters. You do this by setting the DataSet Project property to the name of the project in which to store the separated out dataset class.

To separate the TableAdapters from the Dataset

1. Double-click NorthwindDataSet.xsd in Solution Explorer to open the dataset in the Dataset Designer.

2. Click an empty area on the designer.

3. Locate the DataSet Project node in the Properties window.

4. In the DataSet Project list, click DataEntityTier.

5. On the Build menu, click Build Solution.

   The dataset and TableAdapters are separated into the two class library projects. The project that originally contained the whole dataset (DataAccessTier) now contains only the TableAdapters. The project designated in the DataSet Project property (DataEntityTier) contains the typed dataset: NorthwindDataSet.Dataset.Designer.vb (or NorthwindDataSet.Dataset.Designer.cs).

Creating a New Service Application

Because this walkthrough demonstrates how to access the data access tier by using a WCF service, create a new WCF service application.

To create a new WCF Service application

1. From the File menu, add a new project to the NTierWalkthrough solution.

2. In the New Project dialog box, in the Project types pane, click WCF. In the Templates pane, click WCF Service Library.

3. Name the project DataService and click OK.

   The DataService project is created and added to the NTierWalkthrough solution.

Creating Methods in the Data Access Tier to Return the Customers and Orders Data

The data service has to call two methods in the data access tier: GetCustomers and GetOrders. These methods will return the Northwind Customers and Orders tables. Create the GetCustomers and GetOrders methods in the DataAccessTier project.

To create a method in the data access tier that returns the Customers table

1. In Solution Explorer, double-click NorthwindDataset.xsd to open the dataset in the Dataset Designer.

2. Right-click CustomersTableAdapter and click Add Query to edit the Tableadapter.

3. On the Choose a Command Type page, leave the default value of Use SQL statements and click Next.

4. On the Choose a Query Type page, leave the default value of SELECT which returns rows and click Next.

5. On the Specify a SQL SELECT statement page, leave the default query and click Next.

6. On the Choose Methods to Generate page, type GetCustomers for the Method name in the Return a DataTable section.

7. Click Finish.

To create a method in the data access tier that returns the Orders table

1. Right-click OrdersTableAdapter and click Add Query.

2. On the Choose a Command Type page, leave the default value of Use SQL statements and click Next.

3. On the Choose a Query Type page, leave the default value of SELECT which returns rows and click Next.

4. On the Specify a SQL SELECT statement page, leave the default query and click Next.

5. On the Choose Methods to Generate page, type GetOrders for the Method name in the Return a DataTable section.

6. Click Finish.

7. On the Build menu, click Build Solution.

Adding a Reference to the Data Entity and Data Access Tiers to the Data Service

Because the data service requires information from the dataset and TableAdapters, add references to the DataEntityTier and DataAccessTier projects.

To add references to the data service

1. Right-click DataService in Solution Explorer and click Add Reference.

2. Click the Projects tab in the Add Reference dialog box.

3. Select both the DataAccessTier and DataEntityTier projects.

4. Click OK.

Adding Functions to the Service to Call the GetCustomers and GetOrders Methods in the Data Access Tier

Now that the data access tier contains the methods to return data, create methods in the data service to call the methods in the data access tier.

To create the GetCustomers and GetOrders functions in the data service

1. In the DataService project, double-click IService1.vb or IService1.cs.

2. Add the following code under the Add your service operations here comment:

   <OperationContract()> _
   Function GetCustomers() As DataEntityTier.NorthwindDataSet.CustomersDataTable
   
   <OperationContract()> _
   Function GetOrders() As DataEntityTier.NorthwindDataSet.OrdersDataTable
   

   [OperationContract]
   DataEntityTier.NorthwindDataSet.CustomersDataTable GetCustomers();
   
   [OperationContract]
   DataEntityTier.NorthwindDataSet.OrdersDataTable GetOrders();
   
   

3. In the DataService project, double-click Service1.vb (or Service1.cs).

4. Add the following code to the Service1 class:

   Public Function GetCustomers() As DataEntityTier.NorthwindDataSet.CustomersDataTable Implements IService1.GetCustomers
       Dim CustomersTableAdapter1 As New DataAccessTier.NorthwindDataSetTableAdapters.CustomersTableAdapter
       Return CustomersTableAdapter1.GetCustomers()
   End Function
   
   Public Function GetOrders() As DataEntityTier.NorthwindDataSet.OrdersDataTable Implements IService1.GetOrders
       Dim OrdersTableAdapter1 As New DataAccessTier.NorthwindDataSetTableAdapters.OrdersTableAdapter
       Return OrdersTableAdapter1.GetOrders()
   End Function
   

   public DataEntityTier.NorthwindDataSet.CustomersDataTable GetCustomers()
   {
       DataAccessTier.NorthwindDataSetTableAdapters.CustomersTableAdapter
            CustomersTableAdapter1
           = new DataAccessTier.NorthwindDataSetTableAdapters.CustomersTableAdapter();
       return CustomersTableAdapter1.GetCustomers();
   
   }
   public DataEntityTier.NorthwindDataSet.OrdersDataTable GetOrders()
   {
       DataAccessTier.NorthwindDataSetTableAdapters.OrdersTableAdapter
            OrdersTableAdapter1
           = new DataAccessTier.NorthwindDataSetTableAdapters.OrdersTableAdapter();
       return OrdersTableAdapter1.GetOrders();
   
   }
   

5. On the Build menu, click Build Solution.

Creating a Presentation Tier to Display Data from the Data Service

Now that the solution contains the data service that has methods that call into the data access tier, create another project that will call into the data service and present the data to users. For this walkthrough, create a Windows Forms application; this is the presentation tier of the n-tier application.

To create the presentation tier project

1. From the File menu, add a new project to the NTierWalkthrough solution.

2. In the New Project dialog box, in the Project types pane, click Windows. In the Templates pane, click Windows Forms Application.

3. Name the project PresentationTier and click OK.

4. The PresentationTier project is created and added to the NTierWalkthrough solution.

Setting the PresentationTier Project as the Startup Project

Because the presentation tier is the actual client application that is used to present and interact with the data, you must set the PresentationTier project to be the Startup project.

To set the new presentation tier project as the Startup project

• In Solution Explorer, right-click PresentationTier and click Set as StartUp Project.

Adding References to the Presentation Tier

The client application PresentationTier requires a service reference to the data service in order to access the methods in the service. In addition, a reference to the dataset is required to enable type sharing by the WCF service. Until you enable type sharing through the data service, code added to the partial dataset class will not be available to the presentation tier. Because you typically add code such as validation to the row and column changing events of a data table, it is likely that you will want to access this code from the client.

To add a reference to the presentation tier

1. In Solution Explorer, right-click PresentationTier and click Add Reference.

2. In the Add Reference dialog box, click the Projects tab.

3. Select DataEntityTier and click OK.

To add a service reference to the presentation tier

1. In Solution Explorer, right-click PresentationTier and click Add Service Reference.

2. In the Add Service Reference dialog box, click Discover.

3. Select Service1 and click OK.

   Note

   If you have multiple services on the current computer, select the service that you created previously in this walkthrough (the service that contains the GetCustomers and GetOrders methods).

Adding DataGridViews to the Form to Display the Data Returned by the Data Service

After you add the service reference to the data service, the Data Sources window is automatically populated with the data that is returned by the service.

To add two data bound DataGridViews to the form

1. In Solution Explorer, select the PresentationTier project.

2. In the Data Sources window, expand NorthwindDataSet and locate the Customers node.

3. Drag the Customers node onto Form1.

4. In the Data Sources window, expand the Customers node and locate the related Orders node (the Orders node nested in the Customers node).

5. Drag the related Orders node onto Form1.

6. Create a Form1_Load event handler by double-clicking an empty area of the form.

7. Add the following code to the Form1_Load event handler.

   Dim DataSvc As New ServiceReference1.Service1Client
   NorthwindDataSet.Customers.Merge(DataSvc.GetCustomers)
   NorthwindDataSet.Orders.Merge(DataSvc.GetOrders)
   

   ServiceReference1.Service1Client DataSvc =
       new ServiceReference1.Service1Client();
   northwindDataSet.Customers.Merge(DataSvc.GetCustomers());
   northwindDataSet.Orders.Merge(DataSvc.GetOrders());
   
   

Increasing the Maximum Message Size Allowed by the Service

Because the service returns data from the Customers and Orders tables, the default value for maxReceivedMessageSize is not large enough to hold the data and must be increased. For this walkthrough, you will change the value to 6553600. You will change the value on the client, and this will automatically update the service reference.

To increase the maxReceivedMessageSize value

1. In Solution Explorer, double-click the app.config file in the PresentationTier project.

2. Locate the maxReceivedMessage size attribute and change the value to 6553600.

Testing the Application

Run the application. The data is retrieved from the data service and displayed on the form.

To test the application

1. Press F5.

2. The data from the Customers and Orders tables is retrieved from the data service and displayed on the form.

Next Steps

Depending on your application requirements, there are several steps that you may want to perform after you save related data in the Windows-based application. For example, you could make the following enhancements to this application:

• Add validation to the dataset. For information, see Walkthrough: Adding Validation to an N-Tier Data Application.

• Add additional methods to the service for updating data back to the database.

See Also

Work with datasets in n-tier applications Hierarchical update Accessing data in Visual Studio