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Developing 3 tier application in CSharp using LINQ

The ASP.NET application that we will create we be a 3 tier application, consisting of a data access layer (DAL), a business logic layer (BLL) and a presentation layer (PL).

We will be using Visual Studio Orcas Beta 1 for this tutorial.

Defining our database schema

Before we jump into coding some C# or ASP.NET we need to setup our database, more importantly we first need a database! If you haven’t already go and grab yourself a copy of SQL Express 2005. I will be using SQL Server Management Studio 2005 to create and define my database; however, you can do all of this using Visual Studio 2005 if you want.

Creating a database

Let’s go ahead and create a database for this tutorial. I’m going to create a database called TodoList. To create a database right click the Databases folder in the Object Explorer window and click New Database (Figure 4-1).

Figure 4-1: Creating a database

When the New Database window is visible enter TodoList (or any other name you want to use) as the Database name (Figure 4-2).

Figure 4-2: Specifying the database name

Adding the Tasks table

With our database created we will now add a Tasks table. In SQL Server Management Studio right click the Tables folder and select New Table (Figure 4-3).

Figure 4-3: Creating the Tasks table

In the table designer replicate the settings from Figure 4-4.

Figure 4-4: Defining the columns

Note: In Figure 4-4 TaskID is a primary key and identity.

When you save the table, save it as Tasks (Figure 4-5).

Figure 4-5: Saving the table

Creating the stored procedures

We need to define three stored procedures, one for adding a new task, one for updating the state of a task, and finally one for retrieving all tasks of a specific state (either active, or closed).

Creating a stored procedure is easy, simply right click on the Stored Procedures folder and click New Stored Procedure (Figure 4-6).

Figure 4-6: Creating a stored procedure

Below are the three code listings for the stored procedures we will use.

Figure 4-7: AddTask

  1. create procedure AddTask
  2. @Title nvarchar(50),
  3. @Complete bit
  4. as
  5. insert into Tasks (Title, Complete)
  6. values (@Title, @Complete)

Figure 4-8: GetTasksByState

  1. create procedure GetTasksByState
  2. @Complete bit
  3. as
  4. select TaskID, Title, Complete
  5. from Tasks
  6. where Complete = @Complete
  7. order by Title

Figure 4-9: UpdateTaskState

  1. create procedure UpdateTaskState
  2. @TaskID int,
  3. @Complete bit
  4. as
  5. update Tasks
  6. set Complete = @Complete
  7. where TaskID = @TaskID

Setting up our data access layer

With our database ready let’s go ahead and create our DAL. We will use the LINQ to SQL file designer in Visual Studio Orcas to do this.

Note: You will first need to add a connection to the TodoList database in the Server Explorer window.

Right click on your website project and add a new LINQ to SQL file called TodoList (Figure 4-10).

Figure 4-10: Adding a LINQ to SQL file to our project

With the file created drag and drop the Tasks table and the three stored procedures we created on to the design canvas of the designer (Figure 4-11).

Figure 4-11: Adding our table and sprocs to our DAL

That’s it! Our DAL is all ready to use.

Adding a business logic layer

In this tutorial there is not much point to adding a BLL, but we will add one nonetheless.

This layer in a real life application this layer would enforce any business rules (parameter checking etc…). Also in a real life application you would want to separate your DAL and BLL into their own components.

Right click the App_Code folder and add a new class called TasksBll.cs, then copy and paste the class definition given in Figure 4-12 into that file.

Figure 4-12: TasksBll.cs

  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4. namespace Org.GBarnett.Dns
  5. {
  6. public static class TasksBll
  7. {
  8. /// <summary>
  9. /// Gets all tasks of a particular state
  10. /// </summary>
  11. public static List<GetTasksByState> GetTasksByState()
  12. {
  13. using (TodoListDataContext db = new TodoListDataContext())
  14. {
  15. return (from t in db.GetTasksByState() select t).ToList<GetTasksByState>();
  16. }
  17. }
  18. /// <summary>
  19. /// Adds a new task
  20. /// </summary>
  21. public static void AddTask(string title, bool complete)
  22. {
  23. using (TodoListDataContext db = new TodoListDataContext())
  24. {
  25. db.AddTask(title, complete);
  26. }
  27. }
  28. /// <summary>
  29. /// Updates a tasks state
  30. /// </summary>
  31. public static void UpdateTaskState(int taskId, bool complete)
  32. {
  33. using (TodoListDataContext db = new TodoListDataContext())
  34. {
  35. db.UpdateTaskState(taskId, complete);
  36. }
  37. }
  38. }
  39. }

Each method of the TasksBll.cs (Figure 4-12) performs the appropriate operation by accessing methods defined in our DAL.

Enter ASP.NET…

As previously mentioned we will use ASP.NET to define the UI.

The UI will consist of 3 controls:

  • DropDownList
  • GridView
  • FormView

Before we begin add a new AJAX Web Form to your project, the name you give it is irrelevant. Add all the following code snippets inside the form tag of the page.

We have two states

Either a task is active or complete. We will use a drop down list control to store these values (Figure 4-12).

Figure 4-13: DropDownList containing the tasks states

  1. <asp:DropDownList ID=“ddlState” runat=“server” AutoPostBack=“true”>
  2. <asp:ListItem Selected=“True” Text=“Active” Value=“false” />
  3. <asp:ListItem Text=“Complete” Value=“true” />
  4. </asp:DropDownList>

Adding an ObjectDataSource

Before we add any more controls to our web page we need to hook our presentation layer up with our BLL. To do this we will add an ObjectDataSource and wire it up to the appropriate methods defined in our BLL.

Figure 4-14: Adding an ObjectDataSource

  1. <asp:ObjectDataSource
  2. ID=“odsTasks”
  3. runat=“server”
  4. TypeName=“TasksBll”
  5. SelectMethod=“GetTasksByState”
  6. InsertMethod=“AddTask”
  7. UpdateMethod=“UpdateTaskState”>
  8. <SelectParameters>
  9. <asp:ControlParameter
  10. ControlID=“ddlState”
  11. Name=“complete”
  12. PropertyName=“SelectedValue”
  13. Type=“Boolean” />
  14. </SelectParameters>
  15. <UpdateParameters>
  16. <asp:Parameter Name=“taskId” Type=“int32” />
  17. <asp:Parameter Name=“complete” Type=“boolean” />
  18. </UpdateParameters>
  19. <InsertParameters>
  20. <asp:Parameter Name=“title” Type=“string” />
  21. <asp:Parameter Name=“complete” Type=“boolean” />
  22. </InsertParameters>
  23. </asp:ObjectDataSource>

Using a GridView to view the tasks

We will now go ahead and add a GridView to our page (Figure 4-15).

Note: I have customized the Item and Edit templates for the checkbox control.

Figure 4-15: Adding a GridView to our page to display the tasks

  1. <asp:GridView
  2. ID=“gvTasks”
  3. runat=“server”
  4. DataSourceID=“odsTasks”
  5. AutoGenerateColumns=“false”
  6. DataKeyNames=“TaskID”
  7. AllowPaging=“true”
  8. GridLines=“None”
  9. AlternatingRowStyle-CssClass=“alternate”>
  10. <Columns>
  11. <asp:BoundField DataField=“Title” HeaderText=“Task” ReadOnly=“true” />
  12. <asp:TemplateField HeaderText=“Complete”>
  13. <ItemTemplate>
  14. <asp:CheckBox ID=“cbI” runat=“server” Checked=‘<%# Eval(“Complete”) %>’
  15. Enabled=“false” />
  16. </ItemTemplate>
  17. <EditItemTemplate>
  18. <asp:CheckBox ID=“cbE” runat=“server” Checked=‘<%# Bind(“Complete”) %>’ />
  19. </EditItemTemplate>
  20. </asp:TemplateField>
  21. <asp:CommandField ShowEditButton=“true” />
  22. </Columns>
  23. </asp:GridView>

Using the FormView to add more tasks

To add a new task we will use a FormView (Figure 4-16).

Note: I have not included any data input checking to keep the example as simple as possible.

Figure 4-16: Adding a FormView to allow the user to add new tasks

  1. <asp:FormView ID=“fvTask” runat=“server” DefaultMode=“Insert” DataSourceID=“odsTasks”>
  2. <InsertItemTemplate>
  3. <p><strong>Title:</strong>
  4. <asp:TextBox ID=“txtTitle” runat=“server” Text=‘<%# Bind(“Title”) %>’ /></p>
  5. <p><strong>Complete:</strong>
  6. <asp:CheckBox ID=“cbC” runat=“server” Checked=‘<%# Bind(“Complete”) %>’ /></p>
  7. <p><asp:LinkButton ID=“lbAdd” runat=“server” Text=“Add Task” CommandName=“Insert” /></p>
  8. </InsertItemTemplate>
  9. </asp:FormView>

Adding AJAX functionality to the GridView and the FormView controls

Just to smooth things up I’ve added a few UpdatePanel’s to the page, each wrapping the GridView and FormView respectively.

Figure 4-17: The updated GridView

  1. <asp:UpdatePanel ID=“upTasks” runat=“server”>
  2. <ContentTemplate>
  3. <asp:GridView
  4. ID=“gvTasks”
  5. runat=“server”
  6. DataSourceID=“odsTasks”
  7. AutoGenerateColumns=“false”
  8. DataKeyNames=“TaskID”
  9. AllowPaging=“true”
  10. GridLines=“None”
  11. AlternatingRowStyle-CssClass=“alternate”>
  12. <Columns>
  13. <asp:BoundField DataField=“Title” HeaderText=“Task” ReadOnly=“true” />
  14. <asp:TemplateField HeaderText=“Complete”>
  15. <ItemTemplate>
  16. <asp:CheckBox ID=“cbI”
  17. runat=“server”
  18. Checked=‘<%# Eval(“Complete”) %>’
  19. Enabled=“false” />
  20. </ItemTemplate>
  21. <EditItemTemplate>
  22. <asp:CheckBox ID=“cbE” runat=“server” Checked=‘<%# Bind(“Complete”) %>’ />
  23. </EditItemTemplate>
  24. </asp:TemplateField>
  25. <asp:CommandField ShowEditButton=“true” />
  26. </Columns>
  27. </asp:GridView>
  28. </ContentTemplate>
  29. <Triggers>
  30. <asp:AsyncPostBackTrigger ControlID=“ddlState” />
  31. </Triggers>
  32. </asp:UpdatePanel>

Figure 4-18: The update FormView

  1. <asp:UpdatePanel ID=“upAdd” runat=“server”>
  2. <ContentTemplate>
  3. <asp:FormView ID=“fvTask” runat=“server” DefaultMode=“Insert” DataSourceID=“odsTasks”>
  4. <InsertItemTemplate>
  5. <p><strong>Title:</strong>
  6. <asp:TextBox ID=“txtTitle” runat=“server” Text=‘<%# Bind(“Title”) %>’ /></p>
  7. <p><strong>Complete:</strong>
  8. <asp:CheckBox ID=“cbC” runat=“server” Checked=‘<%# Bind(“Complete”) %>’ /></p>
  9. <p>
  10. <asp:LinkButton ID=“lbAdd” runat=“server” Text=“Add Task” CommandName=“Insert” />
  11. </p>
  12. </InsertItemTemplate>
  13. </asp:FormView>
  14. </ContentTemplate>
  15. </asp:UpdatePanel>

And on that note we are finished! You can download the full source code at the end of this tutorial.

The experience

From personal experience coding the data access layer can be a very boring process – in this tutorial we have seen how effective LINQ to SQL can be when creating our DAL.

Visual Studio Orcas has introduced a few really cool tools to further assist with the creation of the DAL – we no longer need to spend hours on OR mapping. The great thing about LINQ is the ability to further query your DAL, and create some anonymous type.

There is no doubt in my mind that LINQ is set to revolutionize the way programmers interact with data, more so is the fact that we always use a familiar set of standard query operators!

If you download and run the source you will see the site shown in Figure 4-19.

Figure 4-19: Our to-do list web site