ASP.NET 2.0: A Developeramp;#039;s Notebook [Electronic resources] نسخه متنی

4.8. Connect to a Business Object

Note: Unless you are writing a simple web application, you should
really encapsulate all your business logic into components and then
bind your UI controls (such as the GridView) to the business objects.

A well-designed system uses different tiers for different operations
(such as a three-tier architecture). For example, programmers
frequently encapsulate their business logic in classes separate from
those that handle interactions with the user. In ASP.NET 2.0, you can
expose your data-aware classes to data-bound controls (such as the
GridView) tHRough the ObjectDataSource control.
Doing so will allow changes to be made to either layer (business
logic or UI) without affecting the other.

4.8.1. How do I do that?

To illustrate how you can bind a
GridView control to an object through the ObjectDataSource control,
you will create a class that encapsulates your data access logic and
then use an ObjectDataSource control to bind to it. You will then
bind the GridView control to the ObjectDataSource control. When
you're finished, you'll have a
three-tier application.

Launch Visual Studio 2005 and create a new web site project. Name the
project C:\ASPNET20\chap04-ObjectDataSource.

Add a new App_Code folder to your project by
right-clicking the project name in Solution Explorer and then
selecting Add Folder
App_Code Folder (see Figure 4-45).

Figure 4-45. Adding an App_Code folder to the project.

Add a Web.config file to the project by
right-clicking the project name in Solution Explorer and then
selecting Add New Item Web
Configuration File.

Add the following connection string to
Web.config:

<connectionStrings>
<add name="pubsConnectionString" connectionString="Data 
Source=.\SQLEXPRESS;Initial Catalog=pubs;
Integrated Security=True"
providerName="System.Data.SqlClient" />
</connectionStrings>

Right-click the App_Code folder and select Add
New Item.... Select Class and name it
Authors.vb.

Code Authors.vb as shown in Example 4-9. The Authors class contains a single
methodgetAuthors( )which returns a
data set.

Example 4-9. Authors.vb

Imports System.Data.SqlClient
Imports System.Data
Imports Microsoft.VisualBasic
Public Class Authors
Public Function getAuthors( ) As DataSet
Dim conn As New SqlConnection( _
ConfigurationManager.ConnectionStrings _
("pubsConnectionString").ConnectionString)
Dim adapter As New SqlDataAdapter( _
"SELECT au_id, au_fname, au_lname FROM Authors", conn)
Dim ds As New DataSet
adapter.Fill(ds, "Authors")
Return ds
End Function
End Class

Tip: Remember to save the Authors.vb file before
proceeding to the next step.

Add a GridView control to the default Web Form. In the GridView Tasks
menu, select <New data source...> (see Figure 4-46).

Figure 4-46. Selecting a new data source

Choose Object as the data source in the window that opens (see Figure 4-47). Use the default ID of
ObjectDataSource1 for the data source. Click OK.

Figure 4-47. Select Object as the data source

In the drop-down listbox, select Authors as the
business object (see Figure 4-48). Click Next. You
are essentially binding the ObjectDataSource control to the Authors
class.

Figure 4-48. Selecting the object for the ObjectDataSource control

In the SELECT tab, select the "getAuthors( ),
returns DataSet" method (see Figure 4-49). Click Finish.

Figure 4-49. Selecting the method to bind to the SELECT tab

To test the application, press F5. You should now see the GridView
control populated with records from the Authors table.

Note: If you don't see the getAuthors( ) method,
be sure to save your Authors.vb class file
first.

4.8.2. What about...

...editing the rows in the GridView control
through the ObjectDataSource control?

You can also use the GridView control to update the rows through the
ObjectDataSource control.

Add a new method, updateAuthors( ), to the Authors
class, as shown in Example 4-10.

Example 4-10. updateAuthors( )

    Public Sub updateAuthors(ByVal au_id As String, _
ByVal au_fname As String, _
ByVal au_lname As String)
Dim conn As New SqlConnection( _
ConfigurationManager.ConnectionStrings _
("pubsConnectionString").ConnectionString)
Dim adapter As New SqlDataAdapter( _
"SELECT au_id, au_fname, au_lname " & _
"FROM Authors WHERE au_id=@au_id", conn)
Dim ds As New DataSet
adapter.SelectCommand.Parameters.Add( _
"@au_id", SqlDbType.NVarChar, 11).Value = au_id
adapter.Fill(ds, "Authors")
With ds.Tables(0).Rows(0)
.Item("au_fname") = au_fname
.Item("au_lname") = au_lname
End With
Dim cb As New SqlCommandBuilder(adapter)
adapter.Update(ds, "Authors")
End Sub

Click on the Configure Data Source . . . link in the ObjectDataSource
Tasks menu of the GridView control (see Figure 4-50).

Figure 4-50. Configuring the ObjectDataSource control

Click Next, and in the UPDATE tab, select the updateAuthors( ) method
(see Figure 4-51). The use of the updateAuthors( )
method is to update the changes made to the
GridView back to the database. Click Finish.

Tip: Likewise for inserting and deleting records, you just need to add new
methods to the Authors class and then select them in the INSERT and
DELETE tabs.

Figure 4-51. Selecting a method for the UPDATE tab

Tip: Note that the updateAuthors( ) method has parameters that are the
same as the columns displayed in the GridView control.

On the GridView control, check the Enable Editing checkbox (see Figure 4-52) so that the GridView will
display the Edit links in the leftmost column.

Figure 4-52. Enabling the GridView control to be edited

Press F5 to test the application. The GridView control is now
editable with the changes passed to the updateAuthors( ) method for
updating (see Figure 4-53).

Figure 4-53. Updating a row in the GridView control via the ObjectDataSource control

...using a data component together with the
ObjectDataSource control?

Instead of encapsulating the data access logic within a class, it
would be easier if Visual Studio automatically generated all the
required logic for standard data access tasks such as selecting,
inserting, deleting, and updating. In fact, you can do so using a
data component.

Using the same project, right-click the project name in Solution
Explorer and select Add New Item.... Select Web Form, and name the
form Default2.aspx.

Right-click the project name in Solution Explorer and select Add New
Item.... Select Dataset, and name the data set
Dataset.xsd.

You will be prompted to save the data set in the special
App_Code directory. Click Yes (see Figure 4-54).

Figure 4-54. Saving the XSD file in the App_Code folder

The Data Component Configuration Wizard window will appear. Click
Next.

Use the project's existing connection string
(pubsConnectionString, saved in
Web.config). Click Next (see Figure 4-55).

Figure 4-55. Choosing the connection string to use

In the next window, select the "Use SQL
statements" option. Click Next (see Figure 4-56).

Figure 4-56. Selecting how the data component will access the database

In the box "What data should the table
load?", enter the following SQL statement:

SELECT au_id, au_fname, au_lname FROM Authors

Click the Advanced Options... button and check all three checkboxes
(see Figure 4-57). Essentially, you want the Insert,
Update, and Delete statements to be generated automatically. You
would also use optimistic concurrency to prevent updating conflicts.
Click OK and then Next.

Figure 4-57. Generating all the required SQL statements

In the next window, check the three checkboxes (see Figure 4-58). In this step, you are selecting the methods
to be exposed by the data component. Use the default values and click
Next and then Finish.

Figure 4-58. Generating the methods

Save the project. Configure the GridView control to use a new data
source (see Figure 4-59).

Figure 4-59. Configuring the GridView control to use a new data source

In the next window, select Object as the data source and use the
default name of ObjectDataSource1 as the ID of the
data source. Click OK.

Select the business object
DataSetTableAdapter.authorsTableAdapter (see Figure 4-60). This table adapter is autocompiled based on
the data set you added earlier (Dataset.xsd).
Click Next.

Figure 4-60. Choosing a business object

The SELECT, UPDATE, INSERT, and DELETE tabs will all have a method
assigned to them (see Figure 4-61). Click Finish.

Figure 4-61. Choosing methods for the various operations

Finally, check the Enable Editing and Enable Deleting checkboxes in
the GridView Tasks menu (see Figure 4-62).

Tip: Due to a design decision made by Microsoft, you need to set the
ReadOnly attribute of the au_id field of the GridView control to
false, like this (in Source View):

<asp:BoundField  
ReadOnly="false" HeaderText="au_id"   
DataField="au_id" SortExpression="au_id">
</asp:BoundField>

Note: This is because, by default, the GridView control assumes that
primary keys are not updateable, whereas the data component allows
primary keys to be updated. Thus the GridView control will not pass
primary keys' values to the data component. So when
you try to update the GridView control, you will get an error stating
that the ObjectDataSource control could not find an Update method
with the correct parameters.This behavior might change in the final release of Visual Studio
2005.

Figure 4-62. Enabling the GridView control for editing and deleting

Press F5 to test the application. You will now be able to edit and
delete records in the GridView control.

4.8.3. Where can I learn more?

To learn more about data access in .NET using ADO.NET, check out
the following article: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbcon/html/vbconFundamentalDataConceptsInVisualStudioNET.asp.

To learn what is new in ADO.NET 2.0, check out the MSDN site at
http://msdn.microsoft.com/data/DataAccess/Whidbey/default.aspx.

If you are not familiar with data components, refer to this link for
an introduction: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbcon/html/vbconadonetdatasetcreationinvisualstudionet.asp.