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Working with Data Source Controls and Data-Bound Controls
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FigURE 12-2 The Configure Data Source Wizard in Visual Studio allows you to select the data to be exposed by your data source control.
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The wizard-based UI is a great tool for defining many of your data source declarations. However, it is important that you know the markup syntax for working with these controls. This will help with both programming against the controls and taking the exam. Therefore, the rest of this lesson focuses on the markup (and not the wizard-based UI).
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Each data source control is specialized for the type of data with which it is meant to work. The following sections provide an overview of what makes each of these controls unique. The discussion includes some of the common uses of data source controls, such as binding, filtering, sorting, and modifying data.
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Lesson 1: Connecting to Data with Data Source Controls
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Using Objects as Data Sources with ObjectDataSource
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Many web applications work with a middle tier, or business layer, for retrieving and working with application data. This middle tier encapsulates database code inside classes. Web developers can then call methods on these classes to select, insert, modify, and delete data. With this structure, developers do not have to write direct ADO.NET code, because the code is written by whoever wrote the middle tier. In addition, this middle tier is often reusable across different applications. You can use the ObjectDataSource control in ASP.NET to connect to and work with middletier objects in much the same way that you would work with the other data source objects. This control can be added to a page and configured to create an instance of a middle-tier object and call its methods to retrieve, insert, update, and delete data. The ObjectDataSource control is responsible for the execution lifetime of the object. It creates it and disposes of it. Therefore, the business layer code should be written in a stateless manner. Alternatively, if the business layer uses static methods (or shared methods, in Visual Basic), the ObjectDataSource can use these methods without creating an instance of the actual business object. In this case, however, keep in mind that you could end up with performance issues related to thread contention as multiple requests try to access the same static method. You configure an ObjectDataSource to connect to a class by setting its TypeName attribute to a string that represents a valid type to which the web application has access. This class might be inside your App_Code directory or inside a DLL file to which the website has a reference (it should not be in your webpage s code-behind file). You then set the SelectMethod attribute to a valid method name on the class. The ObjectDataSource control will then call this method when the data is requested. As an example, imagine that you need to write an interface to allow a user to manage the shipper table inside the Northwind database. You might have a business object that can return all the shippers in the database and that looks as follows.
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Sample of Visual Basic Code Public Class Shipper Private Shared _cnnString As String = _ ConfigurationManager.ConnectionStrings("NorthwindConnectionString").ToString Public Shared Function GetAllShippers() As DataTable Dim adp As New SqlDataAdapter( _ "SELECT * FROM shippers", _cnnString) Dim ds As New DataSet("shippers") adp.Fill(ds, "shippers") Return ds.Tables("shippers") End Function End Class
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Sample of C# Code public class Shipper { private static string _cnnString = ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ToString(); public static DataTable GetAllShippers() { SqlDataAdapter adp = new SqlDataAdapter( "SELECT * FROM shippers", _cnnString); DataSet ds = new DataSet("shippers"); adp.Fill(ds, "shippers"); return ds.Tables["shippers"]; } }
The Shipper class just listed returns a DataTable as a result of a call to GetAllShippers. You can configure an ObjectDataSource control to provide this data to a webpage by setting the TypeName and SelectMethod attributes as in the following code.
<asp:ObjectDataSource ID="ObjectDataSource1" runat="server" TypeName="Shipper" SelectMethod="GetAllShippers"> </asp:ObjectDataSource>
You can then use this data source control to bind to a web control (more on this in the next lesson). For example, the following markup binds the ObjectDataSource to a DetailsView control to display the information to the user.
<asp:DetailsView ID="DetailsView1" runat="server" DataSourceID="ObjectDataSource1" AllowPaging="true"> </asp:DetailsView>
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