Evjen c08.tex V2 - 01/28/2008 2:05pm Page 396 Chapter 8: Data Management with ADO.NET XML file. It didn’t even allow you to serialize the DataTable object independently of the larger and encompassing DataSet object. This limitation required you to always use the DataSet object to perform any operation on a DataTable . T he current version of ADO.NET removes this limitation and enables you to work directly with the DataTable for all your needs. In fact, we recommend that you don’t use the DataSet object unless you need to work with multiple DataTable objects and need a container object to manage them. If you end up working with only a single table of information, then it is best to work with an instance of the DataTable object rather than a DataSet that contains only a single DataTable . The current version of ADO.NET provides the capability to load a DataTable in memory by consuming a data source using a DataReader . In the past, you were sometimes restricted to creating multiple overloads of the same method just to work with both the DataReader and the DataTable objects. Now you have the flexibility to write the data access code one time and reuse the DataReader — either directly or to fill a DataTable , as shown in Listing 8-11. Listing 8-11: How to load a DataTable from a DataReader VB < %@ Page Language="VB" % > < %@ Import Namespace="System.Data" % > < %@ Import Namespace="System.Data.SqlClient" % > < %@ Import Namespace="System.Configuration" % > < script runat="server" > Protected Sub Page_Load(ByVal sender As Object, _ ByVal e As System.EventArgs) If Not Page.IsPostBack Then Dim MyDataTable As DataTable Dim MyReader As SqlDataReader Dim CityParam As SqlParameter Dim MyConnection As SqlConnection = New SqlConnection() MyConnection.ConnectionString = _ ConfigurationManager.ConnectionStrings("DSN_Northwind").ConnectionString Dim MyCommand As SqlCommand = New SqlCommand() MyCommand.CommandText = _ "SELECT * FROM CUSTOMERS WHERE CITY = @CITY" MyCommand.CommandType = CommandType.Text MyCommand.Connection = MyConnection CityParam = New SqlParameter() CityParam.ParameterName = "@CITY" CityParam.SqlDbType = SqlDbType.VarChar CityParam.Size = 15 CityParam.Direction = ParameterDirection.Input CityParam.Value = "London" MyCommand.Parameters.Add(CityParam) MyCommand.Connection.Open() Continued 396 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 397 Chapter 8: Data Management with ADO.NET MyReader = MyCommand.ExecuteReader(CommandBehavior.CloseConnection) MyDataTable = New DataTable() ’ Loading DataTable using a DataReader MyDataTable.Load(MyReader) gvCustomers.DataSource = MyDataTable gvCustomers.DataBind() MyDataTable.Dispose() MyCommand.Dispose() MyConnection.Dispose() End If End Sub < /script > C# < %@ Page Language="C#" % > < %@ Import Namespace="System.Data" % > < %@ Import Namespace="System.Data.SqlClient" % > < %@ Import Namespace="System.Configuration" % > < script runat="server" > protected void Page_Load(object sender, EventArgs e) { if (!Page.IsPostBack ) { DataTable MyDataTable; SqlDataReader MyReader; SqlParameter CityParam; SqlConnection MyConnection = new SqlConnection(); MyConnection.ConnectionString = ConfigurationManager.ConnectionStrings["DSN_Northwind"].ConnectionString; SqlCommand MyCommand = new SqlCommand(); MyCommand.CommandText = "SELECT * FROM CUSTOMERS WHERE CITY = @CITY"; MyCommand.CommandType = CommandType.Text; MyCommand.Connection = MyConnection; CityParam = new SqlParameter(); CityParam.ParameterName = "@CITY"; CityParam.SqlDbType = SqlDbType.VarChar; CityParam.Size = 15; CityParam.Direction = ParameterDirection.Input; CityParam.Value = "London"; MyCommand.Parameters.Add(CityParam); Continued 397 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 398 Chapter 8: Data Management with ADO.NET MyCommand.Connection.Open(); MyReader = MyCommand.ExecuteReader(CommandBehavior.CloseConnection); MyDataTable = new DataTable(); // Loading DataTable using a DataReader MyDataTable.Load(MyReader); gvCustomers.DataSource = MyDataTable; gvCustomers.DataBind(); MyDataTable.Dispose(); MyCommand.Dispose(); MyConnection.Dispose(); } } < /script > Not only can you load a DataTable object from a DataReader object, you can also retrieve a DataTableReader from an existing DataTable object. This is accomplished by calling the Create- DataReader method of the DataTable class. This method returns an instance of the DataTableReader object that can be passed to any method that expects to receive a DataReader . Deciding When to Use a DataSet As revolutionary as a DataSet might be, it is not the best choice in every situation. Often, it may not be appropriate to use a DataSet ; instead it might be better to use a DataReader . With ADO 2.6, it was possible to perform a command upon a data store and get back a single collection of data made up of any number of rows. You could then iterate through this collection of data and use it in some fashion. Now ADO.NET can use the DataSet to return a collection of data that actually keeps its structure when removed from the data store. In some situations, you benefit greatly from keeping this copy in its original format. By doing so, you can keep the data disconnected in an in-memory cache in its separate tables and work with the tables individually or apply relationships between the tables. You can work with the tables in much the same manner as you do with other relational data sources — using a parent/child relationship. If it is to your advantage to work with certain data with all its relationships in place (in order to enforce a parent/child relationship upon the data); in this case, of course, it is better to use a DataSet as opposed to a DataReader . Because the DataSet is a disconnected copy of the data, you can work with the same records repeatedly without having to go back to the data store. This capability can greatly increase performance and lessen the load upon the server. Having a copy of the data separate from the data store also enables you to continuously handle and shape the data locally. For instance, you might need to repeatedly filter or sort through a collection of data. In this case, it would be of great advantage to work with a DataSet rather than going back and forth to the data store itself. Probably one of the greatest uses of the DataSet is to work w i th multiple data stores and come away with a single collection of data. So for instance, if you have your Customers table within SQL and the orders information for those particular customers within an Oracle database, you can very easily query each data store and create a single DataSet with a Customers and an Orders table in place that you can use in any fashion you choose. The DataSet is just a means of storage for data and doesn’t concern itself with 398 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 399 Chapter 8: Data Management with ADO.NET where the data came from. So, if you are working with data that is coming from multiple data stores, it is to your benefit to use the DataSet . Because the DataSet is based upon XML and XML Schemas, it is quite easy to move the DataSet around — whether you are transporting it across tiers, processes or between disparate systems or applications. If the application or system to which you are transferring the DataSet doesn’t understand DataSet s, the DataSet represents itself as an XML file. So basically, any system or application that can interpret and understand XML can w ork with the DataSet . This makes it a very popular transport vehicle, and you see an example of it when you transport the DataSet from an XML Web service. Last but not least, the DataSet enables you to program data with ease. It is much simpler than anything that has been provided before the .NET Framework came to the scene. Putting the data within a class object allows you to programmatically access the DataSet . The code example in Listing 8-12 shows you just how easy it can be. Listing 8-12: An example of working with the D ataSet object VB Dim conn As SqlConnection = New SqlConnection _ (ConfigurationManager.ConnectionStrings("DSN_Northwind").ConnectionString) conn.Open() Dim da As SqlDataAdapter = New SqlDataAdapter("Select * from Customers", conn) Dim ds As DataSet = New DataSet() da.Fill(ds, "CustomersTable") C# SqlConnection conn = new SqlConnection (ConfigurationManager.ConnectionStrings["DSN_Northwind"].ConnectionString); conn.Open(); SqlDataAdapter da = new SqlDataAdapter("Select * from Customers", conn); DataSet ds = new DataSet(); da.Fill(ds, "CustomersTable"); Basically, when you work with data, you have to weigh when to use the DataSet . In some cases, you get extreme benefits from using this piece of technology that is provided with ADO.NET. Sometimes, however, you may find it is not in your best interests to use the DataSet . Instead, it is best to use the DataReader . The DataSet can be used whenever you choose, but sometimes you would rather use the DataReader and work directly against the data store. By using the command objects, such as the SqlCommand and the OleDbCommand objects, you have a little more direct control over what is executed and what you get back as a result set. In situations where this is vital, it is to your advantage not to use the DataSet . When you don’t use the DataSet , you don’t incur the cost of extra overhead because you are reading and writing directly to the data source. Performing operations in this manner means you don’t have to instantiate any additional objects — avoiding unnecessary steps. This is especially true in a situation when you work with Web Forms in ASP.NET. If you are dealing with Web Forms, the Web pages are re-created each and every time. When this happens, not only is the page re-created by the call to the data source, the DataSet is also re-created unless you are caching the DataSet in some fashion. This can be an expensive process; so, in situations such as this, you might find 399 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 400 Chapter 8: Data Management with ADO.NET it to your benefit to work directly off the data source using the DataReader . In most situations when you are working with Web Forms, you want to work with the DataReader instead of creating a DataSet . The Typed DataSet As powerful as the DataSet is, it still has some limitations. The DataSet is created at runtime. It accesses particular pieces of data by making certain assumptions. Take a look at how you normally access a specific field in a DataSet that is not strongly typed (Listing 8-13). Listing 8-13: Accessing a field in a DataSet VB ds.Tables("Customers").Rows(0).Columns("CompanyName") = "XYZ Company" C# ds.Tables["Customers"].Rows[0].Columns["CompanyName"] = "XYZ Company"; The preceding code looks at the Customers table , the first row (remember, everything is zero-based) in the column CompanyName , and assigns the value of XYZ Company to the field. This is pretty simple and straightforward, but it is based upon certain assumptions and is generated at runtime. The "Customers" and "CompanyName" words are string literals in this line of code. If they are spelled wrong or if these items aren’t in the table, an error occurs at runtime. Listing 8-14 shows you how to assign the same value to the same field by using a typed DataSet . Listing 8-14: Accessing a field in a typed DataSet VB ds.Customers(0).CompanyName = "XYZ Company" C# ds.Customers[0].CompanyName = "XYZ Company"; Now the table name and the field to be accessed are not treated as string literals but, instead, are encased in an XML Schema and a class that is generated from the DataSet class. When you create a typed DataSet , you are creating a class that implements the tables and fields based upon the schema used to generate the class. Basically, the schema is coded into the class. As you compare the two examples, you see that a typed DataSet is easier to read and understand. It is less error-prone, and errors are realized at compile time as opposed to runtime. In the end, typed DataSet s are optional, and you are free to use either style as you code. Using Oracle as Your Database with ASP.NET 3.5 If you work in the enterprise space, in many cases you must work with an Oracle back-end database. ADO.NET 2.0 has a built-in capability to work with Oracle using the System.Data.OracleClient namespace. First, in order to connect ASP.NET to your Oracle database, you install the Oracle 10 g Client on your Web server. You can get this piece of software from the Oracle Web site found at oracle.com .Ifyou 400 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 401 Chapter 8: Data Management with ADO.NET are able to connect to your Oracle database from your Web server using SQL*Plus (an Oracle IDE f or working with an Oracle database), can use the Microsoft-built Oracle data provider, System.Data .OracleClient . If you are still having trouble connecting to your Oracle database, you also may try to make sure that the database connection is properly defined in your server’s .ora file found at C: \ Oracle \ product \ 10.1.0 \ Client_1 \ NETWORK \ ADMIN . Note t hat the version number might be different. After you know you can connect to Oracle, you can make use of the Microsoft-built Oracle data provider. To utilize the built-in capabilities to connect to Oracle, your ASP.NET application must reference this DLL. To do this, right-click your project in the Visual Studio Solution Explorer and select Add Reference from the list of options presented. This gives you a long list of available .NET components. Select the System.Data.OracleClient component . Notice the two versions of this component (as illustrated in Figure 8-4). You select the one that is built for the .NET Framework 2.0. Figure 8-4 After this is added, you find the reference to this component in the web.config file of your ASP.NET application (as presented in Listing 8-15). 401 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 402 Chapter 8: Data Management with ADO.NET Listing 8-15: The reference to the S ystem.Data.OracleClient DLL in the web.config < configuration > < system.web > < compilation debug="true" > < assemblies > < add assembly="System.Data.OracleClient, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/ > < /assemblies > < /compilation > < /system.web > < /configuration > With this reference in place, you also reference this available DLL in your page along with System.Data . This is demonstrated in Listing 8-16. Listing 8-16: Referencing the System.Data.OracleClient DLL VB Imports System.Data Imports System.Data.OracleClient C# using System.Data; using System.Data.OracleClient; With all the references in place, you are able to work with an Oracle backend in pretty much the same manner as you work with a SQL Server backend. Listing 8-17 shows you just how similar it is. Listing 8-17: Using the OracleClient object to connect to an Oracle database VB Dim conn As OracleConnection Dim cmd As OracleCommand Dim cmdString As String = "Select CompanyName from Customers" conn = New _ OracleConnection("User Id=bevjen;Password=bevjen01;Data Source=myOracleDB") cmd = New OracleCommand(cmdString, conn) cmd.CommandType = CommandType.Text conn.Open() C# OracleConnection conn; OracleCommand cmd; string cmdString = "Select CompanyName from Customers"; conn = new OracleConnection("User Id=bevjen;Password=bevjen01;Data Source=myOracleDB"); cmd = new OracleCommand(cmdString, conn); 402 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 403 Chapter 8: Data Management with ADO.NET cmd.CommandType = CommandType.Text; conn.Open(); After you are connected and performing the PL-SQL commands you want, you can use the Oracle- DataReader object just as you would use the SqlDataReader object. Notice that, in this section, I have made reference to the Microsoft-built Oracle data provider. Another option, and many developers consider this the better option, is to use the Oracle-built ODP.NET data provider instead. This data provider can be freely downloaded from the Oracle download page at oracle.com . You can then reference this new DLL in your project. It is now simply a matter of i mport- ing and working with System.DataAccess.OracleClient in your applications. The Oracle-built data provider contains the capability to work with the more advanced feature provided from the Oracle 10 g database. The DataList Server Control The DataList control has been around since the beginning of ASP.NET. It is part of a series of controls that enable you to display your data (especially repeated types of data) using templates. Templates enable you to create more sophisticated layouts for your data and perform functionss that controls such as the GridView server control cannot. Template-based controls like the DataList control require more work on your part. For instance, you have to build common tasks for yourself. You cannot rely on other data controls, which you might be used to, such s as paging. Looking at the Available Templates The idea, when using template-based controls such as the DataList control, is that you put together specific templates to create your desired detailed layout. The DataList control has a number of templates that you can use to build your display. The available templates are defined here in the following table: Template Description AlternatingItemTemplate Works in conjunction with the ItemTemplate to provide a layout for all the odd rows within the layout. This is commonly used if you want to have a grid or layout where each row is distinguished in some way (such as having a different background color). EditItemTemplate Allows for a row or item to be defined on how it looks and behaves when editing. FooterTemplate Allows the last item in the template to be defined. If this is not defined, then no footer will be used. HeaderTemplate Allows the first item in the template to be defined. If this is not defined, then no header will be used. ItemTemplate The core template that is used to define a row or layout for each item in the display. 403 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 404 Chapter 8: Data Management with ADO.NET Template Description SelectedItemTemplate Allows for a row or item to be defined on how it looks and behaves when selected. SeparatorTemplate The layout of any separator that is used between the items in the display. Working with ItemTemplate Although you have seven templates available to you for use with the DataList control, at a minimum, you are going to need the ItemTemplate. The following example, shown here in Listing 8-18, shows the company names from the Northwind database. Listing 8-18: Showing the company names from the Northwind database using DataList < %@ Page Language="VB" AutoEventWireup="false" CodeFile="DataListControl.aspx.vb" Inherits="DataListControl" % > < html xmlns="http://www.w3.org/1999/xhtml" > < head runat="server" > < title > DataList Control < /title > < /head > < body > < form id="form1" runat="server" > < div > < asp:DataList ID="DataList1" runat="server" DataSourceID="SqlDataSource1" > < ItemTemplate > Company Name: < asp:Label ID="CompanyNameLabel" runat="server" Text=’ < %# Eval("CompanyName") % > ’/ > < br / > < br / > < /ItemTemplate > < /asp:DataList > < asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString=" < %$ ConnectionStrings:DSN_Northwind % > " SelectCommand="SELECT [CompanyName] FROM [Customers]" > < /asp:SqlDataSource > < /div > < /form > < /body > < /html > As stated, the DataList control requires, at a minimum, an ItemTemplate element where you define the page layout for each item that is encountered from the data source. In this case, all the data is pulled from the Northwind database sample using the SqlDataSource control. The SqlDataSource control pulls only the CompanyName column from the Customers table. From there, the ItemTemplate section of the DataList control defines two items within it. The first item is a static item, ‘‘Company Name:’’ followed by a single ASP.NET server control, the Label server control. Second, the item is then followed by a couple of standard HTML elements. The Text property of the Label control uses inline data binding (as shown 404 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 405 Chapter 8: Data Management with ADO.NET in the previous chapter of this book) to bind the values that are coming out of the SqlDataSource control. If there were more than one data point coming out of the SqlDataSource control, you can still specifically grab the data point that you are interested in using by specifying the item in the Eval statement. < asp:Label ID="CompanyNameLabel" runat="server" Text=’ < %# Eval("CompanyName") % > ’/ > Using the code from Listing 8-18 gives you the following results as illustrated in Figure 8-5. Figure 8-5 If you then look at the source of the page, you can see that the DataList control uses tables by default to lay out the elements. < table id="DataList1" cellspacing="0" border="0" style="border-collapse:collapse;" > < tr > < td > CompanyName: 405 . component in the web.config file of your ASP. NET application (as presented in Listing 8- 15) . 401 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 402 Chapter 8: Data Management with ADO .NET Listing 8- 15: The. uses inline data binding (as shown 404 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 4 05 Chapter 8: Data Management with ADO .NET in the previous chapter of this book) to bind the values that are coming. store. In some situations, you benefit greatly from keeping this copy in its original format. By doing so, you can keep the data disconnected in an in- memory cache in its separate tables and work