ptg 904 CHAPTER 19 Building Data Access Components with ADO.NET LISTING 19.31 ShowMovie9.aspx <%@ Page Language=”C#” %> <%@ Import Namespace=”System.Data” %> <!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”> <script runat=”server”> protected void btnReject_Click(object sender, EventArgs e) { Movie9 movie = new Movie9(); movie.RejectChanges(); grdMovies.DataBind(); } protected void btnAccept_Click(object sender, EventArgs e) { Movie9 movie = new Movie9(); movie.AcceptChanges(); grdMovies.DataBind(); } </script> <html xmlns=”http://www.w3.org/1999/xhtml” > FIGURE 19.16 Tracking data row changes. From the Library of Wow! eBook ptg 905 Disconnected Data Access 19 <head id=”Head1” runat=”server”> <title>Show Movie9</title> </head> <body> <form id=”form1” runat=”server”> <div> <h1>Edit Movies</h1> <asp:GridView id=”grdMovies” DataSourceID=”srcMovies” DataKeyNames=”Id” AutoGenerateEditButton=”true” Runat=”server”> <Columns> <asp:TemplateField> <ItemTemplate> <%# ((DataRowView)Container.DataItem).Row.RowState %> </ItemTemplate> </asp:TemplateField> </Columns> </asp:GridView> <br /> <asp:Button id=”btnReject” Text=”Reject Changes” OnClick=”btnReject_Click” Runat=”server” /> <asp:Button id=”btnAccept” Text=”Accept Changes” OnClick=”btnAccept_Click” Runat=”server” /> <asp:ObjectDataSource id=”srcMovies” TypeName=”Movie9” SelectMethod=”GetAll” UpdateMethod=”Update” Runat=”server” /> </div> From the Library of Wow! eBook ptg 906 CHAPTER 19 Building Data Access Components with ADO.NET </form> </body> </html> If you click the Accept Changes button, all the changes made to the rows in the GridView are sent to the database. If you click the Reject Changes button, all the rows revert to their original values. Using the DataView Object The DataView object represents an in-memory database view. You can use a DataView object to create a sortable, filterable view of a DataTable. The DataView object supports three important properties: . Sort—Enables you to sort the rows represented by the DataView. . RowFilter—Enables you to filter the rows represented by the DataView. . RowStateFilter—Enables you to filter the rows represented by the DataView accord- ing to the row state (for example, OriginalRows, CurrentRows, Unchanged). The easiest way to create a new DataView is to use the DefaultView property exposed by the DataTable class like this: Dim dataView1 As DataView = dataTable1.DefaultView; The DefaultView property returns an unsorted, unfiltered view of the data contained in a DataTable. You also can directly instantiate a new DataView object by passing a DataTable, filter, sort order, and DataViewRowState filter to the DataView object’s constructor, like this: DataView dataView1 = new DataView(dataTable1, “BoxOfficeTotals > 100000”, “Title ASC”, DataViewRowState.CurrentRows); This statement creates a new DataView from a DataTable that represents the Movies data- base table. The rows are filtered to include only the movies that have a box office total greater than 100,000 dollars. Also, the rows are sorted by the movie title in ascending order. Finally, all the current rows are represented from the DataTable (as opposed, for instance, to rows that have been deleted). The page in Listing 19.30 illustrates one way that you can use a DataView. In Listing 19.32, a DataView is cached in Session state. You can sort the cached DataView by clicking on the header links rendered by the GridView control (see Figure 19.17). From the Library of Wow! eBook ptg 907 Disconnected Data Access 19 LISTING 19.32 ShowDataView.aspx <%@ Page Language=”C#” %> <%@ Import Namespace=”System.Data” %> <%@ Import Namespace=”System.Data.SqlClient” %> <%@ Import Namespace=”System.Web.Configuration” %> <!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”> <script runat=”server”> void Page_Load() { if (Session[“MoviesToSort”] == null) { string connectionString = WebConfigurationManager.ConnectionStrings[“Movies”].ConnectionString; SqlDataAdapter dad = new SqlDataAdapter( “SELECT Id,Title,Director FROM Movies”, connectionString); DataTable dtblMovies = new DataTable(); dad.Fill(dtblMovies); Session[“MoviesToSort”] = dtblMovies.DefaultView; } if (!Page.IsPostBack) FIGURE 19.17 Sorting a cached DataView. From the Library of Wow! eBook ptg 908 CHAPTER 19 Building Data Access Components with ADO.NET BindMovies(); } void BindMovies() { grdMovies.DataSource = Session[“MoviesToSort”]; grdMovies.DataBind(); } protected void grdMovies_Sorting(object sender, GridViewSortEventArgs e) { DataView dvwMovies = (DataView)Session[“MoviesToSort”]; dvwMovies.Sort = e.SortExpression; BindMovies(); } </script> <html xmlns=”http://www.w3.org/1999/xhtml” > <head id=”Head1” runat=”server”> <title>Show DataView</title> </head> <body> <form id=”form1” runat=”server”> <div> <asp:GridView id=”grdMovies” AllowSorting=”true” OnSorting=”grdMovies_Sorting” Runat=”server” /> </div> </form> </body> </html> Using the DataSet Object The DataSet object represents an in-memory database. A single DataSet can contain one or many DataTable objects. You can define parent/child relationships between the DataTable objects contained in a DataSet. For example, the page in Listing 19.33 contains a TreeView control. The TreeView displays a list of movie categories and, beneath each movie category, a list of matching movies (see Figure 19.18). From the Library of Wow! eBook ptg 909 Disconnected Data Access 19 LISTING 19.33 ShowDataSet.aspx <%@ Page Language=”C#” %> <%@ Import Namespace=”System.Data” %> <%@ Import Namespace=”System.Data.SqlClient” %> <%@ Import Namespace=”System.Web.Configuration” %> <!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”> <script runat=”server”> void Page_Load() { if (!Page.IsPostBack) BuildTree(); } void BuildTree() { // Create Connection string connectionString = WebConfigurationManager.ConnectionStrings[“Movies”].ConnectionString; SqlConnection con = new SqlConnection(connectionString); FIGURE 19.18 Building a TreeView from a DataSet. From the Library of Wow! eBook ptg 910 CHAPTER 19 Building Data Access Components with ADO.NET // Create Movie Categories DataAdapter SqlDataAdapter dadCategories = new SqlDataAdapter( “SELECT Id,Name FROM MovieCategories”, con); // Create Movies DataAdapter SqlDataAdapter dadMovies = new SqlDataAdapter( “SELECT Title,CategoryId FROM Movies”, con); // Add the DataTables to the DataSet DataSet dstMovies = new DataSet(); using (con) { con.Open(); dadCategories.Fill(dstMovies, “Categories”); dadMovies.Fill(dstMovies, “Movies”); } // Add a DataRelation dstMovies.Relations.Add(“Children”, dstMovies.Tables[“Categories”].Columns[“Id”], dstMovies.Tables[“Movies”].Columns[“CategoryId”]); // Add the Movie Category nodes foreach (DataRow categoryRow in dstMovies.Tables[“Categories”].Rows) { string name = (string)categoryRow[“Name”]; TreeNode catNode = new TreeNode(name); TreeView1.Nodes.Add(catNode); // Get matching movies DataRow[] movieRows = categoryRow.GetChildRows(“Children”); foreach (DataRow movieRow in movieRows) { string title = (string)movieRow[“Title”]; TreeNode movieNode = new TreeNode(title); catNode.ChildNodes.Add(movieNode); } } } </script> <html xmlns=”http://www.w3.org/1999/xhtml” > <head id=”Head1” runat=”server”> <title>Show DataSet</title> </head> <body> From the Library of Wow! eBook ptg 911 Executing Asynchronous Database Commands 19 <form id=”form1” runat=”server”> <div> <asp:TreeView id=”TreeView1” Runat=”server” /> </div> </form> </body> </html> The TreeView is built programmatically. In the BuildTree() method, a DataSet is created that contains two DataTable objects. The first DataTable represents the MovieCategories database table, and the second DataTable represents the Movies database table. A parent/child relationship is created between the two DataTable objects with the help of a DataRelation. The DataRelation is used to get the movies that match each movie category. The DataRow.GetChildRows() method is called to retrieve the movies that match a particular movie category. Executing Asynchronous Database Commands Normally, when you execute a database command, the thread executing the command must wait until the command finishes before executing any additional code. In other words, normally, when you execute a database command, the thread is blocked. When you take advantage of asynchronous commands, on the other hand, the database command is executed on another thread so that the current thread can continue perform- ing other work. For example, you can use the current thread to execute yet another data- base command. There are two reasons that you might want to use asynchronous database commands when building an ASP.NET page. First, executing multiple database commands simultane- ously can significantly improve your application’s performance. This is especially true when the database commands are executed against different database servers. Second, the ASP.NET Framework uses a limited thread pool to service page requests. When ASP.NET Framework receives a request for a page, it assigns a thread to handle the request. If ASP.NET Framework runs out of threads, the request is queued until a thread becomes available. If too many threads are queued, the framework rejects the page request with a 503—Server Too Busy response code. From the Library of Wow! eBook ptg 912 CHAPTER 19 Building Data Access Components with ADO.NET If you execute a database command asynchronously, the current thread is released back into the thread pool so that it can be used to service another page request. While the asynchronous database command is executing, ASP.NET Framework can devote its atten- tion to handling other page requests. When the asynchronous command completes, the framework reassigns a thread to the original request and the page finishes executing. NOTE You can configure the ASP.NET thread pool with the httpRuntime element in the web configuration file. You can modify the appRequestQueueLimit, minFreeThreads, and minLocalRequestFreeThreads attributes to control how many requests ASP.NET Framework queues before giving up and sending an error. There are two parts to this task undertaken in this section. A data access component that supports asynchronous ADO.NET methods must be created and an ASP.NET page that executes asynchronously. Using Asynchronous ADO.NET Methods There are asynchronous versions of several ADO.NET methods. These methods come in pairs: a Begin and End method. For example, the SqlCommand object supports the following asynchronous methods: . BeginExecuteNonQuery() . EndExecuteNonQuery() . BeginExecuteReader() . EndExecuteReader() . BeginExecuteXmlReader() . EndExecuteXmlReader() The idea is that when you execute the Begin method, the asynchronous task is started on a separate thread. When the method finishes executing, you can use the End method to get the results. To use these asynchronous methods, you must use a special attribute in your connection string: the Asynchronous Processing=true attribute. The data access component in Listing 19.34 contains a BeginGetMovies() and EndGetMovies() method that fetches movies from the Movies database table asynchro- nously. These methods use the ADO.NET BeginExecuteReader() and EndExecuteReader() to fetch a DataReader asynchronously. From the Library of Wow! eBook ptg 913 Executing Asynchronous Database Commands 19 LISTING 19.34 App_Code\AsyncDataLayer.cs using System; using System.Data; using System.Data.SqlClient; using System.Web.Configuration; using System.Collections.Generic; public class AsyncDataLayer { private static readonly string _connectionString; private SqlCommand _cmdMovies; public IAsyncResult BeginGetMovies(AsyncCallback callback, Object state) { SqlConnection con = new SqlConnection(_connectionString); _cmdMovies = new SqlCommand( “WAITFOR DELAY ‘0:0:01’;SELECT Title,Director FROM Movies”, con); con.Open(); return _cmdMovies.BeginExecuteReader(callback, state, CommandBehavior.CloseConnection); } public List<AsyncDataLayer.Movie> EndGetMovies(IAsyncResult result) { List<AsyncDataLayer.Movie> results = new List<AsyncDataLayer.Movie>(); SqlDataReader reader = _cmdMovies.EndExecuteReader(result); while (reader.Read()) { AsyncDataLayer.Movie newMovie = new AsyncDataLayer.Movie(); newMovie.Title = (string)reader[“Title”]; newMovie.Director = (string)reader[“Director”]; results.Add(newMovie); } return results; } static AsyncDataLayer() { _connectionString = WebConfigurationManager.ConnectionStrings[“Movies”].ConnectionString + “;Asynchronous Processing=true”; } public class Movie { From the Library of Wow! eBook . servers. Second, the ASP. NET Framework uses a limited thread pool to service page requests. When ASP. NET Framework receives a request for a page, it assigns a thread to handle the request. If ASP. NET Framework. commands when building an ASP. NET page. First, executing multiple database commands simultane- ously can significantly improve your application’s performance. This is especially true when the. ptg 9 04 CHAPTER 19 Building Data Access Components with ADO .NET LISTING 19.31 ShowMovie9.aspx <%@ Page Language=”C#” %> <%@ Import Namespace=”System.Data” %> <!DOCTYPE html