ASP.NET 4 Unleased - p 93 potx

void Page_Load { // Create connection string connectionString = WebConfigurationManager.ConnectionStrings[“Movies”].ConnectionString; SqlConnection con = new SqlConnectionconnectionStrin

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void Page_Load()

{

// Create connection

string connectionString =

WebConfigurationManager.ConnectionStrings[“Movies”].ConnectionString;

SqlConnection con = new SqlConnection(connectionString);

// Create Select command

dad = new SqlDataAdapter(“SELECT Id,Title,Director FROM Movies”, con);

// Create Update, Insert, and Delete commands with SqlCommandBuilder

SqlCommandBuilder builder = new SqlCommandBuilder(dad);

// Add data to DataTable

dtblMovies = new DataTable();

dad.Fill(dtblMovies);

// Bind data to Repeater

rptMovies.DataSource = dtblMovies;

rptMovies.DataBind();

}

protected void lnkUpdate_Click(object sender, EventArgs e)

{

// Update DataTable with changes

for (int i=0; i < rptMovies.Items.Count;i++)

{

RepeaterItem item = rptMovies.Items[i];

TextBox txtTitle = (TextBox)item.FindControl(“txtTitle”);

TextBox txtDirector = (TextBox)item.FindControl(“txtDirector”);

if (dtblMovies.Rows[i][“Title”] != txtTitle.Text)

dtblMovies.Rows[i][“Title”] = txtTitle.Text;

if (dtblMovies.Rows[i][“Director”] != txtDirector.Text)

dtblMovies.Rows[i][“Director”] = txtDirector.Text;

}

// Set batch size to maximum size

dad.UpdateBatchSize = 0;

// Perform update

int numUpdated = dad.Update(dtblMovies);

lblResults.Text = String.Format(“Updated {0} rows”, numUpdated);

}

</script>

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<title>Show DataAdapter Update</title>

</head>

<body>

<div>

<asp:Repeater

id=”rptMovies”

EnableViewState=”false”

Runat=”server”>

<table>

<tr>

<th>Title</th><th>Director</th>

</tr>

</HeaderTemplate>

<tr>

<td>

<asp:TextBox

id=”txtTitle”

Text=’<%#Eval(“Title”)%>’

Runat=”server” />

</td>

<td>

<asp:TextBox

id=”txtDirector”

Text=’<%#Eval(“Director”)%>’

</td>

</tr>

</ItemTemplate>

</table>

</FooterTemplate>

</asp:Repeater>

<br />

<asp:LinkButton

id=”lnkUpdate”

Text=”Update Movies”

Runat=”server” OnClick=”lnkUpdate_Click” />

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<asp:Label

id=”lblResults”

EnableViewState=”false”

</div>

</form>

</body>

</html>

The SqlDataAdapter in Listing 19.27 performs a batch update When a SqlDataAdapter

object’s UpdateBatchSize property is set to the value 0, the SqlDataAdapter performs all

its updates in a single batch If you want to perform updates in smaller batches, you can

set the UpdateBatchSize to a particular size

Using the DataTable Object

The DataTable object represents an in-memory database table You can add rows to a

DataTable with a SqlDataAdapter, with a SqlDataReader, with an XML file, or

program-matically For example, the page in Listing 19.28 builds a new DataTable

programmati-cally The contents of the DataTable then display in a GridView control (see Figure 19.14)

FIGURE 19.14 Displaying a DataTable that was built programmatically

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LISTING 19.28 ShowDataTableProgram.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”>

void Page_Load()

{

// Create the DataTable columns

DataTable newDataTable = new DataTable();

newDataTable.Columns.Add(“Id”, typeof(int));

newDataTable.Columns.Add(“ProductName”, typeof(string));

newDataTable.Columns.Add(“ProductPrice”, typeof(decimal));

// Mark the Id column as an autoincrement column

newDataTable.Columns[“Id”].AutoIncrement = true;

// Add some data rows

for (int i = 1; i < 11; i++)

{

DataRow newRow = newDataTable.NewRow();

newRow[“ProductName”] = “Product “ + i.ToString();

newRow[“ProductPrice”] = 12.34m;

newDataTable.Rows.Add(newRow);

}

// Bind DataTable to GridView

grdProducts.DataSource = newDataTable;

grdProducts.DataBind();

}

</script>

<title>Show DataTable Programmatically</title>

</head>

<body>

<div>

<h1>Products</h1>

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<asp:GridView

id=”grdProducts”

</div>

</form>

</body>

</html>

In Listing 19.28, a DataTable with the following three columns is created: Id,

ProductName, and ProductPrice The data type of each column is specified with a NET

Framework type For example, the ProductPrice column is created as a decimal column

Alternatively, you could create each column with a SqlType For example, you could use

System.Data.SqlTypes.SqlDecimal for the type of the ProductPrice column

The Id column is created as an autoincrement column When you add new rows to the

DataTable, the column increments its value automatically

Selecting DataRows

You can retrieve particular rows from a DataTable by using the DataTable object’s

Select() method The Select() method accepts a filter parameter You can use just about

anything that you would use in a SQL WHERE clause with the filter parameter

When you retrieve an array of rows with the Select() method, you can also specify a sort

order for the rows When specifying a sort order, you can use any expression that you

would use with a SQL ORDER BY clause

For example, the page in Listing 19.29 caches a DataTable in memory with the ASP.NET

Cache object The page contains a TextBox control When you enter a partial movie title

into the TextBox control, a list of matching movies is displayed in a GridView control The

rows are sorted in order of the movie title (see Figure 19.15)

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LISTING 19.29 ShowDataTableSelect.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”>

protected void btnSearch_Click(object sender, EventArgs e)

{

// Get movies DataTable from Cache

DataTable dtblMovies = (DataTable)Cache[“MoviesToFilter”];

if (dtblMovies == null)

{

dtblMovies = GetMoviesFromDB();

Cache[“MoviesToFilter”] = dtblMovies;

}

// Select matching rows

string filter = String.Format(“Title LIKE ‘{0}*’”, txtTitle.Text);

DataRow[] rows = dtblMovies.Select(filter, “Title”);

FIGURE 19.15 Selecting matching rows from a cached DataTable

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// Bind to GridView

grdMovies.DataSource = rows;

grdMovies.DataBind();

}

private DataTable GetMoviesFromDB()

{

SqlDataAdapter dad = new SqlDataAdapter(

“SELECT Title, Director FROM Movies”, connectionString);

DataTable dtblMovies = new DataTable();

return dtblMovies;

}

</script>

th, td

{

padding:5px;

}

</style>

<title>Show DataTable Select</title>

</head>

<body>

<div>

<asp:TextBox

id=”txtTitle”

Tooltip=”Search”

<asp:Button

id=”btnSearch”

Text=”Search”

Runat=”server” OnClick=”btnSearch_Click” />

<hr />

<asp:GridView

id=”grdMovies”

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Runat=”server”>

<asp:TemplateField HeaderText=”Title”>

<%# ((DataRow)Container.DataItem)[“Title”] %>

</ItemTemplate>

</asp:TemplateField>

<asp:TemplateField HeaderText=”Director”>

<%# ((DataRow)Container.DataItem)[“Director”] %>

</ItemTemplate>

</asp:TemplateField>

</Columns>

</asp:GridView>

</div>

</form>

</body>

</html>

The DataTable Select() method returns an array of DataRow objects There is nothing

wrong with binding an array of DataRow objects to a GridView control However, you

must explicitly cast each data item to a DataRow and read within a GridView

TemplateField

DataRow States and DataRow Versions

When you modify the rows in a DataTable, the DataTable keeps track of the changes that

you make A DataTable maintains both the original and modified version of each row

Each row in a DataTable has a particular RowState that has one of the following values:

Unchanged—The row has not been changed

Added—The row has been added

Modified—The row has been modified

Deleted—The row has been deleted

Detached—The row has been created but not added to the DataTable

Each row in a DataTable can have more than one version Each version is represented by

one of the following values of the DataRowVersion enumeration:

Current—The current version of the row

Default—The default version of the row

Original—The original version of the row

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You can use the DataTable.AcceptChanges() method to copy the current versions of all

the rows to the original versions of all the rows And you can use the

DataTable.RejectChanges() method to copy the original versions of all the rows to the

current versions of all the rows

For example, the component in Listing 19.30 includes an AcceptChanges() and

RejectChanges() method The component maintains a DataTable in Session state If you

update a row in the DataTable, the row is updated in memory If the RejectChanges()

method is called, any changes made to the DataTable are rejected If the AcceptChanges()

method is called, the database is updated and all changes are accepted

LISTING 19.30 App_Code\Movie9.cs

using System;

using System.Data;

using System.Data.SqlClient;

using System.Web;

using System.Web.Configuration;

public class Movie9

{

private SqlDataAdapter dad = new SqlDataAdapter();

public DataTable GetAll()

{

return (DataTable)HttpContext.Current.Session[“MoviesToEdit”];

}

public void Update(int id, string title, string director)

{

DataTable movies = (DataTable)HttpContext.Current.Session[“MoviestoEdit”];

DataRow rowToEdit = movies.Rows.Find(id);

rowToEdit[“title”] = title;

rowToEdit[“director”] = director;

}

public void RejectChanges()

{

movies.RejectChanges();

}

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public void AcceptChanges()

{

dad.Update(movies);

movies.AcceptChanges();

}

public Movie9()

{

// Create Data Adapter

dad = new SqlDataAdapter(

“SELECT Id,Title,Director FROM Movies”, connectionString);

SqlCommandBuilder builder = new SqlCommandBuilder(dad);

dad.UpdateBatchSize = 0;

HttpContext context = HttpContext.Current;

if (context.Session[“MoviesToEdit”] == null)

{

// Add data to DataTable

DataTable dtblMovies = new DataTable();

dtblMovies.PrimaryKey = new DataColumn[] { dtblMovies.Columns[“Id”] };

context.Session[“MoviesToEdit”] = dtblMovies;

}

The page in Listing 19.31 contains a GridView that is bound to the component in Listing

19.30 The GridView includes a column that indicates whether each row has been

changed The column displays the value of the corresponding DataRow object’s RowState

property (see Figure 19.16)

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