concurrency-error.aspx
来自「Professional ASP.NET source code」· ASPX 代码 · 共 166 行
ASPX
166 行
<%@Page Language="C#"%>
<%@Import Namespace="System.Data" %>
<%@Import Namespace="System.Data.OleDb" %>
<%@ Register TagPrefix="wrox" TagName="connect" Src="..\global\connect-strings.ascx" %>
<!DOCTYPE HTML PUBLIC "-// W3C// DTD HTML 4.0 Transitional// EN">
<html><head>
<title>Catching Concurrency Errors When Updating the Source Data</title>
<!-- #include file="..\global\style.inc" -->
</head>
<body bgcolor="#ffffff">
<span class="heading">Catching Concurrency Errors When Updating the Source Data</span><hr />
<!--------------------------------------------------------------------------->
<%// -- insert connection string script --%>
<wrox:connect id="ctlConnectStrings" runat="server"/>
<div>Connection string: <b><span id="outConnect" runat="server"></span></b></div>
<div>SELECT command: <b><span id="outSelect" runat="server"></span></b></div>
<div>UPDATE command: <b><span id="outUpdate" runat="server"></span></b></div><p />
<b>Initial contents of the Books table:</b>
<asp:datagrid id="dgrResult1" runat="server" /><p />
<b><div id="outConcurrent" runat="server"></div></b><p />
<b>Contents of the Books table after editing:</b>
<asp:datagrid id="dgrResult2" runat="server" /><p />
<div id="outResult" runat="server"></div><p />
<div id="outError" runat="server"></div><p />
<script language="C#" runat="server">
void Page_Load(Object sender, EventArgs e)
{
// get connection string from ..\global\connect-strings.ascx user control
string strConnect = ctlConnectStrings.OLEDBConnectionString;
outConnect.InnerText = strConnect;
// specify the SELECT statement to extract the data
string strSelect = "SELECT * FROM BookList WHERE ISBN='1861001622'";
outSelect.InnerText = strSelect; // and display it
// create a new DataSet object
DataSet objDataSet = new DataSet();
// create a new Connection object using the connection string
OleDbConnection objConnect = new OleDbConnection(strConnect);
// create a new DataAdapter using the connection object and select statement
OleDbDataAdapter objDataAdapter = new OleDbDataAdapter(strSelect, objConnect);
try
{
// fill the dataset with data from the DataAdapter object
objDataAdapter.Fill(objDataSet, "Books");
}
catch (Exception objError)
{
// display error details
outError.InnerHtml = "<b>* Error while accessing data</b>.<br />"
+ objError.Message + "<br />" + objError.Source;
return; // and stop execution
}
// accept the changes to "fix" the current state of the DataSet contents
// objDataSet.AcceptChanges();
// declare a variable to reference the Books table
DataTable objTable = objDataSet.Tables["Books"];
// display the contents of the Books table before changing data
dgrResult1.DataSource = objTable.DefaultView;
dgrResult1.DataBind(); // and bind (display) the data
//-------------------------------------------------------------------
// change a value in the original table while the DataSet is holding
// a disconnected copy of the data to force a concurrency error
string strUpdate;
DateTime datNow = DateTime.Now;
string strNow = datNow.ToString("dd-M-yy \\a\\t hh:mm:ss");
strUpdate = "UPDATE BookList SET Title = 'Book Written on "
+ strNow + "' WHERE ISBN = '1861001622'";
int intRowsAffected;
OleDbConnection objnewConnect = new OleDbConnection(strConnect);
OleDbCommand objnewCommand = new OleDbCommand(strUpdate, objnewConnect);
try
{
// open the connection to the database
objnewConnect.Open();
// execute the SQL statement and return the number of rows affected
intRowsAffected = objnewCommand.ExecuteNonQuery();
objnewConnect.Close();
}
catch (Exception objError)
{
// display error details
outError.InnerHtml = "<b>* Error while updating original data</b>.<br />"
+ objError.Message + "<br />" + objError.Source;
return; // and stop execution
}
outConcurrent.InnerHtml = "Command object concurrently updated "
+ intRowsAffected.ToString() + " record(s)<br />" + strUpdate;
//-------------------------------------------------------------------
// now change the record in the Books table
objTable.Rows[0]["Title"] = "Amateur Theatricals for Windows 2000";
objTable.Rows[0]["PublicationDate"] = DateTime.Now;
// display the contents of the Books table after changing the data
dgrResult2.DataSource = objTable.DefaultView;
dgrResult2.DataBind(); // and bind (display) the data
try
{
// perform the update on the original data
// create an auto-generated command builder to create the commands
// to update, insert and delete the data
OleDbCommandBuilder objCommandBuilder = new OleDbCommandBuilder(objDataAdapter);
// set the update command for the DataAdapter
//(we don// t need insert and delete commands in this example)
objDataAdapter.UpdateCommand = objCommandBuilder.GetUpdateCommand();
//*******************************************************************
// To suppress errors, uncomment next code line. It prevents exceptions
// being thrown, and allows the updates to continue on any other rows.
// The error details can then be obtained from the RowError property
// of the row that generated the error if required (see later).
// objDataAdapter.ContinueUpdateOnError = true;
//*******************************************************************
// display the auto-generated UPDATE command statement
outUpdate.InnerText = objDataAdapter.UpdateCommand.CommandText;
// now do the update
intRowsAffected = objDataAdapter.Update(objDataSet, "Books");
outResult.InnerHtml = "<b>* DataSet.Update</b> affected <b>"
+ intRowsAffected.ToString() + "</b> row(s).<p />"
+ "Value of <b>RowError</b> property for the modified row is:<br />"
+ "<b>" + objDataSet.Tables[0].Rows[0].RowError + "</b>.";
}
catch (Exception objError)
{
// display error details
outError.InnerHtml = "<b>* Error while updating original data</b>.<br />"
+ objError.Message + "<br />" + objError.Source;
}
}
</script>
<!--------------------------------------------------------------------------->
<!-- #include file="..\global\foot.inc" -->
</body>
</html>
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