concurrency-rowupdated.aspx
来自「东软内部材料（四）asp等相关的教学案例 」· ASPX 代码 · 共 324 行
ASPX
324 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>Managing Concurrent Updates with the RowUpdated Event</title>
<!-- #include file="..\global\style.inc" -->
</head>
<body bgcolor="#ffffff">
<span class="heading">Managing Concurrent Updates with the RowUpdated Event</span><hr />
<!--------------------------------------------------------------------------->
<%// -- insert connection string script --%>
<wrox:connect id="ctlConnectStrings" runat="server"/>
<div id="outError" runat="server"> </div>
<b>Initial contents of the Books table:</b>
<asp:datagrid id="dgrResult1" runat="server" /><p />
<b>Contents of the Books table after editing:</b>
<asp:datagrid id="dgrResult2" runat="server" /><p />
<div id="outConcurrent" runat="server"></div><p />
<div id="outResult" runat="server"></div><p />
<b>Contents of the Errors table in a new DataSet after updating:</b>
<asp:datagrid id="dgrResult3" runat="server" /><p />
<b>Note:</b> while this page does execute the Update method of the DataSet, it does not<br />
actually change the original data. It uses a transaction that is rolled back afterwards.</br />
Otherwise, the update would prevent the code from running the next time.
<script language="C#" runat="server">
string gstrResult; // to hold the result messages
string gstrConnect; // to hold connection string
DataSet gobjDataSet; // to hold rows from database
DataTable gobjErrorTable; // to hold a list of errors
DataSet gobjErrorDS; // to hold the Errors table
void Page_Load(Object sender, EventArgs e)
{
// get connection string from ..\global\connect-strings.ascx user control
gstrConnect = ctlConnectStrings.OLEDBConnectionString;
// specify the SELECT statement to extract the data
string strSelect = "SELECT * FROM BookList WHERE ISBN LIKE '18610022%'";
// create a new DataSet object
gobjDataSet = new DataSet();
// create a new Connection object using the connection string
OleDbConnection objConnect = new OleDbConnection(gstrConnect);
// create a new DataAdapter using the connection object and select statement
OleDbDataAdapter objDataAdapter = new OleDbDataAdapter(strSelect, objConnect);
try
{
// fill the dataset with data using the DataAdapter object
objDataAdapter.Fill(gobjDataSet, "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
gobjDataSet.AcceptChanges();
// declare a variable to reference the Books table
DataTable objTable = gobjDataSet.Tables["Books"];
// display the contents of the Books table before changing data
dgrResult1.DataSource = objTable.DefaultView;
dgrResult1.DataBind(); // and bind (display) the data
// now change some records in the Books table
objTable.Rows[0].Delete();
objTable.Rows[1]["Title"] = "Amateur Theatricals for Windows 2000";
objTable.Rows[2].Delete();
objTable.Rows[3].Delete();
objTable.Rows[4]["PublicationDate"] = "01-01-2002";
objTable.Rows.RemoveAt(5);
// notice that using the Remove method on row 5 (rather than marking
// it as deleted) means that the next row then becomes row 5
objTable.Rows[5]["ISBN"] = "200000000";
// add a new row using an array of values
Object[] objValsArray = new Object[3];
objValsArray[0] = "200000001";
objValsArray[1] = "Impressionist Guide to Painting Computers";
objValsArray[2] = "05-02-2002";
objTable.Rows.Add(objValsArray);
// display the contents of the Books table after changing the data
dgrResult2.DataSource = objTable.DefaultView;
dgrResult2.DataBind(); // and bind (display) the data
//-------------------------------------------------------------------
// change some values in the original table while the DataSet is holding
// a disconnected copy of the data to force a concurrency error
string strConcurrent = String.Empty;
string strUpdate = String.Empty;
int intRowsAffected;
// need a new (separate) Connection and Command object
OleDbConnection objnewConnect = new OleDbConnection(gstrConnect);
OleDbCommand objnewCommand = new OleDbCommand();
objnewCommand.Connection = objnewConnect;
try
{
objnewConnect.Open();
// modify two of the book titles to force concurrency errors
strConcurrent += "<b>Concurrently executed</b>:<br />";
DateTime datNow = DateTime.Now;
string strNow = datNow.ToString("dd-M-yy \\a\\t hh:mm:ss");
strUpdate = "UPDATE BookList SET Title = 'new Book Written on "
+ strNow + "' WHERE ISBN = '186100222X'";
objnewCommand.CommandText = strUpdate;
intRowsAffected = objnewCommand.ExecuteNonQuery();
strConcurrent += strUpdate + "<br /> ... <b>"
+ intRowsAffected.ToString() + "</b> row(s) affected<br />";
// edit the next line to force a concurrency error if none occurs
strUpdate = "UPDATE BookList SET Title = 'Another Book Written on "
+ strNow + "' WHERE ISBN = '1861002262'";
objnewCommand.CommandText = strUpdate;
intRowsAffected = objnewCommand.ExecuteNonQuery();
strConcurrent += strUpdate + "<br /> ... <b>"
+ intRowsAffected.ToString() + "</b> row(s) affected<br />";
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 = strConcurrent;
//----------------------------------------------------------------
// now set up event handler to react to RowUpdated event
objDataAdapter.RowUpdated += new OleDbRowUpdatedEventHandler(OnRowUpdated);
//----------------------------------------------------------------
// create a new empty Table object to hold error rows
gobjErrorTable = new DataTable("Errors");
// define the columns for the Errors table
gobjErrorTable.Columns.Add("Action", System.Type.GetType("System.String"));
gobjErrorTable.Columns.Add("RowKey", System.Type.GetType("System.String"));
gobjErrorTable.Columns.Add("ColumnName", System.Type.GetType("System.String"));
gobjErrorTable.Columns.Add("OriginalValue", System.Type.GetType("System.String"));
gobjErrorTable.Columns.Add("CurrentValue", System.Type.GetType("System.String"));
gobjErrorTable.Columns.Add("DatabaseValue", System.Type.GetType("System.String"));
// create a new empty DataSet object to hold Errors table
gobjErrorDS = new DataSet();
gobjErrorDS.Tables.Add(gobjErrorTable);
//----------------------------------------------------------------
// declare a variable to hold a Transaction object
OleDbTransaction objTransaction = null;
try
{
// 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, insert and delete commands for the DataAdapter
objDataAdapter.DeleteCommand = objCommandBuilder.GetDeleteCommand();
objDataAdapter.InsertCommand = objCommandBuilder.GetInsertCommand();
objDataAdapter.UpdateCommand = objCommandBuilder.GetUpdateCommand();
// start a transaction so that we can roll back the changes
// must do this on an open Connection object
objConnect.Open();
objTransaction = objConnect.BeginTransaction();
// attach the current transaction to all the Command objects
// must be done after setting Connection property
objDataAdapter.DeleteCommand.Transaction = objTransaction;
objDataAdapter.InsertCommand.Transaction = objTransaction;
objDataAdapter.UpdateCommand.Transaction = objTransaction;
// perform the update on the original data
objDataAdapter.Update(gobjDataSet, "Books");
}
catch (Exception objError)
{
// rollback the transaction undoing any updates
objTransaction.Rollback();
// display error details
outError.InnerHtml = "<b>* Error while updating original data</b>.<br />"
+ objError.Message + "<br />" + objError.Source;
return; // and stop execution
}
// to actually update the source tables just change the next line
// to CommitTransaction() or remove the transaction altogether.
// note that you will then have to change the SELECT statement and
// code to be able to run the example again, or rebuild the
// original data from the supplied SQL scripts
objTransaction.Rollback();
// display the results of the Update
outResult.InnerHtml = gstrResult;
// display the contents of the Errors table
dgrResult3.DataSource = gobjErrorDS;
dgrResult3.DataMember = "Errors";
dgrResult3.DataBind(); // and bind (display) the data
}
//----------------------------------------------------------------
// event handler for the RowUpdated event
void OnRowUpdated(Object objSender, OleDbRowUpdatedEventArgs objArgs)
{
// see if the update was successful
if (objArgs.RecordsAffected < 1)
{
// get the text description of the StatementType
string strType = System.Enum.GetName(objArgs.StatementType.GetType(), objArgs.StatementType);
// get the primary key of the row (the ISBN)
string strRowKey = objArgs.Row["ISBN", DataRowVersion.Original].ToString();
// get a reference to the original table in the DataSet
DataTable objTable = gobjDataSet.Tables[0];
string strColumnName; // to hold the column name
// iterate through the columns in the current row
foreach (DataColumn objColumn in objTable.Columns)
{
// get the column name as a string
strColumnName = objColumn.ColumnName;
// see if this column has been modified
if (objArgs.Row[strColumnName, DataRowVersion.Current]
!= objArgs.Row[strColumnName, DataRowVersion.Original])
{
// create a new DataRow object instance in this table
DataRow objDataRow = gobjErrorTable.NewRow();
// and fill in the values
objDataRow["Action"] = strType;
objDataRow["RowKey"] = strRowKey;
objDataRow["ColumnName"] = strColumnName;
objDataRow["OriginalValue"] = objArgs.Row[strColumnName, DataRowVersion.Original];
objDataRow["CurrentValue"] = objArgs.Row[strColumnName, DataRowVersion.Current];
objDataRow["DatabaseValue"] = GetCurrentColumnValue(gstrConnect, strRowKey, strColumnName);
// add new row to the Errors table
gobjErrorTable.Rows.Add(objDataRow);
}
}
// set the Status property of the row to skip current row update if there is an error
// default is Continue which means an error will halt execution of following updates
objArgs.Status = UpdateStatus.SkipCurrentRow;
}
}
//----------------------------------------------------------------
string GetCurrentColumnValue(string strConnect, string strISBN, string strColumnName)
{
// select the existing column value from the underlying table in the database
string strSQL = "SELECT " + strColumnName
+ " FROM BookList WHERE ISBN='" + strISBN + "'";
string CurrVal = String.Empty;
OleDbConnection objConnect = new OleDbConnection(strConnect);
OleDbCommand objCommand = new OleDbCommand(strSQL, objConnect);
try
{
objConnect.Open();
// use ExecuteScalar for efficiency, it returns only one item
// get the value direct from it and convert to a String
CurrVal = objCommand.ExecuteScalar().ToString();
objConnect.Close();
}
catch (Exception objError)
{
CurrVal = "*Error*";
}
return CurrVal;
}
</script>
<!--------------------------------------------------------------------------->
<!-- #include file="..\global\foot.inc" -->
</body>
</html>
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