Tài liệu Adding, Modifying, and Removing DataRowView Objects from a DataView docx

Adding, Modifying, and Removing DataRowView Objects from a DataView It's important to understand that DataRowView objects in a DataView provide access to the underlying DataRow objects i

Adding, Modifying, and Removing DataRowView Objects from a DataView

It's important to understand that DataRowView objects in a DataView provide access to the underlying DataRow objects in a DataTable Therefore, when you examine and edit the contents of a DataRowView, you're actually working with the underlying DataRow Similarly, when you remove a DataRowView, you are removing the underlying

DataRow

Adding a DataRowView to a DataView

To add a new DataRowView to a DataView, you call the AddNew() method of your DataView The AddNew() method returns a DataRowView object that you use to set the column values for the new row.The following example calls the AddNew() method of the customersDV DataView:

DataRowView customerDRV = customersDV.AddNew();

customerDRV["CustomerID"] = "J7COM";

customerDRV["CompanyName"] = "J7 Company";

customerDRV["Country"] = "UK";

customerDRV.EndEdit();

Notice the use of the EndEdit() method of the customerDRV DataRowView to end the editing The EndEdit() method creates a new DataRow in the underlying DataTable The DataColumn objects in the new DataRow will contain the column values specified in the previous code

Note You can undo the addition by calling the CancelEdit() method of a DataRowView.

You can get the underlying DataRow added to the DataTable using the Row property of a DataRowView For example:

DataRow customerDR = customerDRV.Row;

Modifying an Existing DataRowView

To begin modifying an existing DataRowView in a DataView, you call the BeginEdit() method of the DataRowView in your DataView The following example calls the

BeginEdit() method for the first DataRowView in customersDV:

customersDV[0].BeginEdit();

Note Remember that DataRowView objects in a DataView start at index 0, and therefore

customersDV[0] is the first DataRowView in customersDV

You can then modify a DataColumn in the underlying DataRow through the

DataRowView The following example sets the CompanyName DataColumn to Widgets Inc.:

customersDV[0]["CompanyName"] = "Widgets Inc.";

Once you've finished making your modifications, you call the EndEdit() method to make your modifications permanent in the underlying DataTable For example:

customersDV[0].EndEdit();

Note You can undo the modification by calling the CancelEdit() method of a

DataRowView

Removing an Existing DataRowView

To remove an existing DataRowView from a DataView, you can call the Delete() method

of either the DataView or the DataRowView When calling the Delete() method of a DataView, you pass the index of the DataRowView you want to remove The following example removes the second DataRowView from customersDV:

customersDV.Delete(1);

When calling the Delete() method of a DataRowView, you simply call that method of the DataRowView in your DataView The following example removes the third

DataRowView from customersDV:

customersDV[2].Delete();

With either of these Delete() methods, the deletion isn't committed in the underlying DataTable until you call the AcceptChanges() method of your DataTable For example: customersDT.AcceptChanges();

Note You can call the RejectChanges() method of a DataTable to undo the deletions

This method will also undo any uncommitted additions and modifications of rows

from a DataView This program also displays the IsNew and IsEdit properties of the DataRowView objects, which indicate whether the DataRowView is new and is being edited

Listing 13.3: ADDMODIFYANDREMOVEDATAROWVIEWS.CS /*

AddModifyAndRemoveDataRowViews.cs illustrates how to

add, modify, and remove DataRowView objects from a DataView

*/

using System;

using System.Data;

using System.Data.SqlClient;

class AddModifyAndRemoveDataRowViews

{

public static void DisplayDataRow(

DataRow myDataRow,

DataTable myDataTable

)

{

Console.WriteLine("\nIn DisplayDataRow()");

foreach (DataColumn myDataColumn in myDataTable.Columns) {

Console.WriteLine(myDataColumn + "= " +

myDataRow[myDataColumn]);

}

}

public static void Main()

{

SqlConnection mySqlConnection =

new SqlConnection(

"server=localhost;database=Northwind;uid=sa;pwd=sa"

);

SqlCommand mySqlCommand = mySqlConnection.CreateCommand(); mySqlCommand.CommandText =

"SELECT CustomerID, CompanyName, Country " +

"FROM Customers";

SqlDataAdapter mySqlDataAdapter = new SqlDataAdapter();

mySqlDataAdapter.SelectCommand = mySqlCommand;

DataSet myDataSet = new DataSet();

mySqlConnection.Open();

mySqlDataAdapter.Fill(myDataSet, "Customers");

mySqlConnection.Close();

DataTable customersDT = myDataSet.Tables["Customers"];

// set up the filter expression

string filterExpression = "Country = 'UK'";

// create a DataView object named customersDV

DataView customersDV = new DataView();

customersDV.Table = customersDT;

customersDV.RowFilter = filterExpression;

// add a new DataRowView (adds a DataRow to the DataTable)

Console.WriteLine("\nCalling customersDV.AddNew()");

DataRowView customerDRV = customersDV.AddNew();

customerDRV["CustomerID"] = "J7COM";

customerDRV["CompanyName"] = "J7 Company";

customerDRV["Country"] = "UK";

Console.WriteLine("customerDRV[\" CustomerID\"] = " +

customerDRV["CustomerID"]);

Console.WriteLine("customerDRV[\" CompanyName\"] = " +

customerDRV["CompanyName"]);

Console.WriteLine("customerDRV[\" Country\"] = " +

customerDRV["Country"]);

Console.WriteLine("customerDRV.IsNew = " + customerDRV.IsNew);

Console.WriteLine("customerDRV.IsEdit = " + customerDRV.IsEdit);

customerDRV.EndEdit();

// get and display the underlying DataRow

DataRow customerDR = customerDRV.Row;

DisplayDataRow(customerDR, customersDT);

// modify the CompanyName of customerDRV

Console.WriteLine("\nSetting customersDV[0][\" CompanyName\"] to Widgets Inc."); customersDV[0].BeginEdit();

customersDV[0]["CompanyName"] = "Widgets Inc.";

Console.WriteLine("customersDV[0][\" CustomerID\"] = " +

customersDV[0]["CustomerID"]);

Console.WriteLine("customersDV[0][\" CompanyName\"] = " +

customersDV[0]["CompanyName"]);

Console.WriteLine("customersDV[0].IsNew = " + customersDV[0].IsNew);

Console.WriteLine("customersDV[0].IsEdit = " + customersDV[0].IsEdit);

customersDV[0].EndEdit();

// display the underlying DataRow

DisplayDataRow(customersDV[0].Row, customersDT);

// remove the second DataRowView from customersDV

Console.WriteLine("\ncustomersDV[1][\" CustomerID\"] = " +

customersDV[1]["CustomerID"]);

Console.WriteLine("\nCalling customersDV.Delete(1)");

customersDV.Delete(1);

Console.WriteLine("customersDV[1].IsNew = " + customersDV[1].IsNew); Console.WriteLine("customersDV[1].IsEdit = " + customersDV[1].IsEdit);

// remove the third DataRowView from customersDV

Console.WriteLine("\ncustomersDV[2][\" CustomerID\"] = " +

customersDV[2]["CustomerID"]);

Console.WriteLine("\nCalling customersDV[2].Delete()");

customersDV[2].Delete();

// call the AcceptChanges() method of customersDT to

// make the deletes permanent in customersDT

customersDT.AcceptChanges();

// display the rows in the customersDV DataView object

Console.WriteLine("\nDataRowView objects in customersDV:\n");

foreach (DataRowView myDataRowView in customersDV)

{

for (int count = 0; count < customersDV.Table.Columns.Count; count++) {

Console.WriteLine(myDataRowView[count]);

}

Console.WriteLine("");

}

}

}

The output from this program is as follows:

Calling customersDV.AddNew()

customerDRV["CustomerID"] = J7COM

customerDRV["CompanyName"] = J7 Company

customerDRV["Country"] = UK

customerDRV.IsNew = True

customerDRV.IsEdit = True

In DisplayDataRow()

CustomerID = J7COM

CompanyName = J7 Company

Country = UK

Setting customersDV[0]["CompanyName"] to Widgets Inc customersDV[0]["CustomerID"] = AROUT

customersDV[0]["CompanyName"] = Widgets Inc

customersDV[0].IsNew = False

customersDV[0].IsEdit = True

In DisplayDataRow()

CustomerID = AROUT

CompanyName = Widgets Inc

Country = UK

customersDV[1]["CustomerID"] = BSBEV

Calling customersDV.Delete(1)

customersDV[1].IsNew = False

customersDV[1].IsEdit = False

customersDV[2]["CustomerID"] = EASTC

Calling customersDV[2].Delete()

DataRowView objects in customersDV:

AROUT

Widgets Inc

UK

CONSH

Consolidated Holdings

UK

ISLAT

Island Trading

UK

NORTS

North/South

UK

SEVES

Seven Seas Imports

UK

J7COM J7 Company

UK