Adding, Modifying, and Removing DataRowView Objects from a DataView

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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.

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Nội dung Text: Adding, Modifying, and Removing DataRowView Objects from a DataView

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. Listing 13.3 shows a program that adds, modifies, and removes DataRowView objects 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