Tài liệu Accessing Deleted Rows in a DataTable pptx

When AcceptChanges is called on the DataSet, DataTable, or DataRow, either explicitly or implicitly by calling the Update method of the DataAdapter, the following occurs: • All rows w

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Recipe 2.6 Accessing Deleted Rows in a DataTable

Problem

When you delete rows from a DataSet they are really marked for deletion until changes are committed by calling AcceptChanges( ) either directly or indirectly You want to access the rows that you have deleted from a DataTable

Solution

Use either a DataView or the Select( ) method of the DataTable to access deleted rows The sample code contains three event handlers:

Form.Load

Sets up the sample by creating a DataTable containing Orders data from

Northwind A view containing the Current rows is bound to a data grid on the form

Current Rows RadioButton.CheckedChanged

Sets the view of the Orders data to display only Current rows The text box

displaying information about deleted rows is cleared

Deleted Rows RadioButton.CheckedChanged

Sets the view of the Orders data to display only Deleted rows The DataTable for the DataView is retrieved and the Select( ) method is used to get the Deleted rows The overloaded indexer in C#, or Item( ) property in VB.NET, is used to retrieve the OrderID from the Original version of these deleted rows This information is displayed in the text box on the form

The C# code is shown in Example 2-6

Example 2-6 File: AccessDeletedRowsForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Text;

using System.Data;

using System.Data.SqlClient;

private DataView dv;

//

private void AccessDataSetDeletedRowsForm_Load(object sender,

System.EventArgs e)

{

// Fill the Orders table

SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM Orders", ConfigurationSettings.AppSettings["Sql_ConnectString"]);

DataTable dt = new DataTable("Orders");

da.Fill(dt);

// Define a view of just the Current rows

dv = new DataView(dt, null, null, DataViewRowState.CurrentRows); dataGrid.DataSource = dv;

currentRadioButton.Checked = true;

}

private void currentRadioButton_CheckedChanged(object sender,

System.EventArgs e)

{

// Filter to include only current rows

dv.RowStateFilter = DataViewRowState.CurrentRows;

dataGrid.ReadOnly = false;

deletedTextBox.Clear( );

}

private void deletedRadioButton_CheckedChanged(object sender,

System.EventArgs e)

{

// Filter the view to include only deleted rows

dv.RowStateFilter = DataViewRowState.Deleted;

dataGrid.ReadOnly = true;

// Get the DataTable from the DataView

DataTable dt = dv.Table;

// Filter using the DataTable RowState

DataRow[] delRows = dt.Select(null, null, DataViewRowState.Deleted);

StringBuilder sb = new StringBuilder("Deleted Records:" +

Environment.NewLine);

// Iterate over the collection of deleted rows

foreach(DataRow row in delRows)

sb.Append("Order ID: " + row["OrderID",

DataRowVersion.Original] + Environment.NewLine);

deletedTextBox.Text = sb.ToString( );

}

Discussion

ADO.NET manages the state of the rows while they are being modified Rows are

assigned a state from the DataRowState enumeration described in Table 2-4

Table 2-4 DataRowState enumeration Value Description

Added The row has been added to the collection of rows in the table but

AcceptChanges( ) has not been called

Deleted The row has been deleted from the collection of rows in the table but

AcceptChanges( ) has not been called

Detached The row does not belong to the collection of rows in a DataTable

Modified The data in the row has been changed but AcceptChanges( ) has not been

called

Unchanged The data in the row has not been changed since it was loaded or since

AcceptChanges( ) was last called

When AcceptChanges( ) is called on the DataSet, DataTable, or DataRow, either

explicitly or implicitly by calling the Update( ) method of the DataAdapter, the following occurs:

• All rows with a row state of Deleted are removed

• All other rows are assigned a row state of Unchanged and the Original row version

values are overwritten with the Current version values

When RejectChanges( ) is called on the DataSet, DataTable, or DataRow, the following

occurs:

• All rows with a row state of Added are removed

• All other rows are assigned a row state of Unchanged and the Current row version

values are overwritten with the Original row version values

Each DataRow has a RowState property that returns the current state of the row

ADO.NET maintains several versions of the data in each row while it is being modified

to allow the disconnected to be later reconciled with the data source Table 2-5 describes

the DataRowVersion enumeration values

Table 2-5 DataRowVersion enumeration Value Description

Current Current value This version does not exist for rows with a state of Deleted

Default

Default value as determined by the DataRowState:

• The Current version for rows with Added, Modified, or Unchanged state

• The Original version for rows with Deleted state

• The Proposed value for rows with Detached state

Original Original value This version does not exist for rows with a state of Added

Proposed Proposed value This value exists during a row edit operation started either

implicitly or explicitly with the BeginEdit( ) method and for Detached rows

The HasVersion( ) method of the DataRow object checks whether a particular row

version exists

The DataViewRowState enumeration is used to retrieve a particular version of data or to

determine whether a version exists It is used for this purpose by both the Select( )

method of the DataTable and by the RowStateFilter property of the DataView You can

retrieve more than one version by using a Boolean OR of DataViewRowState values

Table 2-6 describes the DataViewRowState enumeration values

Table 2-6 DataViewRowState enumeration Value Description

Added The Current version of all Added rows

CurrentRows The Current version of all Unchanged, Added, and Modified rows

This is the default value

Deleted The Original version of all Deleted rows

ModifiedCurrent The Current version of all Modified rows

ModifiedOriginal The Original version of all Modified rows

OriginalRows The Original version of Unchanged, Modified, and Deleted rows Unchanged The Current version of all Unchanged rows

The Current version of each row is retrieved by default when accessing rows in a

DataTable or in a DataView The solution demonstrates an approach for getting Deleted rows from both a DataTable and a DataView Deleted rows include only those marked for deletion using the Delete( ) method of the DataRow or the DataView, not the

Remove( ) or RemoveAt( ) method of the DataRowCollection, which instead

immediately removes the specified DataRow from the collection

The solution demonstrates two techniques for retrieving the deleted rows:

To get the Deleted rows from the DataTable, use an overload of the Select( ) method of the DataTable to return an array of deleted DataRow objects The overload accepts an argument having a DataViewRowState enumeration value To retrieve deleted rows, pass

a value of Deleted as the argument

To get the Deleted rows from the DataView, set the RowStateFilter property of the DataView to Deleted Deleted rows are also visible, along with other rows, when you set the RowStateFilter property to ModifiedOriginal and OriginalRows

[ Team LiB ]

[ Team LiB ]

Recipe 2.6 Accessing Deleted Rows in a DataTable

Problem

When you delete rows from a DataSet they are really marked for deletion until changes are committed by calling AcceptChanges( ) either directly or indirectly You want to access the rows that you have deleted from a DataTable

Solution

Use either a DataView or the Select( ) method of the DataTable to access deleted rows The sample code contains three event handlers:

Form.Load

Sets up the sample by creating a DataTable containing Orders data from

Northwind A view containing the Current rows is bound to a data grid on the form

Current Rows RadioButton.CheckedChanged

Sets the view of the Orders data to display only Current rows The text box

displaying information about deleted rows is cleared

Deleted Rows RadioButton.CheckedChanged

Sets the view of the Orders data to display only Deleted rows The DataTable for the DataView is retrieved and the Select( ) method is used to get the Deleted rows The overloaded indexer in C#, or Item( ) property in VB.NET, is used to retrieve the OrderID from the Original version of these deleted rows This information is displayed in the text box on the form

The C# code is shown in Example 2-6

Example 2-6 File: AccessDeletedRowsForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Text;

using System.Data;

using System.Data.SqlClient;

private DataView dv;

//

private void AccessDataSetDeletedRowsForm_Load(object sender,

System.EventArgs e)

{

// Fill the Orders table

SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM Orders", ConfigurationSettings.AppSettings["Sql_ConnectString"]);

DataTable dt = new DataTable("Orders");

da.Fill(dt);

// Define a view of just the Current rows

dv = new DataView(dt, null, null, DataViewRowState.CurrentRows); dataGrid.DataSource = dv;

currentRadioButton.Checked = true;

}

private void currentRadioButton_CheckedChanged(object sender,

System.EventArgs e)

{

// Filter to include only current rows

dv.RowStateFilter = DataViewRowState.CurrentRows;

dataGrid.ReadOnly = false;

deletedTextBox.Clear( );

}

private void deletedRadioButton_CheckedChanged(object sender,

System.EventArgs e)

{

// Filter the view to include only deleted rows

dv.RowStateFilter = DataViewRowState.Deleted;

dataGrid.ReadOnly = true;

// Get the DataTable from the DataView

DataTable dt = dv.Table;

// Filter using the DataTable RowState

DataRow[] delRows = dt.Select(null, null, DataViewRowState.Deleted);

StringBuilder sb = new StringBuilder("Deleted Records:" +

Environment.NewLine);

// Iterate over the collection of deleted rows

foreach(DataRow row in delRows)

sb.Append("Order ID: " + row["OrderID",

DataRowVersion.Original] + Environment.NewLine);

deletedTextBox.Text = sb.ToString( );

}

Discussion

ADO.NET manages the state of the rows while they are being modified Rows are

assigned a state from the DataRowState enumeration described in Table 2-4

Table 2-4 DataRowState enumeration Value Description

Added The row has been added to the collection of rows in the table but

AcceptChanges( ) has not been called

Deleted The row has been deleted from the collection of rows in the table but

AcceptChanges( ) has not been called

Detached The row does not belong to the collection of rows in a DataTable

Modified The data in the row has been changed but AcceptChanges( ) has not been

called

Unchanged The data in the row has not been changed since it was loaded or since

AcceptChanges( ) was last called

When AcceptChanges( ) is called on the DataSet, DataTable, or DataRow, either

explicitly or implicitly by calling the Update( ) method of the DataAdapter, the following occurs:

• All rows with a row state of Deleted are removed

• All other rows are assigned a row state of Unchanged and the Original row version

values are overwritten with the Current version values

When RejectChanges( ) is called on the DataSet, DataTable, or DataRow, the following occurs:

• All rows with a row state of Added are removed

• All other rows are assigned a row state of Unchanged and the Current row version

values are overwritten with the Original row version values

Each DataRow has a RowState property that returns the current state of the row

ADO.NET maintains several versions of the data in each row while it is being modified

to allow the disconnected to be later reconciled with the data source Table 2-5 describes

the DataRowVersion enumeration values

Table 2-5 DataRowVersion enumeration Value Description

Current Current value This version does not exist for rows with a state of Deleted

Default

Default value as determined by the DataRowState:

• The Current version for rows with Added, Modified, or Unchanged state

• The Original version for rows with Deleted state

• The Proposed value for rows with Detached state

Original Original value This version does not exist for rows with a state of Added

Proposed Proposed value This value exists during a row edit operation started either

implicitly or explicitly with the BeginEdit( ) method and for Detached rows

The HasVersion( ) method of the DataRow object checks whether a particular row

version exists

The DataViewRowState enumeration is used to retrieve a particular version of data or to

determine whether a version exists It is used for this purpose by both the Select( )

method of the DataTable and by the RowStateFilter property of the DataView You can

retrieve more than one version by using a Boolean OR of DataViewRowState values

Table 2-6 describes the DataViewRowState enumeration values

Table 2-6 DataViewRowState enumeration Value Description

Added The Current version of all Added rows

CurrentRows The Current version of all Unchanged, Added, and Modified rows

This is the default value

Deleted The Original version of all Deleted rows

ModifiedCurrent The Current version of all Modified rows

ModifiedOriginal The Original version of all Modified rows

None No rows

OriginalRows The Original version of Unchanged, Modified, and Deleted rows Unchanged The Current version of all Unchanged rows

The Current version of each row is retrieved by default when accessing rows in a

DataTable or in a DataView The solution demonstrates an approach for getting Deleted rows from both a DataTable and a DataView Deleted rows include only those marked for deletion using the Delete( ) method of the DataRow or the DataView, not the

Remove( ) or RemoveAt( ) method of the DataRowCollection, which instead

immediately removes the specified DataRow from the collection

The solution demonstrates two techniques for retrieving the deleted rows:

To get the Deleted rows from the DataTable, use an overload of the Select( ) method of the DataTable to return an array of deleted DataRow objects The overload accepts an argument having a DataViewRowState enumeration value To retrieve deleted rows, pass

a value of Deleted as the argument

To get the Deleted rows from the DataView, set the RowStateFilter property of the DataView to Deleted Deleted rows are also visible, along with other rows, when you set the RowStateFilter property to ModifiedOriginal and OriginalRows

[ Team LiB ]