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� Exercise 1: Working with DataTable Objects This practice will provide code examples that demonstrate adding data to a table, deleting rows in a table, and editing existing values in

The RowState is used to determine the state of a row When first populated, the rows

in a DataTable have a RowState of Unchanged Table 7-3 details the different values of the RowState enumeration

Table 7-3 RowState Enumeration

Value Description

Unchanged No changes have been made since the last AcceptChanges call or

since the initial filling of the DataTable

Added This row has been added since the last AcceptChanges call

Modified This row has been updated since the last AcceptChanges call

Deleted This row has been deleted from the DataTable since the last

AcceptChanges call

Detached This row has not yet been added to any DataTable.Rows collection

In addition to RowState, each row also maintains different versions after changes are made These differing versions are accessed by passing a value from the DataRow-

Version enumeration as an argument in addition to the column index when accessing

the data in a row For example, you can access the current and original values of a col­

umn in a specific DataRow to perform processing prior to calling AcceptChanges

Accepting and Rejecting Changes to a DataTable

When all changes to a row are deemed valid, you can accept the modifications by call­

ing the DataRow.AcceptChanges method Calling the AcceptChanges method sets the

RowState of the row to Unchanged and commits all current values to original You can

call AcceptChanges on the DataRow, DataTable, or entire DataSet If you decide to abort changes instead of accepting them, call the RejectChanges method of the DataRow,

DataTable, or DataSet

DataTable Events

DataTable objects expose several events that are raised when changes are being made

to the data in the table

The main events available when working with DataTable objects are listed in Table 7-4

Table 7-4 DataTable Events

Event Desription

ColumnChanged Raised after a value is inserted into a column

ColumnChanging Raised when a value is submitted to change a column

RowChanged Raised after a row in the table has been edited

RowChanging Raised when a row in the table is edited

RowDeleted Raised after a row is marked for deletion

RowDeleting Raised when a row is marked for deletion

Row Errors

When errors are encountered during the processing of DataRows, a value is added to the RowError property The RowError property is a string that is typically set to an error

message describing the error, but it can be set to any string and used as needed in your

application Once a DataRow.RowError property is assigned, the DataTable.HasErrors property is automatically set to True, indicating errors exist in the DataTable When it

is determined that errors exist, you can use the DataTable.GetErrors method to return

an array of DataRows containing all rows that have errors or, more specifically, all rows with a RowError value other than null (nothing, or the empty string)

To remove an error, set the DataRow.RowError property to an empty string

Quick Check

1 How do you add data to a DataTable?

2 How do you commit pending modifications to the data in a DataTable?

Quick Check Answers

1 Create a new DataRow and add it to the DataTable.Rows collection

2 By calling AcceptChanges on the DataRow, DataTable, or DataSet

Lab: Working with Data in a DataTable

In this lab you will manipulate the data in a DataTable

� Exercise 1: Working with DataTable Objects

This practice will provide code examples that demonstrate adding data to a table, deleting rows in a table, and editing existing values in a data row and how to view the

RowState and DataRowVersion information for records in a DataTable After modifying

records, the AcceptChanges and RejectChanges methods will be demonstrated as well

1 Create a Windows application and name it WorkingWithDataTables

2 Add a DataGridView to the form and change its Name property to

Customers-DataGridView

3 Add a button to the form and set the following properties:

❑ Name = FillTableButton

❑ Text = Fill Table

4 Drop a SqlDataAdapter from the Toolbox onto the form to start the Data Adapter

Configuration Wizard

NOTE SqlDataAdapter Toolbox item

If the SqlDataAdapter is not in the Toolbox, right-click the Data section of the Toolbox, select Choose Items, and then select the SqlDataAdapter item on the NET Framework Components

tab Click OK

5 Select or create a new connection to the Northwind database and click Next

6 Leave the default option to Use SQL Statements, and then click Next

7 Type SELECT * FROM Customers on the Generate The SQL Statements page

8 Right-click SqlDataAdapter1 in the component tray and select Generate DataSet

9 In the Generate DataSet dialog box, replace DataSet1 with NorthwindDataSet

Figure 7-11 Form1 in the VS IDE after configuring the DataAdapter and generating the

DataSet

10 Add the System.Data.SqlClient namespace to your form

11 Create a Form Load event handler and add the following code to the Form1_Load

❑ Name = AddRowButton

❑ Text = Add Row

13 Create a button-click event handler for the AddRowButton and add the following

code:

' VB

' Create a new instance of a Customers row

Dim NewRow As NorthwindDataset.CustomersRow = _

MessageBox.Show(ex.Message, "Add Row Failed");}

14 Add the following code to the form class that creates a function to return the

CustomersRow selected in the grid:

' VB

CustomersDataGridView.CurrentRow.Cells("CustomerID").Value.ToString ' Using the SelectedCustomerID get the selected row

Dim SelectedRow As NorthwindDataset.CustomersRow = _ NorthwindDataset1.Customers.FindByCustomerID(SelectedCustomerID)

15 Add a button to the form and set the following properties:

❑ Name = DeleteRowButton

❑ Text = Delete Row

16 Create a button-click event handler for the DeleteRowButton and add the follow­

17 Add three buttons to the form and set the following properties:

❑ Text = Reject Changes

18 Add a TextBox next to the UpdateValueButton and set its Name property to

The Form layout should appear similar to Figure 7-12

Figure 7-12 The Form layout

20 Add the following code to the form class that updates the text boxes with the

row versions and row state:

' VB

CurrentDRVTextBox.Text = GetSelectedRow.Item _

(CustomersDataGridView.CurrentCell.OwningColumn.Name, _ DataRowVersion.Current).ToString

Catch ex As Exception CurrentDRVTextBox.Text = ex.Message End Try

Try OriginalDRVTextBox.Text = GetSelectedRow.Item _ (CustomersDataGridView.CurrentCell.OwningColumn.Name, _ DataRowVersion.Original).ToString

Catch ex As Exception OriginalDRVTextBox.Text = ex.Message End Try

' Display the current RowState of the selected row RowStateTextBox.Text = GetSelectedRow.RowState.ToString End Sub

} catch (Exception ex) {

CurrentDRVTextBox.Text = ex.Message;

} try { OriginalDRVTextBox.Text = GetSelectedRow() [CustomersDataGridView.CurrentCell.OwningColumn.Name, DataRowVersion.Original].ToString();

} catch (Exception ex) {

OriginalDRVTextBox.Text = ex.Message;

} // Display the current RowState of the selected row RowStateTextBox.Text = GetSelectedRow().RowState.ToString();

}

21 Create an event handler for the UpdateValueButton_Click event and add the fol­

lowing code:

' VB

// C#

22 Create an event handler for the CustomersDataGridView_CellClick event and add

the following code:

26 Click around the grid and notice that the Original and Current values show as the

same, and the RowState display is Unchanged

27 Now click the cell that contains Maria Anders (in the first row) and type Maria AndersEdited in the CellValueTextBox

28 Click the UpdateValue button and notice that the value is updated in the grid,

the Current and Original text boxes display the different versions of the record,

and the RowState has been changed to read Modified

29 Now click the Add Row button

30 Scroll down to the bottom of the grid and select one of the cells in the new

Figure 7-13 Form after clicking the Add Row button

31 Scroll back to the row with the MariaAndersEdited field and select it

32 Click the RejectChanges button and inspect the row version and row state values

33 Scroll to the WINGT record and select it

34 Click the Accept Changes button and inspect the row version and row state values

■ Delete rows in a DataTable by calling the Delete method of a DataRow

■ Monitor and keep track of changes to DataRow objects by using the RowState and RowVersion enumerations

■ DataTable events are raised as data is changed in specific DataColumn objects or

entire DataRow objects

■ Set the RowError property of a DataRow to indicate a row with an error

Lesson Review

The following questions are intended to reinforce key information presented in this lesson The questions are also available on the companion CD if you prefer to review them in electronic form

NOTE Answers

Answers to these questions and explanations of why each choice is correct or incorrect are located

in the “Answers” section at the end of the book

1 When adding a new row to a DataTable:

A Create an instance of a DataRow and call the Update method of the

Data-Adapter

B Create an instance of a DataRow (or typed row), and add it to the Rows col­

lection of the DataTable

C Call the DataTable.NewRow method

D Create an instance of a DataRow

2 How do you access the original value in the CustomerId column?

A OriginalValue = DataRow(“CustomerID”).DataRowVersion.Original

B OriginalValue = DataColumn(“CustomerID”).Original

C OriginalValue = DataRow(“CustomerID”, DataRowVersion.Original)

D OriginalValue = DataRow(“CustomerID”)

3 What DataTable event would you handle to validate for an acceptable value in a

column? (Choose all that apply.)

A ColumnChanged

B ColumnChanging

C RowChanged

D RowChanging

Lesson 5: Working with XML in DataSet Objects

This lesson describes how to use DataSet objects when working with data formatted

as XML DataSet objects can be filled from an XML document or an XML stream, and they can load or write out their schema information DataSet objects have several

methods for working with XML data that will be described in the following examples

After this lesson, you will be able to:

■ Represent data in a DataSet using XML

❑ Load a DataSet from an XML stream or document

❑ Write a DataSet as XML data

❑ Load DataSet schema information from an XML stream or document

❑ Write DataSet schema information as XML schema (XSD)

❑ Synchronize a DataSet with an XmlDataDocument

❑ Perform an XPath query on a DataSet

❑ Apply an XSLT transform to a DataSet

❑ Create nested DataRelation objects in a DataSet to represent XML data

❑ Generate DataSet relational structures from XML schema (XSD)

❑ Map XML schema (XSD) constraints to DataSet constraints

❑ Infer DataSet structures from an XML stream or document

Estimated lesson time: 60 minutes

Writing a DataSet as XML Data

To save the data in a DataSet as XML-formatted data, use the WriteXml method of the

DataSet You can save the XML data directly to a file, or you can write it to a stream

Call the WriteXml method of a DataSet to save the contents of all tables in the DataSet

as XML or call the WriteXml method of an individual DataTable to write the data from

only that table

The following code example saves the data in the NorthwindDataSet to a file named

Northwind.xml

' VB

NorthwindDataset.WriteXml("Northwind.xml")

// C#

NorthwindDataset.WriteXml("Northwind.xml");

Writing DataSet Schema Information as XML Schema

To save a DataSet object’s schema information, use the WriteXmlSchema method of the DataSet You can save the XML schema information directly to a file, or you can write it to a stream Call the WriteXmSchema method of a DataSet to save the schema

of the entire DataSet or call the WriteXmlSchema method of an individual DataTable to

write the schema from only that table

The following code example saves the data in the NorthwindDataSet object’s schema

information to a file named Northwind.xsd

' VB

NorthwindDataset.WriteXmlSchema("Northwind.xsd")

// C#

NorthwindDataset.WriteXmlSchema("Northwind.xsd");

Loading a DataSet from an XML Stream or Document

To load XML data into a DataSet, use the ReadXml method of the DataSet You can

read the XML data directly from a file, or you can read it from a stream Call the

ReadXml method of a DataSet to load the entire DataSet or call the ReadXml method

of an individual DataTable to load only the data for that table

The following code example loads the NorthwindDataSet from the contents of a file

To load schema information into a DataSet, use the ReadXmlSchema method of the

DataSet Load the XML schema information directly from an xsd file or read it from

a stream Call the ReadXmlSchema method of a DataSet to load the entire DataSet or

call the ReadXmlSchema method of an individual DataTable to load the schema for

only that table

The following code example reads the schema information into the NorthwindDataSet

from a file named Northwind.xsd

' VB

NorthwindDataset.ReadXmlSchema("Northwind.xsd")

// C#

NorthwindDataset.ReadXmlSchema("Northwind.xsd");

Synchronizing a DataSet with an XmlDataDocument

When working with XML data and DataSet objects, you will typically need to manip­ ulate data through the DataSet classes as well as XML classes available in the NET Framework Keeping your DataSet and XmlDataDocument in synch allows you to pro­

cess the data using whichever method of access you prefer while working on the same data source

The following code example shows how to create a new XmlDataDocument and syn­ chronize it with the NorthwindDataSet

' VB

Dim NwDataDocument As New XmlDataDocument(NorthwindDataset)

// C#

XmlDataDocument NwDataDocument = new XmlDataDocument(NorthwindDataset);

Perfoming an XPath Query on a DataSet

You can perform XPath queries against data in a DataSet after synchronizing a DataSet with an XmlDataDocument Pass an XPath query to the XmlDataDocument.Document-

Element.SelectNodes method The SelectNodes method returns the data as a collection

of Xml.XmlNode objects

The following code example shows how to execute an XPath query and iterate through the results:

' VB

row = NwDataDocument.GetRowFromElement(CType(xmlNode, Xml.XmlElement))

If row IsNot Nothing Then

// C#

DataRow row;

Xml.XmlDataDocument NwDataDocument = new Xml.XmlDataDocument(NorthwindDataset)

Xml.XmlNodeList CustomerNodes = NwDataDocument.DocumentElement.SelectNodes("*");

foreach (Xml.XmlNode xmlNode In CustomerNodes)

{

Lab: Working with XML in DataSets

In this lab you will load and save XML Data to a Dataset

� Exercise 1: Saving a DataSet Objects as XML

This example takes the data from a DataSet and saves it as formatted XML in a file

named Northwind.xml

1 Create a Windows application and name it SavingDataSetsAsXml

2 Drag a SqlDataAdapter onto the form to start the Data Adapter Configuration

Wizard

3 Select a connection to the Northwind sample database

4 On the Choose A Command Type page, select the default value of Use SQL

Statements Then, click Next

5 On the Generate The SQL Statements page, type SELECT * FROM Customers

Then, click Finish

6 Change the name from SqlDataAdapter1 to CustomersAdapter

7 Drag a second SqlDataAdapter onto the form to start the Data Adapter Configu­

ration Wizard again

8 On the Choose A Command Type page, select the default value of Use SQL

Statements Then, click Next

9 Type SELECT * FROM Orders in the Generate the SQL statements page Then,

click Finish

10 Change the name from SqlDataAdapter1 to OrdersAdapter

11 Right-click the CustomersAdapter in the component tray and select Generate

DataSet

12 Name the new DataSet NorthwindDataSet (replacing DataSet1) Select both the

Customers and Orders tables and click OK

13 Drag a DataGridView onto the form and set its Name property to CustomersGrid

14 Drag a button onto the form and set the following properties:

❑ Name = FillDataSetButton

❑ Text = Fill DataSet

15 Drag a second button onto the form and set the following properties:

❑ Name = SaveXmlDataButton

❑ Text = Save XML Data

16 Drag a third button onto the form and set the following properties:

❑ Name = SaveXmlSchemaButton

❑ Text = Save XML Schema

17 Double-click the Fill DataSet button to create the button-click event handler

18 Add the following code to the FillDataSetButton_Click event handler:

' VB

// C#

19 Double-click the Save Xml Data button to create the button-click event handler

20 Add the following code to the SaveXmlDataButton_Click event handler:

' VB

// C#

try

{

northwindDataSet1.WriteXml(@"C:\DataSources\Northwind.xml");

MessageBox.Show("Data saved as Northwind.xml");

21 Double-click the Save Xml Schema button to create the button-click event han­

// C#

try

{

NorthwindDataset1.WriteXmlSchema(@"C:\DataSources\Northwind.xsd");

MessageBox.Show("Schema saved as Northwind.xsd");

23 Run the application and click the Fill DataSet button

The NorthwindDataSet is filled with data and the Customers table is displayed in

the grid

24 Click the Save Xml Data button

The Northwind.xml file is saved to the C:\Datasources directory

25 Click the Save Xml Schema button

The Northwind.xsd file is saved to the C:\Datasources directory

26 Navigate to the C:\Datasources directory and open the Northwind.xml and

Northwind.xsd files to verify that the data and schema information was saved to the files

The Northwind.xml and Northwind.xsd files are required for the next practice

� Exercise 2: Loading DataSet Objects with XML Data

This example creates an untyped DataSet and defines its schema based on the con­

tents of the Northwind.xsd file After loading the schema information, you will load

the DataSet with the contents of the Northwind.xml file and display it in a grid This

practice expects the Northwind.xml and Northwind.xsd files to be available in the C:\Datasources directory

1 Create a Windows application and name it LoadDataSetsWithXml

2 Add a DataGridView to the Form and name it CustomersGrid

3 Add another DataGridView to the form and name it OrdersGrid

4 Drag a button onto the form and set the following properties:

❑ Name = LoadSchemaButton

❑ Text = Load Schema

5 Drag a button onto the form and set the following properties:

❑ Name = LoadDataButton

❑ Text = Load Data

6 Create an event handler for the LoadSchemaButton_Click event (double-click the

Load Schema button) and add the following code:

' VB

// C#

7 Create an event handler for the LoadDataButton_Click event (double-click the

Load Data button) and add the following code:

8 Run the application and click the Load Schema button

The grids display the columns for the Customers and Orders tables based on the schema information loaded from the Northwind.xsd file

9 Click the Load Data button

The contents of the Northwind.xml file are loaded into the DataSet and dis­

played in their respective grids on the form

Lesson Summary

■ The data in a DataSet can be written out as XML data

■ The schema of a DataSet can be written out as XML Schema (an xsd file)

■ The data in an XML file or document can be loaded into a DataSet

■ The schema information in an xsd file can be loaded into a DataSet

■ A DataSet and an XMLDataDocument can be kept in synch so you can manipu­

late the data and have it be reflected in both objects

■ XPath queries can be performed on DataSet data

Lesson Review

The following questions are intended to reinforce key information presented in this lesson The questions are also available on the companion CD if you prefer to review them in electronic form

NOTE Answers

Answers to these questions and explanations of why each choice is correct or incorrect are located

in the “Answers” section at the end of the book

1 How do you load the schema information from an xsd file into a DataSet?

A Call the GetXmlSchema method passing in the path to the xsd file to the

method

B Call the ReadXml method passing in the path to the xsd file to the method

C Call the ReadXmlSchema method passing in the path to the xsd file to the

method

D Set the DataSet’s Name property to the xsd filename

2 How do you synchronize a DataSet with an XmlDataDocument?

A By passing the XmlDataDocument to the DataSet.GetXml method

B By declaring a new instance of an XmlDataDocument and passing in the

name of the DataSet you want to synchronize with

C By calling the XmlDataDocument.Load method

D By calling the XmlDataDocument.Synch method

3 How do you execute an XPath query on a DataSet?

A Synchronize with an XML document and perform the XPath query on the

raw XML

B Pass the XPath query as a string to the DataTable.Select method

C Pass the XPath query as a string to the DocumentElement.SelectNodes

method of a synchronized XmlDataDocument

D Pass the XPath query as a string to the DataTable.Find method

Lesson 6: Creating and Using DataView Objects

This lesson describes how to work with DataView objects (System.Data.DataView)

DataView objects provide a way to work with DataTable objects and can be dis­

played in data-bindable controls such as a DataGridView DataView objects provide

sorting and filtering capabilities as well as the ability to modify the data in the

related DataTable

After this lesson, you will be able to:

■ Create and use DataView objects

❑ Create a DataView

❑ Sort and filter data using a DataView

❑ View data using a DataView

❑ Search for data within a DataView

❑ Navigate relationships using a DataView

❑ Modify data using a DataView

❑ Handle DataView events

❑ Set default table views using a DataViewManager

Estimated lesson time: 45 minutes

Creating DataView Objects

You can create new DataView objects or reference an existing DataView Create new

DataView objects by generating a new instance of a DataView and passing in the

name of the DataTable for the view to represent or display DataTable objects actually have a DefaultView property that contains the DataView the table uses by default Reference this existing DataView by assigning an instance of a DataView to the

DataTable.DefaultView property DataView objects offer the advantage of allowing

you to bind multiple controls to the same data source and to display different records or different sort orders

The following code samples show how to create DataView objects as previously

described

' VB

// C#

Sorting and Filtering Data Using a DataView

Sort data in a DataView by setting the DataView.Sort property to the column name you

want to sort on To sort on multiple columns, separate column names with a comma (,) Complete the Sort expression with ASC to sort in ascending order, or DESC to sort

in descending order (ASC is the default behavior.)

The following code sample sorts the DataView in descending order on the

Contact-Name column:

' VB

CustomersDataView.Sort = "ContactName DESC"

// C#

CustomersDataView.Sort = "ContactName DESC";

Viewing Data Using a DataView

In most cases, you will probably bind DataView objects to controls such as the

Data-GridView or, maybe, data bind each column in a DataRowView to individual controls

such as TextBox objects For situations in which you need to programmatically access the data in a DataView, it is important to note that a DataView contains a collection of

DataRowView objects that represent the rows in the related DataTable Each View contains an array representing the columns in the row To access the individual

DataRow-values in each column, iterate over the DataRowView objects and read the column

through the index or column name

The following code example assigns the values of the first and second columns to the

RowValues variable:

' VB

' Access column values by passing the column name to access the DataRowView column

' Access column values by passing the column index to access the DataRowView column

Dim FullName As String = DataRowView(0).ToString() & " " & DataRowView(1).ToString()

// C#

// Access column values by passing the column name to access the DataRowView column

string FullName = DataRowView("FirstName").ToString() + " " +

DataRowView("LastName").ToString();

// Access column values by passing the column index to access the DataRowView column

string FullName = DataRowView(0).ToString() + “ ” + DataRowView(1).ToString();

Modifying the Data in a DataView

You can edit values in a row by accessing the individual column values in a

DataRow-View and assigning the new value to the column (item array of the DataRowDataRow-View)

The following code sample assigns a value of Steve to the FirstName column of the selected DataRowView:

' VB

// C#

Searching Data in a DataView

Search for records in a DataView using the Find and FindRows methods Pass a value

to the Find or FindRows method and both methods search for that value in the column set in the Sort property In other words, if the DataView.Sort is set to CustomerID, pass

CustomerID values to the Find and FindRows methods; if the DataView.Sort property is

set to ContactName, pass ContactName to the Find and FindRows methods

The following code example sets the sort key to the CustomerID column, and then it

calls the Find method and passes in ALFKI (the CustomerID) as the search string

' VB

// C#

Navigating Related Data in a DataView

You can retrieve records from related tables using DataViews as long as the DataTable associated with the DataView is related to another DataTable through a DataRelation object To display the related records, call the CreateChildView method of a DataRow-

View and pass in the name of the DataRelation that relates the DataTable objects This

creates a new DataView containing only the related records

The following code creates a DataView made up of orders for a selected customer

Working with DataView Events

The main event to program against for a DataView is the ListChanged event The

ListChanged event is raised when data or schema changes occur in the underlying DataTable, or if changes are made to a DataRelation attached to the DataView object’s