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ADO.NET provides several objects, such as DataSet and DataTable objects, for caching data in applications so that you can disconnect from the database and work with the data in your ap

1 How do you create a new transaction?

A Assign a transaction variable the return value of the

Connection.Begin-Transaction method

B Declare a new instance of the Transaction class

C Call the Command.CreateTransaction method

D Declare a new Command.Transaction object

2 What is the main purpose of a transaction?

A To validate that multiple commands complete successfully

B To handle exceptions that may occur on the database during command

execution

C To abort the outcome of an executed command and return data to the state

it was in prior to the transaction

D To provide an option to abort the outcome of executed commands and

return data to the state it was in prior to the transaction

3 What is the difference between a local transaction and a distributed transaction?

A Local transactions are performed on a single database table, whereas dis­

tributed transactions are performed on multiple database tables

B Local transactions are performed on a single database, whereas distributed

transactions are performed on multiple databases on the same server

C Local transactions are performed on a single database server, whereas dis­

tributed transactions can be performed across multiple database servers

D Local transactions are performed on a database on the local machine,

whereas distributed transactions are performed on a database on a remote machine

Chapter Review

To further practice and reinforce the skills you learned in this chapter, you can per­form the following tasks:

■ Review the chapter summary

■ Complete the case scenarios These scenarios set up real-world situations involv­ing the topics of this chapter and ask you to create a solution

■ Complete the additional practices

■ Take a practice test

■ Command objects have parameter collections that can contain one or more

parameters for executing parameterized queries and stored procedures

■ BLOB data can be saved and retrieved from a database using DataReaders and

Stream objects

■ Bulk copy operations can be performed using the SqlBulkCopy object as well as

by executing a SQL BULK INSERT statement

■ Commands can be executed within the context of a local transaction, or a com­mand can be enlisted in a distributed transaction

Key Terms

■ BLOB

■ parameter

■ transaction

Case Scenarios

In the following case scenarios, you will apply what you’ve learned about working with data in a connected environment You can find answers to these questions in the

“Answers” section at the end of this book

Case Scenario 1: Troubleshooting a Non-Performing Application

You’ve been contracted by The Phone Company to investigate why their Customer Relationship Management (CRM) application is running slow, causing support techs

to spend an unreasonable amount of time waiting for queries to execute After several days of analyzing their code base and backend database, you come to the conclusion that the lack of performance is due to the exponential increase of their customer base, which is causing too many records to be fetched when running queries that were not designed with scalability in mind You also notice the archiving utility is constantly running, moving individual records from current to history

List the potential improvements you can make to the application

Case Scenario 2: Preventing the Inventory System from Selling

Unavailable Products

Your biggest customer, Wide World Importers, is now selling items from many new manufacturers around the globe Their system is set up to forward orders to the cor­rect manufacturers if local warehouses are out of stock so items can be drop-shipped

to the proper customers The main problem this poses is that they seem to be forward­ing orders for items that are not in stock or have longer than acceptable lead times, and it’s causing customers to become extremely upset

Given that each manufacturer exposes its inventory information and projected man­ufacture date for new inventory, what modifications can you make to the Wide World Importers sales application to remedy this problem?

■ Practice 2 Create an application that queries the Northwind Customers table

and has separate commands to return data based on CompanyName, City, or

PostalCode

■ Practice 3 Create an application that bulk copies all Northwind Orders, which have already shipped, into a ShippedOrders table

Take a Practice Test

The practice tests on this book’s companion CD offer many options For example, you can test yourself on just the content covered in this chapter, or you can test yourself on all the 70-526 certification exam content You can set up the test so that it closely sim­ulates the experience of taking a certification exam, or you can set it up in study mode

so that you can look at the correct answers and explanations after you answer each question

MORE INFO Practice tests

For details about all the practice test options available, see the “How to Use the Practice Tests” sec­ tion in this book’s Introduction

Create, Add, Delete, and Edit Data

in a Disconnected Environment

This chapter describes how to work with data loaded from a database or XML docu­

ment into your application ADO.NET provides several objects, such as DataSet and

DataTable objects, for caching data in applications so that you can disconnect from

the database and work with the data in your application and then reconnect when you are ready to save your updates back to the data source

Exam objectives in this chapter:

■ Create, add, delete, and edit data in a disconnected environment

❑ Create a DataSet graphically

❑ Create a DataSet programmatically

❑ Add a DataTable to a DataSet

❑ Add a relationship between tables within a DataSet

❑ Navigate a relationship between tables

❑ Merge DataSet contents

❑ Copy DataSet contents

❑ Create a typed DataSet

❑ Create DataTables

❑ Manage data within a DataTable

❑ Create and use DataViews

❑ Represent data in a DataSet by using XML

❑ Use the OleDbDataAdapter object to access an ADO Recordset or Record

❑ Generate DataAdapter commands automatically by using the

Command-Builder object

329

❑ Generate DataAdapter commands programmatically

❑ Populate a DataSet by using a DataAdapter

❑ Update a database by using a DataAdapter

❑ Resolve conflicts between a DataSet and a database by using a DataAdapter

❑ Respond to changes made to data at the data source by using DataAdapter

events

❑ Perform batch operations by using DataAdapters

Lessons in this chapter:

■ Lesson 1: Creating DataSet Objects 332

■ Lesson 2: Creating DataTable Objects 349

■ Lesson 3: Creating DataAdapter Objects 358

■ Lesson 4: Working with Data in DataTable Objects 373

■ Lesson 5: Working with XML in DataSet Objects 387

■ Lesson 6: Creating and Using DataView Objects 396

Before You Begin

To complete the lessons in this chapter, you must have:

■ A computer that meets or exceeds the minimum hardware requirements listed in the “Introduction” at the beginning of the book

■ Microsoft Visual Studio 2005 Professional Edition installed on your computer

■ An understanding of Microsoft Visual Basic or C# syntax and familiarity with the Microsoft NET Framework

■ Available data sources, including Microsoft SQL Server (SQL Server Express Edi­ tion is acceptable), the Northwind sample database for SQL Server, and the Nwind.mdb Microsoft Office Access database file

■ A basic understanding of relational databases

■ Completed the exercises or understood the concepts presented in Chapter 5,

“Configuring Connections and Connecting to Data,” and Chapter 6, “Working with Data in a Connected Environment.”

Real World

Steve Stein

I always spent way too much time whenever I needed to create objects to cache

data in my applications With DataSet objects, the standard database structures

are already there, so quickly creating a representative object model for my data

is really easy

Lesson 1: Creating DataSet Objects

DataSet objects are available in the System.Data namespace and are used as an

in-memory cache of the data being used in your application DataSet objects contain

DataTable objects that can be related with DataRelation objects much like the struc­

ture of a relational database

After this lesson, you will be able to:

■ Create a DataSet graphically

■ Create a typed DataSet

■ Create a DataSet programmatically

■ Add a DataTable to a DataSet

■ Add a relationship between tables within a DataSet

■ Navigate a relationship between tables

Estimated lesson time: 45 minutes

DataSet Objects

Datasets are objects that you use to temporarily store the data that is used in your

application There are basically two distinct kinds of DataSet objects: typed, and untyped Untyped DataSets are the standard generic instances of the DataSet class where you manually build up the DataSet definition (schema) by creating DataTable objects (untyped DataTables) and adding them to the Tables collection in the DataSet You can access untyped DataTable and DataColumn objects through their collection indices Typed DataSet objects derive their schema from an xsd file and contain explicitly typed collections (such as a specific CustomersTable object)

There are three distinct ways to create DataSet objects in Visual Studio:

■ Declare a new DataSet object programmatically in the code editor, which results

in an empty DataSet that requires creating DataTable and optional DataRelation objects to be added to the DataSet

■ Use design-time tools such as the DataSet Designer and the Data Source Con­

figuration Wizard which assists in the creation of typed DataSet objects by step­

ping you through the process of selecting or creating a data connection and then allowing you to select database objects available from that connection to

build up a typed DataSet and have most, if not all, of the necessary code gener­

ated for you

■ Drag a DataSet object from the Toolbox onto a form and use the Table and Col­ umn Collection editors to build up the schema of your DataSet

This lesson describes how to create DataSet objects using each of these methods

NOTE Generating DataSet objects

You can also create DataSet objects based on configured DataAdapter objects This will be covered

in Lesson 3, “Creating DataAdapter Objects,” of this chapter

Creating DataSet Objects Programmatically

Create DataSet objects by declaring instances of them You can optionally provide the name of the DataSet For example, the following code example creates a new DataSet named NorthwindDataSet:

' VB

Dim NorthwindDataset As New DataSet ("NorthwindDataset")

// C#

DataSet NorthwindDataset = new DataSet ("NorthwindDataset");

Adding DataTable Objects to a DataSet

After declaring a new DataSet, you need to add DataTable objects to it to actually hold the data in your application The following code sample shows how to add a Customers-

Table and OrdersDataTable to the NorthwindDataset:

' VB

// C#

Adding a Relationship Between Tables in a DataSet

After adding tables to a DataSet, you can use DataRelation objects to represent the rela­ tion between DataTable objects just like the relationships between tables in a data­ base Create relationships in DataSet objects by declaring DataRelation objects and providing the columns from the parent and child tables to the DataRelation construc­ tor After creating the relationship, you must add it to the Relations collection of the

' Create the new relationship

Dim CustomersOrders As New DataRelation ("CustomersOrders", _

CustomersTable.Columns("CustomerID"), OrdersTable.Columns("CustomerID"))

// C#

// Create the new relationship

DataRelation CustomersOrders = new DataRelation ("CustomersOrders",

CustomersTable.Columns["CustomerID"], OrdersTable.Columns["CustomerID"]);

Navigate a Relationship Between Tables

To access related records in DataTable objects, you must first select a DataRow from either the parent or child table and then call either the GetParentRow or GetChildRows method of the DataRow Calling the GetParentRow method returns a single DataRow representing the parent record, whereas calling the GetChildRows method returns an array of DataRows representing all rows that are related to the selected parent

Returning the Parent Row of a Selected Child Record The following example returns

the Customer of a selected Order:

Returning the Related Child Rows of a Selected Parent Row The following example

returns the Orders of a selected Customer:

' VB

Dim Orders() As DataRow = SelectedCustomersRow.GetChildRows("FK_Orders_Customers")

// C#

DataRow Orders() = SelectedCustomersRow.GetChildRows("FK_Orders_Customers");

Merging DataSet Contents

You can take the contents from one DataSet (the source dataset) and merge it with the contents of another DataSet (the target dataset) using the DataSet.Merge method

When merging datasets, the actual data is combined depending on whether a similar

record exists in the DataSet into which it will be merged For example, if you merge

two datasets that both contain a record with the same primary key, the values in the

target DataSet will be overwritten with the new values in the source DataSet You can control this behavior and restrict changes from being made in the target DataSet by passing in a true or false value to the PreserveChanges flag in the Merge method In addition to merging the actual data, when you merge two DataSets that have tables

with differing schema, you can pass an optional MissingSchemaAction parameter to

the Merge method that controls the behavior of the merge when the source DataSet has objects that are not currently in the target DataSet The following are valid values

for the MissingSchemaAction parameter:

■ Add (default) All schema items in the source DataSet are added to the target

DataSet and populated

■ AddWithKey All schema items and primary key settings are added to the target

DataSet

■ Error An exception will be thrown when the schemas in the source and target

DataSets do not match

■ Ignore All schema inconsistencies between the source and target DataSets are

ignored

In the following code example, the contents of the OldSalesDataSet are merged into

the contents of the SalesHistoryDataSet The PreserveChanges parameter is set to True

and any schema differences will be ignored

' VB

SalesHistoryDataSet.Merge(OldSalesDataSet, True, MissingSchemaAction.Ignore)

// C#

SalesHistoryDataSet.Merge(OldSalesDataSet, true, MissingSchemaAction.Ignore);

Copying DataSet Contents

In some situations you may need to create a copy of the data in a DataSet For exam­

ple, you might need to manipulate a copy of the data and perform some processing,

but you might not want to modify the original data To create a copy of a DataSet, you simply create a new DataSet object and assign it the return value of the DataSet Copy

method The following code example demonstrates this:

' VB

// C#

Lab: Creating DataSet Objects

In this lab you will create typed and untyped DataSet objects

� Exercise 1: Creating a DataSet with the DataSet Designer

The DataSet Designer is a design-time tool that assists in the creation of typed DataSet

objects by allowing you to drag and drop database tables from Server Explorer onto

the design surface As you drop tables on the surface, they are added to the DataSet as

typed objects that make programming as simple as writing the table and column names you want to access

1 Create a Windows application and name it DataSetDesignerExample

2 From the Project menu, select Add New Item

3 Select the DataSet template and name it NorthwindDataSet.xsd

4 Navigate to the Customers table in Server Explorer and drag it onto the design

surface

5 Navigate to the Orders table in Server Explorer and drag it onto the design sur­

face

After dropping the Customers and Orders tables onto the DataSet Designer, the

design surface should look similar to Figure 7-1

Figure 7-1 Customers and Orders DataTable objects and TableAdapter objects as seen in the

DataSet Designer

6 Build the project before moving on to the next step

7 Drag a ListBox onto Form1 and name it CustomersListBox

8 Drag a button onto Form1 and set the following properties:

❑ Name = GetCustomersButton

❑ Text = Get Customers

9 Double-click the Get Customers button and add the following code to the

GetCustomersButton_Click event handler:

' VB

10 Run the application and click the Get Customers button Verify that the

Company-Name from each customer is displayed in the CustomersListBox similar to Figure 7-2

Figure 7-2 The CompanyName from all customers appearing in the CustomersListBox after

clicking the Get Customers button

� Exercise 2: Creating a Typed DataSet with the Data Source Configuration Wizard

This exercise provides instructions for creating a strongly typed DataSet using the

Data Source Configuration Wizard

1 Create a Windows application and name it DataSourceWizardExample

2 Start the Data Source Configuration Wizard by selecting Add New Data Source

from the Data menu

NOTE Data menu

If the Data menu is not available, open the form in Design view

3 Leave the default selection of Database on the Choose A Data Source Type page,

as shown in Figure 7-3 Then, click Next

Figure 7-3 The Choose a Data Source Type page of the Data Source Configuration Wizard

4 The list box displays the available data connections from Server Explorer Select

a connection to the Northwind sample database or create a new data connection

on the Choose Your Data Connection page, as shown in Figure 7-4 Then, click Next If prompted, click Yes to add the database to your project

Figure 7-4 The Choose Your Data Connection page of the Data Source Configuration Wizard

5 After selecting the desired data connection, you are given the option of saving it

to the application configuration file Leave the default option selected, as shown

in Figure 7-5 Then, click Next

Figure 7-5 The Save the Connection String to the Application Configuration File page of the

Data Source Configuration Wizard

6 Expand the Tables node and select the Customers table on the Choose Your

Database Objects page, as shown in Figure 7-6

Figure 7-6 The Choose Your Database Objects page of the Data Source Configuration Wizard

7 Click Finish to complete the wizard and add the typed DataSet to your project

After completing the wizard, the data source is available in the Data Sources win­dow, which enables the quick construction of data-bound forms

8 With Form1 in Design view, select Show Data Sources from the Data menu

9 Drag the Customers node from the Data Sources window onto Form1, as shown

10 Run the application and verify that the Customers table data appears on the

form, as shown in Figure 7-8

Figure 7-8 The Customers data displayed on Form1

� Exercise 3: Configuring Untyped DataSet Objects

Create untyped DataSet objects by dragging DataSet objects from the Toolbox onto a

form

1 Create a Windows application and name it UntypedDataSet

2 From the Data section of the Toolbox, drag a DataSet object onto Form1

3 In the Add DataSet dialog box, select Untyped DataSet and click OK

4 Drag a DataGridView onto the form

5 Select the DataSet1 instance in the component tray and navigate to the Tables

property in the Properties window Click the ellipsis in the Tables property to

open the Tables Collection Editor

6 Add a table and set its Name and TableName properties to Categories

7 Select the Columns property and click the ellipsis to open the Columns Collec­

11 Select the CategoryID column and the Primary key check box and click OK

12 Close the Constraints Collection Editor and the Tables Collection Editor

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

❑ Name = FillDataSetButton

❑ Text = Fill DataSet

14 Create a Form1_Load event handler and add the following code:

16 With Form1 in Design view, select DataSet1 in the component tray

17 From the Tables property in the Property window, open the Tables Collection

Editor and add another table to the DataSet

18 Set its Name and TableName properties to Products

19 Add a column and set the following properties:

❑ AllowDBNull = False

❑ AutoIncrement = True

❑ ColumnName = ProductID

23 Select the ProductID column and the Primary key check box and click OK

24 Add a Foreign Key Constraint and set the following:

❑ Parent table = Categories

❑ Child table = Products

❑ Key columns = CategoryID

❑ Foreign Key columns = CategoryID

25 Click OK

26 Close the Collection Editors, and then close the Table Collection Editor

27 Select DataSet1 in the component tray and add a DataRelation by clicking the

ellipsis in the Relations property of DataSet1

28 Click Add in the Relations Collection Editor Set the following in the Relations

dialog box:

❑ Name = CategoriesProducts

❑ Parent table = Categories

❑ Child table = Products

❑ Key columns = CategoryID

❑ Foreign Key columns = CategoryID

29 Close the dialog boxes

30 Add the following code to the bottom of the FilllDatasetButton_Click event handler:

' VB

// C#

31 Create an event handler for the DataGridView1_CellDoubleClick event and add

the following code:

33 Now double-click one of the categories in the grid to open a message box dis­

playing the related products

■ Untyped and typed DataSet objects can be created by dragging a DataSet object

from the data Toolbox onto a form

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 What is a DataSet? (Choose all that apply.)

A A pointer to a remote database

B A collection of DataTable and DataRelation objects

C An in-memory cache of data

D A collection of records from a database

2 What are the three main objects when working with a DataSet?

A DataTable, DataRelation, and DataAdapter

B DataTable, DataColumn, and DataRelation

C DataTable, DataRelation, and Constraint

D DataTable, DataColumn, and type

3 How do you programmatically access related records in a DataSet?

A By calling the GetParentRow and GetChildRows methods of a DataSet

B By calling the GetParentRow and GetChildRows methods of a DataTable

C By calling the GetParentRow and GetChildRows methods of a DataRow

D By accessing the ParentColumns and ChildColumns of a DataRelation

Lesson 2: Creating DataTable Objects

This lesson describes how to create DataTable objects, which are ADO.NET objects in the System.Data namespace that provide in-memory storage for the data in your appli­ cation similar to a table in a database DataTable objects can be added to DataSet objects and related to other DataTable objects using a DataRelation object, or you can use DataTable objects as standalone objects independent of DataSet objects

Once a DataTable object is created, define the schema of the table by creating and add­

ing columns and constraints similar to tables in a database This lesson will focus on

creating and configuring the DataTable, preparing it to receive data The process of fill­ ing the DataTable with data, as well as manipulating the data in the table, will be cov­

ered later in this chapter

After this lesson, you will be able to:

■ Create DataTable objects

❑ Create a DataTable

❑ Add a DataTable to a DataSet

❑ Define the schema of a DataTable

❑ Add columns to a table

❑ Create expression columns

❑ Create AutoIncrementing columns

❑ Define a primary key for a table

❑ Add constraints to a table

Estimated lesson time: 45 minutes

How to Create DataTable Objects

Create DataTable objects by declaring an instance of the DataTable object You can optionally provide the name of the DataTable as well as the Namespace that will be

used when rendering the data in XML For example, the following code example cre­

ates a new DataTable named SalesData: