1. Microsoft Visual Basic 2010: Reloaded Fourth Edition
Chapter Twelve
Access Databases and LINQ

2. Objectives After studying this chapter, you should be able to:
Define the terms used when talking about databases
Connect an application to a Microsoft Access database
Bind table and field objects to controls
Explain the purpose of the DataSet, BindingSource, TableAdapter, TableAdapterManager, and BindingNavigator objects
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

3. Objectives (cont'd.) Customize a DataGridView control
Handle errors using the Try…Catch statement
Position the record pointer in a dataset
Access the value stored in a field object
Query a dataset using LINQ
Customize a BindingNavigator control
Use the LINQ aggregate methods
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

4. Database Terminology
Computer database: electronic file containing an organized collection of related information
Relational database: database that stores information in tables composed of columns and rows
Field: single item of information
Record: group of related fields
Table: group of related records
Primary key: field that uniquely identifies each record
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

5. Database Terminology (cont'd.)
Figure 12-1: Example of a one-table relational database
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

6. Database Terminology (cont'd.)
Parent table: contains a primary key
Child table: contains a foreign key from the parent table to link the tables
Foreign key: field in a table that contains the primary key of another table
Relational database advantages:
Less redundancy
Fast retrieval
Ability to selectively retrieve data
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

7. Database Terminology (cont'd.)
Figure 12-2: Example of a two-table relational database
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

8. Connecting an Application to a Microsoft Access Database
Has a file extension of .accdb
Must connect an application to the database before the application can access the data
Use the Data Source Configuration Wizard to connect to a database
Dataset: copy of the fields and records stored in the computer’s internal memory, which the application can access
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

9. Connecting an Application to a Microsoft Access Database (cont'd.)
Figure 12-3: Data contained in the tblEmploy table
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

10. Connecting an Application to a Microsoft Access Database (cont'd.)
Figure 12-4: How to connect an application to an Access database
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

11. Connecting an Application to a Microsoft Access Database (cont'd.)
Figure 12-5: Result of running the Data Source Configuration Wizard
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

12. Connecting an Application to a Microsoft Access Database (cont'd.)
Figure 12-6: How to preview the contents of a dataset
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

13. Figure 12-7: EmployeesDataSet shown in the Preview Data dialog box
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

14. Binding the Objects in a Dataset
Binding: connecting an object in a dataset to a control on a form
Bound controls: controls that are connected to an object in a dataset
Can bind an object to:
An existing control in the interface
A control the computer creates for you
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

15. Binding the Objects in a Dataset (cont'd.)
Figure 12-8: How to bind an object in a dataset
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

16. Having the Computer Create a Bound Control
To allow the computer to create a bound control:
Drag the object from the dataset to the form
DataGridView control: displays table data in a row and column format
Use the list arrow next to an object’s name to change the type of control to be created
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

17. Having the Computer Create a Bound Control (cont'd.)
Figure 12-9: Icons in the Data Sources window
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

18. Having the Computer Create a Bound Control (cont'd.)
Figure 12-10: Result of clicking the tblEmploy table object’s list arrow
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

19. Having the Computer Create a Bound Control (cont'd.)
Figure 12-11: Result of clicking the Last_Name filed object’s list arrow
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

20. Having the Computer Create a Bound Control (cont'd.)
BindingNavigator control:
Allows movement to first, last, next, or previous record
Allows direct selection of record by number
Allows you to add or delete a record
Allows you to save changes made to the dataset
Five objects are placed in the component tray:
DataSet, BindingSource, TableAdapter, TableAdapterManager, BindingNavigator
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

21. Having the Computer Create a Bound Control (cont'd.)
Figure 12-12: Result of dragging the table object to the form
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

22. Having the Computer Create a Bound Control (cont'd.)
TableAdapter object: connects the database to the DataSet object
DataSet object: stores the information to be accessed from the database
TableAdapterManager object: handles saving data to multiple tables in the DataSet
BindingSource object: connects the DataSet object to the bound controls on the form
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

23. Having the Computer Create a Bound Control (cont'd.)
Figure 12-13: Illustration of the relationships among the database, the objects in the component tray, and the bound controls
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

24. The DataGridView Control
DataGridView control: displays data in a row and column format
Each row represents a record
Each column represents a field
Cell: the intersection of a row and column
DataGridView has a task list used to control its appearance and behavior
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

25. The DataGridView Control (cont'd.)
Figure 12-14: Task list for a DataGridView control
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

26. The DataGridView Control (cont'd.)
Figure 12-15: Purpose of each task in the DataGridView’s task list
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

27. The DataGridView Control (cont'd.)
Figure 12-15: Edit Columns dialog box
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

28. The DataGridView Control (cont'd.)
Many properties of DataGridView are listed only in the Properties window
AutoSizeColumnsMode property:
Select Fill setting to automatically adjust column widths to exactly fill the display area
Select ColumnHeader setting to adjust column widths based on the header text
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

29. The DataGridView Control (cont'd.)
Figure 12-17: DataGridView control after setting some of its properties
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

30. Visual Basic Code
DataGridView control allows data to be edited directly within the control to update the database
Two event procedures are automatically created in Code Editor window when a table or field object is dragged to the form
MainForm_Load
bindingNavigatorSaveItem_Click
MainForm_Load event:
Fill method: TableAdapter object’s method to retrieve data from the database and store it in the dataset
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

31. Visual Basic Code (cont'd.)
bindingNavigatorSaveItem_Click event:
Saves any changes made to the dataset
EndEdit method: applies pending changes to the dataset
UpdateAll method: commits the dataset changes to the database
Be sure to use error-handling code
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

32. Visual Basic Code (cont'd.)
Figure 12-18: Code automatically entered in the Code Editor window
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

33. Handling Errors in the Code
Exception: an error that occurs while an application is running
VB “handles” errors if the program does not by showing an error message and terminating the application
Try…Catch statement: used to trap errors and attempt to handle them
Place code that could cause an exception within the Try block
Catch block is executed if an exception occurs
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

34. Figure 12-19: How to use the Try…Catch statement
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

35. Handling Errors in the Code (cont’d.)
Figure 12-19: How to use the Try…Catch statement (cont’d.)
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

36. Handling Errors in the Code (cont'd.)
Figure 12-20: Try…Catch statement entered in the Save Data button’s Click event procedure
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

37. Handling Errors in the Code (cont'd.)
Figure 12-21: Sample run of the Morgan Industries application
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

38. Handling Errors in the Code (cont'd.)
BindingNavigator control provides buttons for first, last, previous, and next record and for adding records, deleting records, and saving changes
Can also use the control to access a record by its record number
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

39. The Copy to Output Directory Property
Local database file: database file contained in a project
Copy to Output Directory property: determines how VB saves changes to a local database file
Copy always setting: database file is copied from the project folder to bin\Debug folder each time the application is started
Changes are made only to the bin\Debug copy
Copy if newer setting: newer of the two database files (project folder and bin\Debug folder) is saved in bin\Debug folder
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

40. The Copy to Output Directory Property (cont’d.)
Figure 12-22: How to use the Copy to Output Directory property
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

41. Binding to an Existing Control
Can bind an object in a dataset to an existing control in two ways:
Drag an object in the dataset to a control on the form
Select the control and set properties
Properties to bind the control are specific to the control
DataSet, BindingSource,TableAdapter, and TableAdapterManager objects are added to the component tray
BindingNavigator control is NOT added automatically
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

42. Binding to an Existing Control (cont'd.)
Figure 12-23: Result of dragging field objects to existing label controls
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

43. Binding to an Existing Control (cont'd.)
Figure 12-24: Sample run of a different version of the Morgan Industries application
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

44. Coding the Next Record and Previous Record Buttons
BindingSource object uses an invisible record pointer to track the current record in the dataset
Position property: stores position of current record; this position number is zero-relative
Move method: moves the record pointer’s position to first, last, previous, or next record in the dataset
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

45. Figure 12-23: How to use the BindingSource object’s Position property
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

46. Figure 12-26: How to use the BindingSource object’s Move methods
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

47. Coding the Next Record and Previous Record Buttons (cont'd.)
Figure 12-27: Code entered in the Click event procedures for the Next Record and Previous Record buttons
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

48. Accessing the Value Stored in a Field
Figure 12-28: How to access the value stored in a field object
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

49. Creating a Query Can arrange records in a dataset in any order
Query: specifies the records to select in a dataset
Language Integrated Query (LINQ): language used to create a query
Where clause: optional, specifies a condition to limit which records to view
Order By clause: optional, specifies whether to arrange in descending or ascending order
Option Infer On: allows computer to infer the data type from the variables in the query
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

50. Creating a Query (cont’d.)
Figure 12-29: How to use LINQ to select and arrange records in a dataset
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

51. Figure 12-29: How to use LINQ to select and arrange records in a dataset (cont’d.)
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

52. Creating a Query (cont’d.)
Figure 12-30: How to assign a LINQ variable’s contents to a BindingSource control
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

53. Figure 12-31: LINQ code entered in the Find Last Name button’s Click event procedure
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

54. Creating a Query (cont’d.)
Figure 12-32: Employees whose last name begins with the letter S
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

55. Personalizing a BindingNavigator Control
You can include other items on the BindingNavigator control:
Buttons, text boxes, or drop-down buttons
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

56. Personalizing a BindingNavigator Control (cont’d.)
Figure 12-33: How to manipulate the items on a BindingNavigator control
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

57. Personalizing a BindingNavigator Control (cont’d.)
Figure 12-34: Items Collection Editor window
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

58. Personalizing a BindingNavigator Control (cont’d.)
Figure 12-35: DropDownButton added to the BindingNavigator control
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

59. Using the LINQ Aggregate Operators
Aggregate operator: returns a single value from a group of values
Most commonly used aggregate operators:
Average, Count, Max, Min, and Sum
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

60. Figure 12-36: How to use the LINQ aggregate operators
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

61. Using the LINQ Aggregate Methods (cont'd.)
Figure 12-37: Code associated with the three items on the DropDownButton
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

62. Using the LINQ Aggregate Methods (cont'd.)
Figure 12-37: Code associated with the three items on the DropDownButton (cont’d.)
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

63. Using the LINQ Aggregate Methods (cont'd.)
Figure 12-37: Code associated with the three items on the DropDownButton (cont’d.)
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

64. Adding Items to the BindingNavigator Control (cont'd.)
Figure 12-38: Average pay rate for part-time employees
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

65. Programming Tutorial 1 Creating the Trivia Game application
Figure 12-40: MainForm for the Trivia Game application
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

66. Programming Tutorial 2 Creating the CD Collection application
Figure 12-50: Preview Data dialog box showing the data stored in the CDDataSet
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

67. Programming Example Cartwright Industries application
Figure 12-55: MainForm in the Cartwright Industries application
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

68. Summary Can use Visual Basic to access data stored in databases
Relational database: stores information in tables composed of fields and records
Primary key: field in a database table that uniquely identifies each record
Data in a relational database can be displayed in any order, and you can control the amount of information to view
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

69. Summary (cont'd.)
You must connect the application to a database to create a dataset
Display dataset information by binding controls to dataset objects
TableAdapter: connects a database to a DataSet object
BindingSource object: connects a DataSet object to bound controls on a form
DataGridView control displays data in row and column format
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

70. Summary (cont'd.) Use a Try…Catch statement to handle exceptions
Database file’s Copy to Output Directory property: determines when and if the file is copied to the project’s bin\Debug folder
BindingSource object’s Position property: stores the location of the record pointer in a dataset
BindingSource object’s Move methods: used to move the record pointer in a dataset
Can access the value stored in a field object in a dataset
Microsoft Visual Basic 2010: Reloaded, Fourth Edition

71. Summary (cont'd.) Use LINQ to select and arrange records in a dataset
LINQ provides Average, Sum, Count, Min, and Max aggregate methods
Can include additional items such as text boxes and drop-down buttons on a BindingNavigator control
Microsoft Visual Basic 2010: Reloaded, Fourth Edition