Download Chapter12 Access databases

Microsoft Visual Basic 2010:
Reloaded
Fourth Edition
Chapter Twelve
Access Databases and LINQ
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
2
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
3
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
4
Database Terminology (cont'd.)
Figure 12-1: Example of a one-table relational database
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
5
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
6
Database Terminology (cont'd.)
Figure 12-2: Example of a two-table relational database
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
7
Connecting an Application to a
Microsoft Access Database
• 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
8
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
9
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
10
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
11
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
12
Figure 12-7: EmployeesDataSet shown in the Preview Data dialog box
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
13
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
14
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
15
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
16
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
17
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
18
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
19
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
20
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
21
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
22
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
23
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
24
The DataGridView Control (cont'd.)
Figure 12-14: Task list for a DataGridView control
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
25
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
26
The DataGridView Control (cont'd.)
Figure 12-15: Edit Columns dialog box
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
27
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
28
The DataGridView Control (cont'd.)
Figure 12-17: DataGridView control after setting some of its properties
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
29
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
30
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
31
Visual Basic Code (cont'd.)
Figure 12-18: Code automatically entered in the Code Editor window
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
32
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
33
Figure 12-19:
How to use the
Try…Catch
statement
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
34
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
35
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
36
Handling Errors in the Code (cont'd.)
Figure 12-21: Sample run of the Morgan Industries application
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
37
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
38
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
39
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
40
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
41
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
42
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
43
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
44
Figure 12-23: How to use the BindingSource object’s Position property
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
45
Figure 12-26: How to use the BindingSource object’s Move methods
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
46
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
47
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
48
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
49
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
50
Figure 12-29:
How to use
LINQ to
select and
arrange
records in a
dataset
(cont’d.)
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
51
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
52
Figure 12-31: LINQ code entered in the Find Last Name button’s
Click event procedure
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
53
Creating a Query (cont’d.)
Figure 12-32: Employees whose last name begins with the letter S
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
54
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
55
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
56
Personalizing a BindingNavigator
Control (cont’d.)
Figure 12-34: Items Collection Editor window
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
57
Personalizing a BindingNavigator
Control (cont’d.)
Figure 12-35: DropDownButton added to the BindingNavigator control
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
58
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
59
Figure 12-36: How to
use the LINQ
aggregate operators
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
60
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
61
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
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
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
64
Programming Tutorial 1
• Creating the Trivia Game application
Figure 12-40: MainForm for the Trivia Game application
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
65
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
66
Programming Example
• Cartwright Industries application
Figure 12-55: MainForm in the Cartwright Industries application
Microsoft Visual Basic 2010: Reloaded, Fourth Edition
67
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
68
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
69
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
70
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
71