programming with microsoft visual basic 2008 fourth edition chapter thirteen working with access...

Programming with Microsoft Visual Basic 2008

Fourth Edition

Chapter Thirteen

Working with Access Databases and LINQ

Previewing the Paradise Bookstore Application

• Open the Chap13\Paradise.exe file

(Need to download Books.accdb Access DB too.)

• Application displays records in the Books database

• Allows the store manager to enter an author’s name (or part of a name) – Displays only books written by the author

• Displays the total value of books in the store

Programming with Microsoft Visual Basic 2008, Fourth Edition 2

GUI Introduction

Previewing the Paradise Bookstore Application (continued)


Figure 13-1: Books written by Carol Smith

Lesson A Objectives

After studying Lesson A, you should be able to: • Understand database terms • Connect an application to a Microsoft Access D/B• Bind table and field objects to VB controls• Explain the purpose of VB database objects

– DataSet, BindingSource, – TableAdapter, TableAdapterManager, – BindingNavigator

• Customize a DataGridView control• Handle errors using the Try…Catch statement• Position the record pointer in a dataset


Database Terminology

• Computer database: Electronic file containing an organized collection of related information

• Relational database: Database that stores information in tables composed of rows and columns

– Each column (直欄 ) in a table represents a field

– Each row (橫列 ) in a table represents a record

• Field: Single piece of information about an object, e.g., person, place or thing, …


Database Terminology (continued)

• Record: A group of related fields that contain all the necessary data about a specific object (person, place, or thing, …)

• Table: A group of similar records

– Each record in a table pertains to the same topic, and contains the same type of information

• Primary key: A field uniquely identifying a record

• Foreign key: Field that links a child record to a parent record in a 1:M relationship



Figure 13-2: Example of a relational table

Example of a relational table


Figure 13-3: Example of PK-FK pair in parent/child tables

Example of PK-FK pair in a 1:M relationship

Connecting an Application to a Microsoft Access Database

• MS Access 2007 database has a file extension of .accdb (Need to install Access 2007 Database Engine Driver in PC)

• Sample database contains one table named tblEmploy, containing employee information

• A VB application must create a database connection to access data

• Data Source Configuration Wizard (資料來源組態精靈 )

– Helps you connect an application to a database

• Dataset: A temporary copy of the data you have requested from the database



Figure 13-4: Data contained in the tblEmploy table


(Table example)


(continued)In Visual Studio, perform the following steps:1. Open the Server Explorer window: Click the View

menu and then click Server (Database) Explorer

2. Click the Data menu and then click Show Data Sources to open Data Sources window

3. Click Add New Data Source button, and then select Database

4. Click New Connection button, and then select Microsoft Access Database File (OLE DB)

5. Click Browse, navigate to database file, and then click Open



(continued)


1.2

2.2

3.1

3.2

2.11.1

Connecting an Application to a Microsoft Access Database (Data Source Configuration Wizard)


4.1


• In Visual Studio, perform these steps (continued):

6. Click button on Add Connection screen, and if successful, click Next

(May need to install Access 2007 Database Engine Driver)

7. Click button to include the database file into the current project

8. Click Yes to save connection string

9. On Choose Your Database Objects screen, select all table objects

10.Finish


Test Connection

Yes


Figure 13-6: Completed Add Connection dialog box


(Test Connection )

5

4.2


Figure 13-7: Message regarding copying the database file


(continued)


Figure 13-8: Save the Connection String to the Application Configuration File screen


(save connection string)


Figure 13-9: Objects selected in the Choose Your Database Objects screen

Connecting an Application to a Microsoft Access Database (Choose Your Database Objects )


Figure 13-10: Result of running the Data Source Configuration Wizard


(continued)

Previewing the Contents of a Dataset

1. Click the form to make it the active window

2. Click Data menu and then click Preview Data to

open Preview Data dialog box

3. Select the object to preview and then click

Preview

4. After previewing the data, click Close button

Check how many new files show up in Morgan

Industries Project


Binding the Objects in a Dataset

• Must bind one or more objects in the dataset to

controls in the interface to view dataset contents

• Binding: Connecting a dataset object to a

control

• Bound controls: Connected controls

• Types of controls used to bind dataset objects:

– Computer-created control

– Existing control on the form



Figure 13-12: Ways to bind an object in a dataset

Binding the Objects in a Dataset (continued)

1 Table Attribute

Having the Computer Create a Bound Control

• When you drag a dataset object onto a form:– Computer creates control (its type is indicated by

icon)

– Dataset object is automatically bound to control

• Example:– Drag tblEmployee table object to the form

– DataGridView control is created to display tabular data, with rows representing records, columns representing fields

• Use list arrow to change the type of control linked to the object


Table Attribute


Figure 13-13: Icons in the Data Sources window

Having the Computer Create a Bound Control (continued)


Figure 13-14: Result of clicking the tblEmploy object’s list arrow



Figure 13-15: Result of clicking the Last_Name object’s list arrow



Figure 13-16: Result of dragging the table object to the form



Figure 13-26: Data displayed in the DataGridView control

Running DataGridView


• In addition to a control, the computer adds:– BindingNavigator control: To move from one

record to the next in the dataset– TableAdapter object: Connects the database to

the DataSet object; responsible for retrieving data and storing it in the Dataset

– TableAdapterManager object: Handles saving data to multiple tables in the Dataset

– BindingSource object: Provides the connection between the Dataset and the bound controls



Figure 13-17: Illustration of the relationships among the database, the objects in the component tray, and the bound controls


located inmemory

located indisk

The DataGridView Control

• DataGridView control: Displays data in a row and column format

• Cell: Intersection of a row and column

• DataGridView’s task list

allows you to add, reorder, and remove columns, and set properties of bound columns

• AutoSizeColumnsMode: Has seven settings that control how the column widths are sized

– Fill setting: Automatically adjusts the column widths so that the display area of the control is filled



Figure 13-18: Task list for a DataGridView control

The DataGridView Control (continued)

DataGridView’s task list

To set the format of table columns


Figure 13-19: Purpose of each task in the DataGridView’s task list

The DataGridView Control (DataGridView’s task list)

常用

常用


Figure 13-20: Edit Column dialog box

The DataGridView Control (Edit Column dialog box)

1.1

1.2

2

3.1

Use Header Text to change the title of columns

3.2Use

DefaultCellStyle to set data format


Figure 13-21: Completed CellStyle Builder dialog box in DefaultCellStyle

The DataGridView Control (CellStyle Builder)


Figure 13-22: DataGridView control after setting some of its properties

The DataGridView Control (continued)

Visual Basic Code

• When a table or field object is dragged onto a

form the computer also enters code in the Code

Editor window

– Code in the form’s Load event uses the

TableAdapter object to retrieve data

– BindingNavigator’s save event is also coded



Figure 13-23: Code automatically entered in the Code Editor window

Visual Basic Code (continued)

A dataset defined In 資料來源

A table defined incertain dataset

Handling Errors in the Code

• Exception: Error that occurs while an application

is running

• Try…Catch statement: Used to intercept

exceptions and handle them

– Try block: Contains the statements that might fail

– Catch block: Contains the code to handle the

exceptions



Figure 13-24: Syntax and examples of the Try…Catch statement

Handling Errors in the Code (Try…Catch statement)


Figure 13-25: Try…Catch statement entered in the Save Data button’s Click event procedure

Handling Errors in the Code (continued)

Binding to an Existing Control

Can bind an object in a dataset to an existing control on the form in two ways:

•Method 1: Drag object from Data Sources window to control

•Method 2: Set one or more of the control’s properties in the Properties window

– Properties to set depend on the type of control being bound:

• DataGrid: Set DataSource and DataMember

• ListBox: Set DataSource and DisplayMember

• Label or text box: Set DataBindings and Text


Coding the Next Record and Previous Record Buttons

• BindingSource object’s Position property:

– Stores an invisible record pointer

– Positions are integer values 0

– First record is at position 0

• BindingSource object’s Move methods: Can be used to move the record pointer in a dataset to the first, last, next, or previous record in the dataset



Figure 13-29: Syntax and examples of the BindingSource object’s Position property


(continued)


Figure 13-29: Syntax and examples of the BindingSource object’s Position property (continued)


(continued)


Figure 13-29: Syntax and examples of the BindingSource object’s Move methods


(continued)


Figure 13-30: Code entered in each button’s Click event procedure


(continued)

Lesson A Summary

• Use Data Source Configuration Wizard to connect an application to a database

• Use the Preview Data command on the Data menu to preview the data in a dataset

• Bind an object in a dataset by dragging it to the form and letting the computer create a control, or by dragging it onto an existing control

• Use the Fill setting of the DataGridView’s AutoSizeColumnsMode property to have columns fill the display area


Lesson A Summary (continued)

• Use Dock property of DataGridView to anchor it

to the borders of form

• Use BindingSource object’s Position property or

its Move methods to move record pointer while

the application is running


Lesson B Objectives

After studying Lesson B, you should be able to:

• Query a dataset using LINQ

LINQ (Language INtegrated Query)

• Add an item to a BindingNavigator control

• Use the LINQ aggregate operators


Creating a Query

• Query: Specifies

– the records to select from a dataset, and

– the order in which to arrange the records

• Language Integrated Query (LINQ): A new database query language in Visual Basic 2008

– Where clause: Contains a condition to limit the records to be selected

– Order By clause: Used to arrange the records in ascending or descending order by one or more fields



Figure 13-32: Basic LINQ syntax and examples for selecting and arranging records

Creating a Query (continued)

Program

Block A

Each record in dataset.table is denoted by variable element in program block A

same record variable name


Figure 13-33: Code entered in the Declarations section and btnFind Click event procedure



Figure 13-33: Code entered in the Declarations section and btnFind Click event procedure (continued)


Customizing a BindingNavigator Control

• Can add additional items to a BindingNavigator

control to customize it:

– Button

– Textbox

– Drop-down button



Figure 13-35: Steps for adding an item to a BindingNavigator control

Customizing a BindingNavigator Control (continued)


Figure 13-36: Items Collection Editor dialog box

Customizing a BindingNavigator Control

(Items Collection Editor)An item’s property


Figure 13-37: DropDownButton added to the TblEmployBindingNavigator control

Customizing a BindingNavigator Control (continued)

Using the LINQ Aggregate Operators

• Aggregate operator:

Returns a single value from a group of values

• LINQ provides several aggregate operators:

– Average ( )

– Count ( )

– Max ( )

– Min ( )

– Sum ( )


Syntax of LINQ Aggregate Operators

Dim variable [As dataType] = Aggregate element In

dataset.table [Where condition] Select element.field

Into aggregateOperator()

Example 1

Dim dblAvgRate As Double _ = Aggregate employee In

EmployeeDataSet.tblEmployee _

Select employee.Rate _ Into Average( )


Examples of LINQ Aggregate Operators

Example 2

Dim dblMaxRate As Double _ = Aggregate employee In


Select employee.Rate _ Into Max( )

Example 3

Dim intCounter As Integer _ = Aggregate employee In


Select employee.Emp_Number _ Into Count( )



Figure 13-40: Message box showing the average pay rate for all employees

Using the LINQ Aggregate Operators (continued)

Lesson B Summary

• Use LINQ to select a range of records in a dataset

• You can customize the BindingNavigator control by adding additional items to it

• LINQ provides aggregate operators that return a single value from a group of values


Lesson C Objectives

After studying Lesson C, you should be able to:

• Prevent the user from adding and deleting

records

• Remove buttons from a BindingNavigator control

• Add a label, text box, and button to a

BindingNavigator control


Completing the Paradise Bookstore Application

• Requirements for Paradise Bookstore application: – Display records from the Books database– Allow store manager to enter an author’s name (or

part of a name) to display books by that author

• Database contains one table, tblBooks, with 5 fields and 11 records

• User should not be allowed to add or delete records– Must modify the BindingNavigatorControl to

remove the add and delete buttons


Completing the Paradise Bookstore Application (continued)


Figure 13-41: tblBooks table in the Books database

Completing the Paradise Bookstore Application (continued)


Figure 13-42: Completed TblBooksBindingNavigator control

Coding the Paradise Bookstore Application

• Go button’s Click event should display only records whose Author field starts with the characters entered in the txtAuthor text box

– If text box is empty, display all records

– Use the LINQ LIKE operator

• Total Value button’s Click event should display the total value of all books in the store

– Use the LINQ aggregate function SUM


Example

Example

Program

Program

Coding the Paradise Bookstore Application (continued)


Figure 13-43: Books written by authors whose name begins with s

Click Go1 2enter s

result 3



Figure 13-44: Message box showing the total value of the inventory

Click Go 1

2result


Figure 13-45: Click event procedures for the btnGo and btnTotal controls


Lesson C Summary

• Use the DataGridView control’s task box to

prevent the user from adding or deleting records

in the control

• Remove items from the BindingNavigator control

to prevent the user from performing some actions

• Can customize the BindingNavigator control by

adding a label, text box, or button to it


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