Transcript Starting Out With Visual Basic

Chapter 10
Working With Databases
Chapter 10, Slide 1
Starting Out with Visual Basic 3rd Edition
Chapter 10
Introduction
Chapter 10, Slide 2
Starting Out with Visual Basic 3rd Edition
Chapter 10 Topics





Basic database terminology
Fundamental database concepts
Use ADO .NET to access databases
Display, sort, and update database data
Use the DataGridView control
Chapter 10, Slide 3
Starting Out with Visual Basic 3rd Edition
Section 10.1
What Is a Database?
A Database is a Collection of Data Organized in Tables,
Rows, and Columns
Chapter 10, Slide 4
Starting Out with Visual Basic 3rd Edition
Terminology
 Database: a collection of interrelated tables
 Table: a logical grouping of related data
• A category of people, places, or things
• For example, employees or departments
• Organized into rows and columns
 Field: an individual piece of data pertaining to
an item, an employee name for instance
 Record: the complete data about a single item
such as all information about an employee
• A record is a row of a table
Chapter 10, Slide 5
Starting Out with Visual Basic 3rd Edition
Database Table
 Each table has a primary key
• Uniquely identifies that row of the table
• PartNumber is the primary key in this example
 Columns also called fields or attributes
 Each column has a particular data type
Row
(Record)
Column
Chapter 10, Slide 6
Field
Starting Out with Visual Basic 3rd Edition
VB and Access Data Types
 VB data types must match table data types
 MS Access and VB have similar data types
Access Data Type
Visual Basic Data Type
AutoNumber
Date/Time
Number, IntegerInteger
Number, long integer
Number, single
Number, double
Text
Yes/No
Long
Date, DateTime
Chapter 10, Slide 7
Long Integer
Single
Double
String
Boolean
Starting Out with Visual Basic 3rd Edition
Database Design
 A database schema is the design of tables,
columns, and relationships between tables
 Define a column for each piece of data
 Allow plenty of space for text fields
 For the members of an organization:
Column Name
Type
Size
First_Name
Last_Name
Phone
Email
Date_Joined
Officer
Text
Text
Text
Text
Date/Time
Yes/No
40
40
30
40
Chapter 10, Slide 8
1
Starting Out with Visual Basic 3rd Edition
Issues with Redundant Data
 Database design minimizes redundant data
 In the following employee table:
ID
001234
002000
002122
00300
003400
003780
First_Name
Ignacio
Christian
Orville
Jose
Ben
Allison
Last_Name
Fleta
Martin
Gibson
Ramirez
Smith
Chong
Department
Accounting
Computer Support
Human Resources
Research & Devel
Accounting
Computer Support
 Same dept name appears multiple times
• Requires additional storage space
• Causes problems if misspelled
• What if a department needs to be renamed?
Chapter 10, Slide 9
Starting Out with Visual Basic 3rd Edition
Eliminating Redundant Data
 Create a department table
Dept_ID
1
2
3
4
Dept_Name
Human Resources
Accounting
Computer Support
Research & Development
Num_Employees
10
5
30
15
 Reference department table in employee table
ID
001234
002000
002122
003000
003400
003780
Chapter 10, Slide 10
First_Name
Ignacio
Christian
Orville
Jose
Ben
Allison
Last_Name
Fleta
Martin
Gibson
Ramirez
Smith
Chong
Dept_ID
2
3
1
4
2
3
Starting Out with Visual Basic 3rd Edition
One-to-Many Relationships
 The previous changes created a one-tomany relationship
•
•
•
•
Every employee has one and only one dept
Every department has many employees
DeptID in department table is a primary key
DeptID in employee table is a foreign key
 In general, a one-to-many relationship is
created when the primary key of one table is
specified as a field of a another table
Chapter 10, Slide 11
Starting Out with Visual Basic 3rd Edition
Section 10.2
Using the DataGridView
The DataGridView Control Allows you to Display a Database
Table in a Grid Which Can be Used at Runtime to Sort and Edit
the Contents of the Table
Chapter 10, Slide 12
Starting Out with Visual Basic 3rd Edition
Connecting VB to a Database
 VB provides tools to display database tables
 Data binding links tables to form controls
• Controls called components establish the link
• A wizard guides you through the process
 We’ll use these data-related components:
• Data source – usually a database
• Binding source – holds database name,
location, and other connection information
• Table adapter – uses SQL to select data
• Dataset – in-memory copy of data from tables
Chapter 10, Slide 13
Starting Out with Visual Basic 3rd Edition
Connecting VB to a Database
 The flow of data from database to application
Data
Source
•
•
•
•
Binding
Source
Table
Adapter
Dataset
Application
Note that data moves in both directions
Data travels from data source to application
Application can view/change dataset contents
Changes to dataset can be written back to
the data source
 Tutorial 10-1 demonstrates how to connect a
database table to a DataGridView control
Chapter 10, Slide 14
Starting Out with Visual Basic 3rd Edition
Section 10.3
Selecting Dataset Rows
Visual Basic Provides Convenient Tools for Selecting Which
Rows from the Dataset You Want to Display
Chapter 10, Slide 15
Starting Out with Visual Basic 3rd Edition
Structured Query Language (SQL)
 Often need to select certain rows in a table
using Structured Query Language (SQL)
•
•
•
•
Standard method of working with a database
Adopted by most all database software
Not a general purpose programming language
Defines how to construct queries that return
selected data from the database
Chapter 10, Slide 16
Starting Out with Visual Basic 3rd Edition
SQL Query Example
 You might want to select all employees hired
before 1998 and earning less than $45,000
Select ID, Name, Full_Time, Hire_Date, Salary
From employees
Where Hire_Date < 1/1/1998 and Salary < 45000
•
•
•
•
Select, From, and Where are keywords
Fields to be returned listed after Select
Table containing the data listed after From
Conditions affecting row selection after Where
 SQL query is a property of the TableAdapter
Chapter 10, Slide 17
Starting Out with Visual Basic 3rd Edition
Configuring the TableAdapter
 Right-click on dataset and select Configure to
start TableAdapter Configuration Wizard
• Can modify a simple query directly in wizard
• Or use Query Builder for more complex query
 Query Builder is a tool to create or modify
queries with minimal knowledge of SQL
 To add a query to a DataGridView
• Right-click Table Adapter icon attached to grid
• Select Add Query from shortcut menu
 Tutorial 10-2 demonstrates how this is done
Chapter 10, Slide 18
Starting Out with Visual Basic 3rd Edition
Section 10.4
Data-Bound Controls
Some Controls Can Be Bound to a Dataset. A Data-bound
Control Can be Used to Display and Edit the Contents of a
Particular Row and Co.lumn
Chapter 10, Slide 19
Starting Out with Visual Basic 3rd Edition
Chapter 10, Slide 20
Starting Out with Visual Basic 3rd Edition
Advantages of Data-Binding
 Can add multiple data sources to a project
 Can bind fields in a data source to controls:
• Text boxes
• Labels
• List boxes
 Contents of data-bound controls change
automatically when moving from row to row
 Updating the contents of a database field
from a data-bound control is also very easy
Chapter 10, Slide 21
Starting Out with Visual Basic 3rd Edition
Binding Existing Dataset to DataGrid
 Use the Data Sources window
• Locate the dataset table
• Drag table to an open area of a form
• Creates a data grid bound to the data source
 Automatically adds a navigation bar to form
 Set Dock property to Center Docking to make
the data grid fill the entire form
Chapter 10, Slide 22
Starting Out with Visual Basic 3rd Edition
Binding Individual Fields to Controls
 Use the Data Sources window
•
•
•
•
•




Locate the dataset table
Select Details from the table drop-down list
Drag table to an open area of a form
Creates a separate control for each field
Can also drag columns individually
Adds automatic navigation bar as before
Text and numeric fields added as text boxes
Yes/No fields added as checkboxes
May wish to change some control properties
Chapter 10, Slide 23
Starting Out with Visual Basic 3rd Edition
Binding to List and Combo Boxes
 List and combo boxes are frequently used to
supply a list of items for a user to select from
 Such lists are often populated from a table
 Must set two list/combo box properties
• DataSource identifies a table within a dataset
• DisplayMember identifes the table column to
be displayed in the list/combo box
 If table column dragged onto a list/combo box
• Visual Studio creates the required dataset,
table adapter, and binding source components
 Tutorial 10-3 shows this type of binding
Chapter 10, Slide 24
Starting Out with Visual Basic 3rd Edition
Adding New Rows to a Dataset




NewRow method creates a new, empty row
Assign values to columns in the empty row
Add method appends new row to the dataset
The following example adds a new row to the
Payments table of the dsPayments dataset
Dim row as dsPayments.PaymentsRow
Row = CType(DsPayments.Payments.NewRow(), _
dsPayments.PaymentsRow)
With row
row.Member_ID = 5
row.Payment_Date = #5/15/2006#
row.Amount = 500D
End With
DsPayments.Payments.Rows.Add(row)
Chapter 10, Slide 25
Starting Out with Visual Basic 3rd Edition
Another Means to Add Dataset Rows
 Can call the dataset Add method directly
 This approach is more straightforward but:
• Must specify values in correct column order
• Previous example becomes far simpler:
DsPayments.Payments.Rows.Add( _
Nothing, 5, #5/15/2006#, 500D)
 Payments table 1st column is autonumber so:
• Must have an argument for this column
• Pass Nothing as the value for this column
Chapter 10, Slide 26
Starting Out with Visual Basic 3rd Edition
Removing a Row from a Dataset
 Two steps to remove a row
• Get a reference to the row to remove
• Call Remove method on Rows collection
 Following example calls FindByID with the
primary key to get a reference to the row
Dim row as DataRow = _
DsPayments.Payments.FindByID(36)
DsPayments.Payments.Rows.Remove(row)
Chapter 10, Slide 27
Starting Out with Visual Basic 3rd Edition
Updating the Database
 Previous add and remove examples change
the dataset but not the underlying database
 Must call TableAdapter Update method to
save dataset changes to the database
 To write changes in the DsPayments dataset
to the underlying database:
PaymentsTableAdapter.Update(DsPayments)
 Tutorial 10-4 demonstrates adding new rows
to the Payments table
Chapter 10, Slide 28
Starting Out with Visual Basic 3rd Edition
Reading Dataset Rows with For-Each
 A For-Each statement can be used to iterate
over all rows of a dataset
 Usually use a strongly typed dataset for this
 Sum Amount column of dsPayments dataset
Dim row as dsPayments.PaymentsRow
Dim decTotal as Decimal = 0
For Each row in DsPayments.Payments.Rows
decTotal += row.Amount
Next
 Tutorial 10-5 demonstrates this technique
Chapter 10, Slide 29
Starting Out with Visual Basic 3rd Edition
Section 10.5
Structured Query Language
(SQL)
SQL Is a Standard Language for Working With Databases
Chapter 10, Slide 30
Starting Out with Visual Basic 3rd Edition
The Select Statement
 Select retrieves rows from one or more tables
in a database
• Basic form of Select for a single table is
Select column-list
From table
•
contains column names to select
from table, each separated by a comma
column-list
 The following Select statement retrieves the
ID and Salary fields from the SalesStaff table
Select ID, Salary
From SalesStaff
Chapter 10, Slide 31
Starting Out with Visual Basic 3rd Edition
Column Names
 Use asterisk to select all columns in a table
Select *
From SalesStaff
 Unlike VB names, SQL columns can have
embedded spaces
• If so, use square brackets around column names
Select [Last Name], [First Name]
From SalesStaff
• Better to avoid embedded spaces for this reason
 As operator can be used to rename columns
Select Last_Name, Hire_Date As Date_Hired
From SalesStaff
Chapter 10, Slide 32
Starting Out with Visual Basic 3rd Edition
Creating New Columns
 Sometimes useful to create a new column by
appending existing columns together
• Create a Full_Name field from first and last name
Select Last_Name + ‘, ‘ + First_Name as Full_Name
From SalesStaff
• Creates a Full_Name field in the format last, first
 Can also be useful to create a new column by
performing arithmetic operations
• Columns involved must be numeric
Select ID, hrsWorked * hourlyRate As payAmount
From Payroll
• Creates a payAmount column with gross pay
Chapter 10, Slide 33
Starting Out with Visual Basic 3rd Edition
Sorting Rows with Order By Clause
 SQL Select has an optional Order By clause
that affects the order in which rows appear
Order by Last_Name, First_Name
• Displays rows in order by last name, then first
• Sort in reverse order (high to low) using Desc
Order by Last_Name DESC
 Order By clause appears after From clause
Select First_Name, Last_Name, Date_Joined
From Members
Order By Last_Name, First_Name
• Lists all members by last name, then first
Chapter 10, Slide 34
Starting Out with Visual Basic 3rd Edition
Selecting Rows with Where Clause
 SQL Select has an optional Where clause that
can be used to select (or filter) certain rows
Where Last_Name = ‘Gomez’
• Displays only rows where last name is Gomez
• Must be a defined column (in table or created)
 This example selects based on a created field
Select Last_Name, hrsWorked * Rate As payAmount
From Payroll
Where payAmount > 1000
Order by Last_Name
• Selects those being paid more than $1,000
Chapter 10, Slide 35
Starting Out with Visual Basic 3rd Edition
SQL Relational Operators
 SQL Where uses relational operators just like a VB If
Operator
Meaning
=
<>
<
<=
>
>=
Between
Like
equal to
not equal to
less than
less than or equal to
greater than
greater than or equal to
between two values (inclusive)
similar to (match using wildcard)
 Example of Between operator:
Where Hire_Date Between #1/1/1992# and #12/31/1999#
 Example of Like operator with % sign as wildcard:
Where Last_Name Like ‘A%’
Chapter 10, Slide 36
Starting Out with Visual Basic 3rd Edition
Compound Expressions
 SQL uses And, Or, and Not to create
compound expressions
 Select all employees hired after 1/1/1990 and
with a salary is greater than $40,000
Where (Hire_Date > #1/1/1990#) and (Salary > 40000)
 Select all employees hired after 1/1/1990 or
with a salary is greater than $40,000
Where (Hire_Date > #1/1/1990#) or (Salary > 40000)
 Select employee names not beginning with A
Where Last_Name Not Like ‘A%’
Chapter 10, Slide 37
Starting Out with Visual Basic 3rd Edition
Section 10.6
Karate School
Management Application
Create an Application that Works With the
Karate School Database
Chapter 10, Slide 38
Starting Out with Visual Basic 3rd Edition