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Chapter 10, Slide 3 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 4 Starting Out with Visual Basic 3rd Edition
Section 10.1What Is a Database?
A Database is a Collection of Data Organized in Tables, Rows, and Columns
Chapter 10, Slide 5 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 6 Starting Out with Visual Basic 3rd Edition
Database Table
Row(Record)
Column Field
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
Chapter 10, Slide 7 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 Long
Date/Time Date, DateTime
Number, Integer Integer
Number, long integer Long Integer
Number, single Single
Number, double Double
Text String
Yes/No Boolean
Chapter 10, Slide 8 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 Text 40Last_Name Text 40Phone Text 30Email Text 40Date_Joined Date/TimeOfficer Yes/No 1
Chapter 10, Slide 9 Starting Out with Visual Basic 3rd Edition
Issues with Redundant Data Database design minimizes redundant data In the following employee table:
ID First_Name Last_Name Department001234 Ignacio Fleta Accounting002000 Christian Martin Computer Support002122 Orville Gibson Human Resources00300 Jose Ramirez Research & Devel003400 Ben Smith Accounting003780 Allison Chong 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 10 Starting Out with Visual Basic 3rd Edition
Eliminating Redundant Data Create a department table
Dept_ID Dept_Name Num_Employees1 Human Resources 102 Accounting 53 Computer Support 304 Research & Development 15
Reference department table in employee tableID First_Name Last_Name Dept_ID001234 Ignacio Fleta 2002000 Christian Martin 3002122 Orville Gibson 1003000 Jose Ramirez 4003400 Ben Smith 2003780 Allison Chong 3
Chapter 10, Slide 11 Starting Out with Visual Basic 3rd Edition
One-to-Many Relationships
The previous changes created a one-to-many 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 12 Starting Out with Visual Basic 3rd Edition
Section 10.2Using 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 13 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 14 Starting Out with Visual Basic 3rd Edition
Connecting VB to a Database
The flow of data from database to 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
DataSource
BindingSource
TableAdapter Dataset Application
Chapter 10, Slide 15 Starting Out with Visual Basic 3rd Edition
Section 10.3Selecting Dataset Rows
Visual Basic Provides Convenient Tools for Selecting Which Rows from the Dataset You Want to Display
Chapter 10, Slide 16 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 17 Starting Out with Visual Basic 3rd Edition
SQL Query Example
You might want to select all employees hired before 1998 and earning less than $45,000Select ID, Name, Full_Time, Hire_Date, SalaryFrom employeesWhere 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 18 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 19 Starting Out with Visual Basic 3rd Edition
Section 10.4Data-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 21 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 22 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 23 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 24 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 25 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.PaymentsRowRow = CType(DsPayments.Payments.NewRow(), _
dsPayments.PaymentsRow)With rowrow.Member_ID = 5row.Payment_Date = #5/15/2006#row.Amount = 500D
End WithDsPayments.Payments.Rows.Add(row)
Chapter 10, Slide 26 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 27 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 28 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 29 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.PaymentsRowDim decTotal as Decimal = 0For Each row in DsPayments.Payments.Rows
decTotal += row.AmountNext
Tutorial 10-5 demonstrates this technique
Chapter 10, Slide 30 Starting Out with Visual Basic 3rd Edition
Section 10.5Structured Query Language
(SQL)
SQL Is a Standard Language for Working With Databases
Chapter 10, Slide 31 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-listFrom table
• column-list contains column names to select from table, each separated by a comma
The following Select statement retrieves the ID and Salary fields from the SalesStaff tableSelect ID, SalaryFrom SalesStaff
Chapter 10, Slide 32 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_HiredFrom SalesStaff
Chapter 10, Slide 33 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_NameFrom 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 payAmountFrom Payroll
• Creates a payAmount column with gross pay
Chapter 10, Slide 34 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 DescOrder by Last_Name DESC
Order By clause appears after From clauseSelect First_Name, Last_Name, Date_JoinedFrom MembersOrder By Last_Name, First_Name
• Lists all members by last name, then first
Chapter 10, Slide 35 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 payAmountFrom PayrollWhere payAmount > 1000Order by Last_Name
• Selects those being paid more than $1,000
Chapter 10, Slide 36 Starting Out with Visual Basic 3rd Edition
SQL Relational Operators SQL Where uses relational operators just like a VB If
Operator Meaning= equal to
<> not equal to< less than
<= less than or equal to> greater than
>= greater than or equal toBetween between two values (inclusive)
Like 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 37 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 $40,000Where (Hire_Date > #1/1/1990#) and (Salary > 40000)
Select all employees hired after 1/1/1990 or with a salary is greater than $40,000Where (Hire_Date > #1/1/1990#) or (Salary > 40000)
Select employee names not beginning with AWhere Last_Name Not Like ‘A%’