1. VB.NET
Using Database

2. Objectives Understand how VB .NET uses a database
Understand the basics of ADO.NET
Define a connection to a database
Use a DataAdapter to retrieve data from a database
Use the DataSet class
Bind controls to a DataSet
Use the ControlBindingsCollection
Understand how users navigate between records
Modify a database records
Count records
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3. Understanding How VB .NET Uses a Database
A database consists of information related to a particular topic or purpose
Information is organized into one or more tables
A table consists of rows and columns
Prefix for a table is "tbl"
A row is called a record
Each record contains multiple pieces of information
Each piece of information resides in a field
Prefix for a field is "fld"
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4. Characteristics of a Database
Many vendors supply databases
Oracle
Microsoft
SQL Server (More scaleable. Use with a large number of users)
Access (Use with just a few users)
Database are typically relational
Developers can relate information stored in tables in different ways
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5. Introduction to ADO.NET
The System.Data namespace provides access to database data
Collectively referred to as ADO.NET
ADO.NET is designed to work well with desktop and Internet applications
Works with different databases
Access, SQL Server
Uses a disconnected architecture
Note that ADO.NET and ADO are very different
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6. Establishing a Database Connection
ADO.NET Collection class forms a pipeline between your application and a data source by means of a provider
Two controls supply the connection
OleDbConnection control works with many databases
SQLConnection control works only with SQL server
Faster access
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7. OleDBConnection Class
Belongs to the System.Drawing.OleDB namespace
When creating an instance of the OleDbConnection control, VB .NET writes code to create an instance of the OleDbConnection class and configure it
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8. OleDbConnection Class Properties
ConnectionString property contains a string defining the database provider, database name, and security information
ConnectionTimeout property defines the number of seconds to wait for a connection to be established
DataSource property gets location and file name of the database
Provider property specifies property that will be used to establish the database connection
State property defines connection status (open, closed, etc.)
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9. OleDbConnection Class Methods and Events
Close method closes an open connection
Open method opens a closed connection
Uses the contents of ConnectionString property to open the connection
Events
StateChanged event fires when the connection state (State property) changes
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10. Connection Your solution ADO.NET connection Database provider database
Sends commands
Gets data
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11. Creating a Connection (Step 1)
Select Microsoft Jet 4.0 OLE DB Provider for Access databases
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12. Creating a Connection (Step 2)
Select database
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13. Code Behind a Database Connection
Provider key specifies the database provider
User ID and Password keys supply authentication information
Data Source key supplies database file
Mode key defines how database will be shared among connected users
Provider=Microsoft.Jet.OLEDB.4.0;Password="";User ID=Admin; Data Source=D:\VBOOP7\Chapter.08\Data\Employees.mdb; Mode=Share Deny None . . .
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14. The DataAdapter
Use the OleDBDataAdapter control to create a DataAdapter
Control supports a Wizard to help you configure the DataAdapter
Wizard writes code to create an instance of the OleDbDataAdapter class
Wizard writes SQL statements to select, update, and delete records
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15. The DataAdapter Class Properties Methods
SelectCommand property contains an SQL SELECT statement
InsertCommand, UpdateCommand, and DeleteCommand properties contain SQL INSERT, UPDATE, and DELETE statements
Methods
Fill method uses a connection to fill a DataSet with data
Update method sends changed data back to the DataSet
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16. Creating a Data Adapter (Step 1)
Create an instance of the OleDbDataAdapter control on the form
VB .NET activates the Wizard
Wizard starts by displaying an introductory screen
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17. Creating a Data Adapter (Step 2)
Add tables to the database
Select table(s) to use
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18. Creating a Data Adapter (Step 3)
Define the SQL statement
Select columns
Sort columns
SELECT statement
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19. Creating a Data Adapter (Step 4)
Completed SQL SELECT statement
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20. The Role of the DataSet
The DataAdapter retrieves rows into another object called a DataSet
DataSet is NOT connected to the database once the data has been retrieved
DataSet contains one or more tables
Each table in the DataSet contains one or more rows
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21. The Role of the DataSet database DataSet Your solution
DataAdapter sends command
Connection
Provider
database
DataAdapter creates DataSet
DataSet
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22. Creating a DataSet
Enter DataSet name
Select table
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23. The DataSet Class
The Tables property gets a list of tables stored in the DataSet
For each table VB .NET defines a property having the same name as the underlying table
Clear method removes all the data from the DataSet
DataSet is not connected so data is not removed from the database
AcceptChanges marks any changed rows as unchanged
Use to synchronize the DataSet with the database
GetChanges method gets rows containing changed records
HasChanges method determines if there are changed records
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24. The DataTable Class Columns property returns a collection of columns
DataSet property returns a reference to the parent DataSet object
Rows property returns the collection of rows in the DataTable
TableName property contains a string defining the table name
AcceptChanges, Clear, and NewRow methods are the same as the properties of the DataSet itself
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25. Filling a Dataset
Call the Fill method of the DataAdapter using the DataSet name as the argument
Assume that the DataAdapter is named odbdaEmployees and the DataSet is named DsEmployees1
Note pintRecords contains the number of records returned
Dim pintRecords As Integer
pintRecords = odbdaEmployees.Fill(DsEmployees1)
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26. DataBinding
Users typically want to see data appearing in a text box or other control instance
The process of associating a control instance like a text box with a field in a data source is called data binding
Two types of data binding
Simple binding – Display 1 row from a data source
Complex binding – Display multiple rows from a data source
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27. The Binding Object
Create a Binding object so as to bind a control instance to a data source
Note that the Binding object specifies the control property to bind, not the control instance to bind
Syntax:
Binding constructor
Public Sub New( ByVal propertyname As string, ByVal datasource As Object, ByVal datamember As String) As String
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28. Binding Constructor (Arguments)
propertyname contains the name of the control property to bind
The Text property of a TextBox for example
datasource contains the name of a DataSet or DataTable object
datamember provides the navigation path to a field in the DataSet
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29. Binding Constructor (Example)
Create a new binding
Text property
DataSet named DsEmployees1
Navigation Path is "tblEmployees.fldEmployeeID"
Dim pbndTemp As Binding
pbndTemp = New Binding("Text, _
DsEmployees1, _
"tblEmployees.fldEmployeeID")
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30. The ControlBindingsCollection
Using with an instance of the Binding class to bind a control
Call the Add method to bind the control instance
Call the Clear method to remove all the bindings
Count property gets the number of elements in the collection
Item property gets a specific binding from the collection
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31. Adding a Control Binding
Add method syntax:
Overloads Public Function Add ( ByVal binding As Binding ) As Binding
Binding argument contains the name of an existing binding
Method returns the binding that was added
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32. Adding a Control Binding (Example)
Create a binding and add associate it with the text box named txtEmployeeID
Dim pbndTemp As Binding
pbndTemp = New Binding("Text", DsEmployees1, _
"tblEmployees.fldEmployeeID")
txtEmployeeID.DataBindings.Add(pbndTemp)
txtEmployeeID.DataBindings.Add("Text", DsEmployees1, _
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33. Record Navigation Users need a way to navigate from record to record
Use the BindingContext of the Form class
Multiple BindingContexts can exists
CurrencyManager and BindingContext keep control instances synchronized
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34. BindingManageBase Use with the BindingContext
Set the Position property to navigate
Count property gets the number of managed rows
AddNew method adds a new item
EndCurrentEdit method ends the editing process
RemoveAt method removes a row
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35. Record Navigation (First Record)
Set the Position property of the Binding Context to 0 to locate the first row
Note Position property is 0-based
Me keyword references the form
Me.BindingContext(DsEmployees1, _
"tblEmployees").Position = 0
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36. Record Navigation (Previous Record)
Decrement the Position property of the BindingContext by 1 to locate the previous record
Me.BindingContext(DsEmployees1,
"tblEmployees").Position -= 1
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37. Record Navigation (Next Record)
Increment the Position property of the BindingContext by 1 to locate the next record
Me.BindingContext(DsEmployees1,
"tblEmployees").Position += 1
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38. Record Navigation (Last Record)
Use the underlying DataSet and DataTable to determine the row count
Me.BindingContext(DsEmployees1, _
"tblEmployees").Position = _ Me.DsEmployees1.tblEmployees.Rows.Count - 1
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39. Adding Records
When adding a record, the new record (stored in the DataSet) must be saved to the database
First get the newly added row from the database
Using the DataAdapter, call the Update method to save the changes to the database
Call the AcceptChanges method on the DataSet to synchronize the DataSet and database
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40. Adding Records (Example)
End editing, update the database, and then call AcceptChanges
Me.BindingContext(DsEmployees1, _
"tblEmployees").EndCurrentEdit
pdsInsertedRows = _
DsEmployees1.GetChanges(DataRowState.Added)
If Not pdsInsertedRows Is Nothing Then
odbdaEmployees.Update(pdsInsertedRows)
End If
DsEmployees1.AcceptChanges
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41. Deleting Records Call the RemoveAt method of the BindingContext
Call the GetChanges method on the DataSet to get the removed record
Call the Update method on the DataAdapter to save the changes
Call the AcceptChanges method on the DataSet to synchronize the DataSet and database
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42. Deleting Records (Example)
Dim pdsDeletedRows As DataSet
Me.BindingContext(DsEmployees1, "tblEmployees"). _
RemoveAt(Me.BindingContext(DsEmployees1, _
"tblEmployees").Position)
pdsDeletedRows = _
DsEmployees1.GetChanges(DataRowState.Deleted)
odbdaEmployees.Update(pdsDeletedRows)
DsEmployees1.AcceptChanges()
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43. Canceling an Update
Call the CancelCurrentEdit method on the BindingContext
Me.BindingContext(DsEmployees1, _
"tblEmployees").CancelCurrentEdit
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