Transcript Visual Basic Database Access

VB .NET Database Access
ISYS546
Microsoft Universal Data Access
• ODBC: Open Database Connectivity
– A driver manager
– Used for relational databases
• OLE DB: The OLE database protocol
– Allows a program to access information in many types
of data source.
– Data provider: databases, spreadsheets, etc.
• ADO.NET: ActiveX Data Objects
– An Interface for OLE DB.
– Allow programmers to use a standard set of objects to
refer to any OLE DB data source.
.Net Applications
ADO.Net
SQL Server
OLE DB
.Net Data Provider .Net Data Provider
SQL Server
Data Source
OLE DB
Provider
OLE DB
Provider
ODBC
OLE DB
Data Source
ODBC
Data Source
Using ODBC
• Windows 2000/2003:
• Control Panel /Administrative Tools/DataSource(ODBC)
• Three types of data source names
– User DSN: usable only by you and only on the machine
currently using.
– System DSN: Any one using the machine can use.
– File DSN: Can be copied and used by other computers
with the same driver installed.
VB.NET Database Tools
• Database connection:
– Tool/Connect to database
• Provider:MS Jet 4.0 OLE DB Provider
• Connection
• Server Explorer
– Data connections:
• Right click and Add Connection
• Tables, Views
• Toolbox:Data tab
• Data Form Wizard
Steps to Retrieve Data
• Establishes a connection to the database.
• Executes commands against the database.
• Store data results.
ADO.NET Objects
.NET Applications
Data Set
Adapter Data Reader
Command Object
Connection Object
Database
ADO.NET Objects
• Connection Object: Represent a connection to the
database.
• Command Object: The command object allows us
to execute a SQL statement or a stored procedure.
• DataReader: It is a read-only and forward-only
pointer into a table to retrieve records.
• DataSet Object: A DataSet object can hold several
tables and relationships between tables.
• DataAdapter: This the object used to pass data
between the database and the dataset.
How to create an ADO.Net object?
• Using Wizard
– Data Form Wizard
– Data Adapter Wizard
• Using code:
– Example:
– dim strConn as string ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source =
c:\sales2k.mdb"
– dim objConn as new OledbConnection(strConn)
– objConn.open()
Data Form Wizard
• Creating a form with ADO.Net objects and databound controls to display and update information
in a dataset.
• Demo: Using Data Form Wizard to create a
navigational form.
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–
–
–
Project/Add Windows Form/Data Form Wizard
Set connection
Choose tables
Display records in grid or in text boxes.
Adapter & Dataset Context Menu
• Adapter:
– Properties:
• Command objects
– Configure Adapter
– Generate dataset
– Preview data
• Dataset:
– View Schema: Dataset/XML
Other Data Form Demos
• Display records in text boxes.
• Add /Modify/Delete records.
• Hierarchical forms:
– Parent/Child relationship
Creating A Database Application
Without Programming
• Creating a database application to display
information and update database.
• A main form with buttons to open data
forms:
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–
DisplayInfo
Enter New
Modify
Exit
Data Adapter Wizard
• Configure Data Adapter and generating a
dataset:
– Drag OledbDataAdapter (or database’s table) to
the form.
– Use the Data Adapter Wizard to configure the
Adapter.
– Right Click the Adapter to preview data and
creating dataset.
• Bind the dataset to controls.
Data Binding
• Connect a control or property to one or more data
elements.
• Simple binding: Use simple binding to display a
field value in controls that show Data Bindings in
the property window, such as text box or label.
• Complex binding: Use complex binding to bind
more than one field to controls such as DataGrid
and list box. Use the control’s Data Source and
Data Member to bind the data.
Creating Bound Controls
• DataGrid control:
– Data Source property
– Data Member property
– In the Form Load event, use Adapter’s Fill
method to load the dataset:
• OleDbDataAdapter1.Fill(DataSet11)
Binding Text Box
• Data Bindings property:
– Text: choose field
• Add navigation buttons:
– The current record position within the dataset is
stored in a form’s BindingContext’s Position
property. This position is zero based. Add one
move to the next record, minus one move to the
previous record.
MoveNext and MoveLast Example
• MoveNext:
–
Me.BindingContext(DataSet21, "customer").Position += 1
• MoveLast:
– Me.BindingContext(DataSet21, "customer").Position =
Me.BindingContext(DataSet21, "customer").Count -1
• How to MovePrevious and MoveFirst?
• Note: The Position property takes care of the end of file
automatically.
CurrencyManager
• Dim custCurrMgr As CurrencyManager
• Dim ordCurrMgr As CurrencyManager
• In a procedure:
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–
–
–
ordCurrMgr = Me.BindingContext(Ds31, "orders")
custCurrMgr = Me.BindingContext(Ds31, “customer")
custCurrMgr.Position += 1
ordCurrMgr.Position += 1
Binding DataGrid
• From Server Explorer, drag the table from a
database connection (or from Data tab, drag
a oleDbAdapter) onto the form.
• Create dataset.
• Drag DataGrid and set the DataSource and
Data Member property.
• Use adapter’s Fill method to load the
dataset.
Displaying Many Tables with
One DataGrid
• Define one Adapter for each table.
• Create the dataset with multiple tables.
• Add a DataGrid control and set the
DataSource proeprty to the dataset name
and leave the DataMember property blank.
Creating Hierarchical Data Grid
• Define two Adapters, one for the parent table and
one for the child table.
• Create the dataset.
• Right-click the dataset to View Schema
• Right-click the parent table and choose Add/New
Relation
• Add a DataGrid control and set the DataSource
proeprty to the dataset.parentTable and leave the
DataMember property blank.
• Note: DO File/SaveAll after creating the relation.
Binding ListBox
• Example: Bind Customer Table’s CID field to a
listbox.
– Create a Adapter to retrieve CID (and Cname) fields ,
and generate the dataset.
– Add ListBox and set binding properties:
• Data Source
• Display Member
• Value Member: the actual values for items in the list box. To
display the selected item’s value in a text box, do:
– Textbox1.text = ListBox1.SelectedValue
• Can we use TextBox1.text=ListBox1.SelectedItem?
No!
Display Selected Record
• Bound textbox:
– Me.BindingContext(DataSet11,
"customer").Position = ListBox1.SelectedIndex
–
• Unbound textbox
ListBox SelectedItem Property
• How to display the selected record in unbound
textbox?
• After binding to a data source, this property return a
DataRowView object.
• What is DataRowView?
– Object Browser:
• System.Data
– System.Data
» DataRowView:
Item property
• To retrieve a column from a DataRowView object
(use 0-based index to identity a column):
• ListBox1.SelectedItem.Item(1)
• Or: ListBox1.SelectedItem(1)
• Or: ListBox1.SelectedItem(“Cname”)
Using Object Browser
• View/Object Browser
• DataSet object model:
• System.Data
– DataSet
• Relations
• Tables
– Rows
– Columns
• Use Object Browser to study object’s properties,
methods.
Collection Structure
• Properties:
– Count
– Item(index), 0-based index
• Methods:
– Clear, Add, Insert, Remove, etc.
Navigate and Display Records in
Unbound Text Boxes
• Use code to assign field value to the text
box’s text property.
• Example:
– Dim drFound As DataRow
– drFound = DataSet11.CUSTOMER.Rows(0)
• Or DataSet11.Tables(“CUSTOMER”).Rows(0)
– TextBox4.Text = drFound.Item("cname")
• Or drFound.Item(1)
– Or: TextBox4.Text =
DataSet11.CUSTOMER.Rows(0).Item(1)
– Or: DataSet21.Tables.Item("customer").Rows.Item(0).Item(1)
Implement MoveNext Button
with Unbound Control
If rowIndex < DataSet11.CUSTOMER.Rows.Count-1 Then
rowIndex += 1
TextBox1.Text = DataSet11.Tables("customer").Rows(rowIndex).Item(0)
TextBox2.Text = DataSet11.CUSTOMER.Rows(rowIndex).Item(1)
Else
MsgBox("out of bound")
End If
Note: MovePrevious, MoveLast, MoveFirst?
Using Object Browser to Study OleDB
Object
• System.Data
– System.Data.OleDB
• OleDBConnection
– Methods: New(), New(ConnectionString), Open(), Close()
– Properties: ConnectionString, DataBase, Provider, TimeOut
• OleDBCommannd
– Methods: ExecuteReader, ExecuteNonQuery
– Properties: Connection, CommandType, CommandText,
Parameters
• OleDBDataAdapter
– Methods: Fill
– Properties: SelectCommand, InsertCommand, DeleteCommand,
UpdateCommand.
Searching with the Find Method
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•
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Another Way to Bind Listbox and Display
Selected Record
Create an adapter to retrieve Customer
records and create a dataset.
Bind the CID field to the listbox.
Use the Find method of Table’s Rows
collection to find the record.
Display the found record in unbound text
boxes.
Code Example
Private Sub ListBox1_SelectedIndexChanged(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
ListBox1.SelectedIndexChanged
Dim drFound As DataRow
drFound = DataSet41.CUSTOMER.Rows.Find(ListBox1.SelectedValue)
‘ Assume SelectedValue is CID
TextBox1.Text = drFound.Item("cname")
TextBox2.Text = drFound.Item("rating")
End Sub
Note: We can get the search value from other controls such as InputBox
and Textbox.
How to Determine If Record Exists
or Not
Dim foundRow As DataRow
Dim SearchValue as String
SearchValue=InputBox(“Enter CID”)
foundRow = DataSet41.CUSTOMER.Rows.Find (SearchValue)
If Not (foundRow Is Nothing) Then
TextBox1.Text = drFound.Item("cname")
TextBox2.Text = drFound.Item("rating")
Else
Messagerbox.show(“Record not exist”)
End If
Creating Parameter Query with Adapter
Configuration Wizard
• Parameter query: Selection criteria is entered at
run time.
• Command object’s Parameters property.
• Example: Orders table: OID, CID, Odate,
SalesPerson
• To create a parameter for the CID field:
– In the Query Design window’s criteria column of the CID field, add
criteria: =?
• To assign the parameter value:
– OleDbDataAdapter2.SelectCommand.Parameters("cid").Value =
• Demo: Get CID from a InputBox and display orders.
Parameter Query Example:
• Select CID from a listBox and display
orders of the selected CID in a DataGrid
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–
–
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Create and bind the listbox (specify the valueMember).
Create a second adapter and define a parameter query.
In the Query Design window’s criteria column, add criteria: =?
Generate a 2nd dataset (DataSet21 in this example) with the
parameter.
– Create and bind the DataGrid to the dataset.
– In the listbox’s SelectedIndexChanged event, assign the selected
value to the parameter and fill the dataset:
• DataSet21.Clear()
• OleDbDataAdapter2.SelectCommand.Parameters("cid").Value =
ListBox1.SelectedValue
• OleDbDataAdapter2.Fill(DataSet21)
Display Selected Record in Text Boxes
with Parameter Query
• Create and bind the listbox.
• Create a second adapter and define a parameter query.
– In the Query Design window’s criteria column, add criteria: =?
• Generate the dataset with the parameter.
• Create and bind textboxes to the dataset.
• In the listbox’s click event, assign the selected value to the
parameter and fill the dataset:
– DataSet11.Clear()
– OleDbDataAdapter2.SelectCommand.Parameters("cid").Value =
ListBox1.SelectedValue
– OleDbDataAdapter2.Fill(DataSet11)
Send Changes in a Bound DataGrid
Back to the Database
• Updating records in DataGrid:
– New records are added at the end of the grid.
– To delete a record, click the leftmost column to select
the record, then press the delete key.
– Modify record
• Add an Update button that use adapter’s update
method to send changes back to the data source:
– OledbDataAdapter1.Update(Dataset11)
Creating Parent/Child Form with
Binding
• Dataset contains Customer and Orders with
relation CustomerOrders.
• Bind the textboxes to Customer table.
• Bind the datagrid to the relation:
– DataSource: Dataset
– DataMember: Customer/CustomerOrders
• Note: Study the form created by the Data Form
Wizard.