Transcript ActiveX Data Control

ActiveX Data Object
ISYS 562
ADO
• An ActiveX control
ActiveX is build upon COM, a contract that
defines a standard interface by which objects
communicate.
• ADO works with several different DBMSs.
– Can use ODBC DSN.
A Client/Server Access Application
Request
Access Application
Database Server
Response
Using ODBC
• Windows 2000/2003:
• Control Panel /Administrative
Tools/DataSource(ODBC)
• Three types of data source names
– System DSN
Using ADO
• Must reference ADO objects. In VBE:
– Tools/Reference/
• click Microsoft ActiveX Data Object library 2.7
ADO Object Model
• There are three main objects on which the
ADO object models is built:
– Connection object: make connection to the
database.
– Command object: run SQL against the
database.
– Recordset object: holds some or all of the
records in database.
ADO Programming Object
Model
Connection
Errors
Error
Command
Parameters
Parameter
RecordSet
Fields
Field
Connection with a Connection
Object
• A connection object represents a unique
session with a data source.
• Connection string: database, OLE DB
provider, password, if any, security, etc.
• Use the Open method to open a connection.
• Use the Execute method to execute SQL.
• Manage transaction: BeginTrans,
CommitTrans, rollBackTrans.
Providers
• MSDASQL
– Microsoft OLE DB Provider for ODBC
• Microsoft.Jet.OLEDB.4.0
• MSDAORA – For Oracle
• SQLOLEDB – Microsoft SQL Server
Connecting String
• Containing information about database,
OLE DB provider, password, if any,
security, etc.
• For Jet database:
– Dim cn As ADODB.Connection
– Set cn = New ADODB.Connection
– cn.Open ("provider=microsoft.jet.oledb.4.0;data
source=c:\salesDB.mdb;")
ODBC DSN Connection
• When using the ODBC provider, the
connection string can be a DSN. For
example:
– Dim Cn as ADODB.Connection
– Set Cn = New ADODB.Connection
– cn.Open ("provider=msdasql;dsn=mySalesDB")
Connection Object Methods
• OPEN
cn.Open ("provider=microsoft.jet.oledb.4.0;data
source=c:\salesDB.mdb;")
Close
• Execute:
– Return a recordset after executing a SQL Select
statement.
– Usually is used to execute SQL Insert and Delete that
don’t return set of records.
• Demo
Command Objects Properties &
Methods
• Command object properties:
– ActiveConnection: Current connection
– CommandType: adCmdText, adCmdTable,
adCmdStoredProc, etc.
– CommandText: Table name if command type is
adCmdTable, SQL statement if command type
is adCmdText.
• Command object methods:
– Execute
Creating ADO Recordset Objects
• Connection object’s Execute method
• Command object’s Execute method
• Recordset’s Open method
Types of Recordset
Creating Recordset Using Connection
ForwardOnly
Option Explicit
Dim cn As ADODB.Connection
Dim rs As ADODB.Recordset
Private Sub Form_Load()
Set cn = New ADODB.Connection
cn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.mdb;")
Set rs = cn.Execute("select * from customer", adCmdText)
Creating Recordset Using Command
ForwardOnly
Option Explicit
Dim cn As ADODB.Connection
Dim rs As ADODB.Recordset
Dim cm As ADODB.Command
Private Sub Form_Load()
Set cn = New ADODB.Connection
cn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.MDB;")
Set cm = New ADODB.Command
cm.CommandType = adCmdText
cm.CommandText = "select * from customer“
Set cm.ActiveConnection = cn
Set rs = cm.Execute
Text1 = rs.Fields(0)
Text2 = rs.Fields(1)
End Sub
Creating Recordset Using Recordset’s
Open Method
(Can open any type of recordset)
Dim cn As ADODB.Connection
Set cn = New ADODB.Connection
cn.Open ("provider=msdasql;dsn=mySalesDB")
Dim rs As ADODB.Recordset
Set rs = New ADODB.Recordset
rs.Open "customer", cn, adOpenKeyset ‘Table or SQL
Dim rc As Integer
Do While Not rs.EOF
rc = rc + 1
rs.MoveNext
Loop
MsgBox (rc)
Recordset Properties
•
•
•
•
•
•
•
•
•
BOF, EOF
BookMark
CursorLocation
CursorType
LockType
MarshalOption
MaxRecords
RecordCount
Sort
Recordset Methods
• AddNew, Update, Delete
• Find: Search a recordset.
• MoveFirst, MoveLast, MoveNext,
MovePrevious
• Requery: Re-Execute the query.
• GetRows: Fetch records to an array.
Recordset Events
•
•
•
•
FetchProgress, FetchComplete
WillChangeField, FieldChangeComplete
WillMove, MoveComplete
WillChangeRecord,
RecordChangeComplete
• WillChangeRecordset,
RecordsetChangeComplete
• EndOfRecordSet
Using SQL with ADO
• SQL Select commands:
– Connection object’s Execute method
– Command object’s Execute method
– RecordSet object’s Open
• SQL Update commands: Insert, Delete, Update
– Connection object’s Execute method
• Cn.Execute “Update EmpFile Set Salary = Salary*1.05”
– Command object’s Execute method
sqlSTr = " Update EmpFile Set Salary = Salary*1.05”
cm.CommandType = adCmdText
cm.CommandText = sqlSTr
cm.ActiveConnection = cn
cm.Execute
Private Sub Form_Load()
Dim cn As ADODB.Connection
Set cn = New ADODB.Connection
cn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.mdb;")
'cn.Open ("provider=msdasql;dsn=mySalesDB")
Dim rs As ADODB.Recordset
Set rs = New ADODB.Recordset
rs.Open "select cid from customer", cn, adOpenKeyset
Do While Not rs.EOF
List0.AddItem (rs.Fields("cid"))
rs.MoveNext
Loop
End Sub
Private Sub List0_Click()
Dim cn As ADODB.Connection
Set cn = New ADODB.Connection
cn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.mdb;")
'cn.Open ("provider=msdasql;dsn=mySalesDB")
Dim rs As ADODB.Recordset
Set rs = New ADODB.Recordset
rs.Open "select cname from customer where cid = '" & List0 & "'", cn, adOpenKeyset
MsgBox (rs.Fields(0))
•
•
•
•
•
•
•
•
•
Dim rating As String
If Frame13 = 1 Then
rating = "A"
ElseIf Frame13 = 2 Then
rating = "B"
Else
rating = "C"
End If
db.Execute ("update customer set rating='" & rating & "'
where cid='" & List0 & "'")
• Text9 = rating
Recordset’s AddNew
– A form with unbound textboxes is initialized
for input.
– After entering data, a Save/Add button is
clicked and the event handler uses a pair of
AddNew and Update methods to insert record.
• Note: We can also use SQL Insert
Unbound Control Input Example
Private Sub Command8_Click()
Dim cn As ADODB.Connection
Set cn = New ADODB.Connection
cn.Open ("provider=microsoft.jet.oledb.4.0;data
source=c:\salesDB.mdb;")
'cn.Open ("provider=msdasql;dsn=mySalesDB")
Dim rs As ADODB.Recordset
Set rs = New ADODB.Recordset
rs.Open "customer", cn, adOpenDynamic, adLockOptimistic
With rs
.AddNew
.Fields("cid") = Text0
.Fields("cname") = Text2
.Fields("city") = Text4
.Fields("rating") = Text6
.Update
End With
End Sub
Find Method
• Syntax: adoRecordsetName.Find criteria
• Only accept simple comparison criteria.
• Example:
– recordset.Find “CID = ‘” & txtCID & “’”
• Finding employees hired between 2/15/2000 and 5/15/2000:
– Adodc1.recordset.Find “Hdate > #2/15/2000#”
Then use IF statement in program to filter out those hired after 5/15/2000
Note: Search starts from the current position. To search from the
beginning, must do: MoveFirst
If no match is found, the EOF of the recordset will be set to True.
Note: The search starts from the current position of the recordset. To
start from the beginning, use the MoveFirst method.
Find Code Example
Dim searchID As String
searchID = InputBox("enter searchID:")
rs.MoveFirst
rs.Find "cid='" & searchID & "'"
If Not rs.EOF Then
Text0 = rs.Fields("cid")
Text2 = rs.Fields(1)
Else
MsgBox ("not found")
End If
Demo
Using the BookMark
• Bookmark is a variant type property that
keeps the current recordset’s position. This
position can be saved in a variant variable
and later go to that position.
BookMark Example
To save bookmark:
Dim BkMark As Variant
Private Sub Command5_Click()
BkMark = rs.Bookmark
End Sub
To go to the saved bookmark location:
Private Sub Command6_Click()
rs.Bookmark = BkMark
Text0 = rs.Fields("cid")
Text2 = rs.Fields("cname")
End Sub