Matakuliah : M0492 / Web-based Programming Lanjut
Tahun
: 2007
Web-based Programming Lanjut
Pertemuan 5
ActiveX Data Object (ADO)
• OLE DB and ADO Architecture
• The ADO Object Model
– Connection Object
– Command Object
– Recordset Object
– Record Object
– Stream Object
– Collections
• Connecting to Data Stores
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ADO Basics
• ActiveX Data Object (ADO)
– The components that allow us to interact with data stores
– One way to access data
• OLE DB
– The underlying technology
– Interfaces between our programs and the source of the data
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OLE DB and ADO Architecture
Application
VC++
VB
Script
Java
ADO
OLEDB
RDBMS
E-mail
Data Store
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Directory
Services
OLE DB and ADO Architecture
• ADO is a COM component and can be used in any COM compliant language, such as
Delphi, or scripting language that supports the Active Scripting interface.
• OLE DB was not designed to be used in all language, so ADO sits on top of OLEDB,
and provides an interface for those languages, such as VB and scripting
languages, which can’t access OLE DB directly.
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OLE DB and ADO Architecture
• Two main reasons why do we need OLEDB and ADO
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First, OLEDB and ADO are designed to give you access to data stores. Note that ‘data
store’ does not always be ‘databases’. Although databases are still the most widely
used form of data storage, they don’t necessarily contain all of your data.
Second, the rise of Internet applications, and the stateless nature of the Web. The
older data access methods aren’t designed to handle data when they are not
permanently connected to their store of data. OLEDB and ADO provide disconnected
recordsets.
The ADO Object Model
Errors
Collection
Connection
Active
Connection
Command
Execute()
ActiveCommand
Active
Connection
ActiveConnection
Recordset
SourceRecordset
GetChildren()
Execute()
Open()
Collection
Collection
Collection
Fields
Save()
Open()
Open()
Parameters
Stream
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Record
Source
The ADO Object Model
• The Connection Object
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The Connection object is what enables us to connect to data stores. Can be
constructed or stored commands (for example SQL command or a stored procedure)
We can specify which OLEDB Provider we wish to use, the security details used to
connect to the data store, and any other details.
It is not necessary to explicitly create a Connection object to connect to a data store.
We can create Command, Recordset and Record objects without a Connection object
ADO implicitly creates a Connection object if we do not create one ourself.
The ADO Object Model
• The Command Object
– The Command object is designed for running commands against a data store.
– Connection objects has restrictions on its facilities for handling commands,
whereas the Command object was specifically created for dealing with all
aspects of commands.
– Implicitly created when we run a command from the Connection object.
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The ADO Object Model
• The Recordset Object
– Probably is the most commonly used object in ADO, since it is this object that
contains the sets of data we extract from our data stores.
– The Recordset is the object that holds set of records.
– It allows us to change the data (additions, updates and deletions), move
around the records, filter the records, and so on.
– Contains a Fields collection, where there is a Field object for each field
(column) in the recordset.
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The ADO Object Model
• The Record Object
– The Record object is used to model a semi-structured recordset in ADO.
– Semi-structured recordset is the sets of data where the columns may be
different (number of column and data type) for each row.
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The ADO Object Model
• The Stream Object
– The Stream object is used to access the contents of a node, such as an email
message, or a Web page.
– Have access to the actual contents of a file, or resource.
– The Stream object is designed to handle binary data.
– Another use for streams is XML, where we can access a set of data (structured
or semi-structured) as a stream of XML.
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The ADO Object Model
• Collections
– The Fields Collection
Holds Fields object associated with a recordset or a record.
– The Parameters Collection
Used solely by the Command object, and identifies the parameters in stored
commands.
– The Errors Collection
Contains details of the last ADO or OLE DB Provider error that was generated
by a command, and can be only accessed through the Connection object.
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The ADO Object Model
– The Properties Collection
Designed to work with many different data stores, each of which might have
different facilities
Connection
Properties
Record
Command
Recordset
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Fields
The ADO Object Model
• We can use the same structure of code to loop through the collections:
The syntax in VBScript is :
For Each Object In Collection
‘ Do Something with object
Next
For example, to loop through the Fields collection of a Recordset object :
For Each objField In rs.Fields
Response.Write objField.Name & “<BR>”
Next
If you prefer JScript, then you can use the Enumerator object :
for (objField = new Enumerator(rs.Fields); !objField.atEnd(); objField.moveNext())
Response.Write (objField.item().Name + ‘<BR>’);
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The ADO Object Model
Example of loop through Errors Collection :
For Each objError In rs.ActiveConnection.Errors
Response.Write objError.Name & “<BR>”
Next
Example of the OLE DB Provider for Jet allows us to access the Jet
specific security properties:
Set conDB = Server.CreateObject(“ADODB.Connection”)
conDB.Open “DSN=NWind”
conDB.Properties(“Jet OLEDB:Database Password”) = “LetMeIn”
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The ADO Object Model
•
ADO Constants
–
The first method of reference the constants is to include them in your ASP file:
<!-- #INCLUDE FILE=“adovbs.inc” -->
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You can either copy the include file into your local directory, or reference it from the
installation directory. One disadvantage of this method is that it makes your ASP page
larger, since a whole host of constants are included, many of which you won’t typically
need.
A better solution is to create a reference to the type library, which makes the constants
available without having to include them in the file :
<!– METADATA TYPE=“typelib” FILE=“C:\Program Files\Common Files\System
\ado\msado15.dll” -->
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Connecting to Data Stores
• Several different ways connect to a data source:
– A Connection String. Put the connection details in a string, or directly into the
command that opens the data store.
– A Data Link File. A file (with a .udl extension) that contains the connection
details.
– ODBC Data Source, or DSNs. Similar to Data Link files, but are only applicable
to ODBC Data Sources. To be used in an ASP page, the Data Source must be a
System Data Source.
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Connecting to Data Stores
• Connection Strings
The connection string varies upon the Provider. The OLEDB Provider for ODBC is
the default – therefore if you leave off the Provider= section, you will
automatically use ODBC.
– Microsoft Access
If using an ODBC connection, without a DSN:
Driver = {Microsoft Access Driver (*.mdb)}; DBQ=C:\MyData\thedata.mdb
For native OLE DB Provider:
Provider=Microsoft.Jet.OLEDB.4.0; Data Source= C:\MyData\thedata.mdb
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Connecting to Data Stores
– Microsoft SQL Server
Using the Provider for ODBC:
Driver = {SQL Server}; Server=server_name; Database=database_name;
UID=user_name; PWD=user_password
For example:
Driver = {SQL Server}; Server=MUGGLE; Database=pubs; UID=arine; PWD=letmein
For the native OLE DB Provider:
Provider =SQLOLEDB; Data Source=server_name; Initial Catalog=database_name;
User Id=user_name; Password=user_password
For example:
Provider =SQLOLEDB; Data Source=MUGGLE; Initial Catalog=pubs; User Id=arine;
Password=letmein
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Connecting to Data Stores
– Microsoft Indexing Service
The Indexing Service is only accessible through a native OLE DB
Provider. The syntax is:
Provider =MSIDXS; Data Source=catalog_name
For example, using the Web catalog:
Provider =MSIDXS; Data Source=Web
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Connecting to Data Stores
• ODBC Drivers
In the example that use the OLE DB for ODBC, the Driver is shown in curly braces.
For example:
Driver={Microsoft Access Driver (*.mdb)}; DBQ=C:\MyData\database_name.mdb
The name you should use be the
exact name taken from the list of
drivers when creating a new
data source :
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Connecting to Data Stores
• Data Link Files
Create a Data Link file by simply
creating a blank text file and
renaming the extension to .udl.
Once you have the physical data link
file, you can open it, either by
double-clicking, or right-mouse
clicking and selecting Open. You are
presented with the following dialog:
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Connecting to Data Stores
The details of this screen change
depending upon the Provider
selected. Note that if you select the
Allow saving password option, the
password you type will be saved in
plain text in the UDL file.
To change the Provider you can
select the Provider tab:
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Connecting to Data Stores
Alternatively, you can edit the file in a text editor :
You can select that the UDL file is really just storing a connection string. To
use the data link you simply specify the data link file when opening the
connection:
conDW.Open “File Name=C:BI\Batches.udl”
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Connecting to Data Stores
•
ODBC Data Sources
ODBC Data Sources (commonly called
Data Source Names, or DSNs) are set up
through the Data Sources option on the
Administrative Tools menu. Previous
versions of Windows had this as an applet
in the Control panel.
To access a DSN from an ASP page you
must make sure that the DSN is set up as
a System DSN.
This simply involves selecting the System
DSN tab on the Data Source
Administrator, and then selecting the
Add.. button:
Once a DSN is set up, you use the DSN= attribute of the connection string.
For example:
conDW.Open “DSN=pubs“
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Using Include Files
• Using include files to contain connection strings gives a central place to store the
connection details for a number of ASP pages.
<%
strConn = “Provider=SQLOLEDB; Data Source=MUGGLE; “ & _
“Initial Catalog=pubs; User Id=Arine; Password=letmein”
Response.Write “”
%>
Connection.asp
• In your ASP pages, add this on the top of the page:
<!-- #INCLUDE FILE=“Connection.asp” -->
This saves you having to type the connection details for each ASP page, and lets
you change the connection used for the entire site from one central location.
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Using Connection State
• Storing the connection string in an Application variable is quite a common trick
too, and equally as effective as using an include file. For example, you could add
the following to your global.asa file:
Sub Application_OnStart()
strConn = “Provider=SQLOLEDB; Data Source=MUGGLE; “ & _
“Initial Catalog=pubs; User Id=Arine; Password=letmein”
Set Application (“ConnectionString”) =strConn
End Sub
In your ASP pages you can then use the following :
Set conDW = Server.CreateObject(“ADODB.Connection”)
conDW.Open Application(“ConnectionString”)
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Connection Syntax
• If using an explicit Connection object, use the Open method:
connection.Open [ConnectionString], [UserID], [Password], [Options]
The arguments are as follows:
Argument
Description
ConnectionString
The string containing the connection details. This can be the name of an ODBC DSN, the name
of a Data Link file, or just the actual connection details.
UserID
The name of the user to use during the connection. This overrides any user name supplied in
the connection string.
Password
The password for the user. This overrides and password details supplied in the connection
string.
Options
This can be adAsyncConnect to specify that the connection be established asynchronously.
Omitting this parameter ensures a synchronous connection.
Connecting asynchronously is no use in an ASP environment, since scripting
languages can’t receive events from ADO.
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Connection Examples
•
To open a connection use the Open method of the Connection object. For example, assume that
strConn contains a valid connection string:
Set conPubs = Server.CreateObject(“ADODB.Connection”)
conPubs.Open strConn
‘ Some processing
conPubs.Close
•
Alternatively, use the ConnectionString property:
Set conPubs = Server.CreateObject(“ADODB.Connection”)
conPubs.ConnectionString = strConn
conPubs.Open
‘ Some processing
conPubs.Close
•
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There is no difference between the two, and if you use the former method, then the ConnectionString
property is filled in for you.