TechTip: Connect to the iSeries DB2 Database from an Active Server Page

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Using the iSeries DB2 database from an Active Server Page (ASP) can really expand your application development possibilities. The problem is that setting the whole thing up can get a bit confusing. Let me take you step by step through what you need to do to start using iSeries DB2 data from within an ASP.

For starters, you need a Web server that can serve ASPs. The good news here is that Microsoft's Internet Information Server (IIS) does this "out of the box." The next thing you need to do is install the Client Access OLE DB provider on the Web server. This can be found under the Data Access option within the Client Access setup program. Once you have ensured that the OLE DB provider is installed, you're ready to start work on the ASP.

Connecting to the iSeries DB2 database requires the use of ActiveX Data Objects (ADO). ADO accomplishes database connectivity through the use of the following three objects:

ADODB.Connection--This object defines the data source itself.
ADODB.Command--This object is used to pass commands (updates, deletes, etc.) to the database.
ADODB.Recordset--This object is used to read data from the database.

The record and field selection is done using standard SQL statements. The process of reading data from an OLE DB provider using ADO is pretty simple. First, you need to define the Connection object attributes, including the provider name, data source name, user ID, and password. You retrieve data through the use of the Recordset object as shown in the example below:

<% 
Set objConn=Server.CreateObject("ADODB.Connection")
Set objRs=Server.CreateObject("ADODB.Recordset")

objConn.Open "Provider=IBMDA400;  Data Source=S1234ABC; ","User","Secret"

objRs.Open "SELECT * FROM QSYS2.SYSTABLES",objConn
objRs.MoveFirst
response.Write objRs.Fields(0).Value
%>


When executed in the browser, this example will display a file name. In this example, you first use the Server.CreateObject command to access the Connection and Recordset ActiveX objects. Next, you use the Open method of the Connection object. The first parameter provided on this command defines the ConnectionString. This value contains the provider name, which in the case of the iSeries is IBMDA400, and the data source, which will be the name or IP address of your iSeries. The next two parameters define the user ID and password to be used to log on to your iSeries.

Once you've defined your Connection, you're ready for the Recordset. Again, you use the Open method, but this time the two parameters provided define the data source and the Connection object to be used to access that source. The data source parameter contains a simple SQL SELECT statement that defines the data you want to retrieve.

In this example, you are selecting all fields from the SYSTABLES catalog. Next, you use the MoveFirst method to move to the top of the selected Recordset. The final line shown sends the value of the first field from the recordset to the client browser, using the Fields collection. This collection can be accessed by using a numeric value to represent the position of the field in the file or by using a text string containing the field name itself, as shown below:


response.Write objRs.Fields(0).Value
'  or 
response.Write objRs.Fields("NAME").Value

The Command object is similar to the Recordset object in that it allows you to access data within your database. As the name suggests, however, this object allows you to modify the data within this database. The sample shown below could be used to delete all records from the specified table:

<% 
Set objConn=Server.CreateObject("ADODB.Connection")
Set objCmd=Server.CreateObject("ADODB.Command")

objConn.Open "Provider=IBMDA400;  Data Source=S1234ABC; ","User","Secret"

objCmd.ActiveConnection=objConn
objCmd.CommandText="DELETE  * FROM MYLIB.MYFILE"
objCmd.Execute
>% 

Define the connection object as you did in the earlier example. Then, use the ActiveConnection property to define the connection to be used for the Command. Next, define the CommandText property of the Command object. In this case, it's nothing more than an SQL DELETE statement. Finally, use the Execute method of the Command object to execute the statement. You can also use the Command object to run a command on the iSeries. The example below uses the QCMDEXC API to execute a command on the iSeries:

<% 
Set objConn=Server.CreateObject("ADODB.Connection")
Set objCmd=Server.CreateObject("ADODB.Command")

objConn.Open "Provider=IBMDA400;  Data Source=S1234ABC; ","User","Secret"

objCmd.ActiveConnection=objConn

cmd="'OVRDBF FILE(myfile) MBR(MBR002) OVRSCOPE(*JOB)'" 
Lnt=RIght("0000000000" & len(cmd)-2,10) & ".00000" ' 
objCmd.CommandText = "CALL QSYS.QCMDEXC(" & cmd & " , " & Lnt & ")"
objCmd.Execute

>% 

In this example, you are using the OVRDBF command to override the member to be used the next time the file "MYFILE" is accessed. After you create the text for the command itself, you need to determine the length of the command to pass to QCMDEXC. Then, you define the CommandText parameter containing the QCMDEXC API. Finally, you use the Execute method to run the command. This override will be active throughout the life of the connection.

As you're working with ASP, one thing that can be troublesome is error handling, since there's no real debugging environment for ASP. There's a simple workaround, though. If you disable automatic error handling within your ASP script, you can trap the errors within the script manually. The example below does just this:

<% 
On Error Resume Next

Set objConn=Server.CreateObject("ADODB.Connection")
Set objRs=Server.CreateObject("ADODB.Recordset")

objConn.Open "Provider=IBMDA400;  Data Source=S1234ABC; ","User","Secret"

objRs.Open "SELECT * FROM QSYS2.SYSTABLES",objConn

If objConn.Errors.Count>0 Then
For x=0 to objConn.Errors.Count-1
Response.Write objConn.Errors(x) & "
"

Next x
End If 

objRs.MoveFirst
response.Write objRs.Fields(0).Value
%>


This modified version of the original example first uses the ON ERROR RESUME NEXT command to disable error handling and then uses the Errors collection of the Connection object to determine if the OLE DB provider returned any errors to the application. This is an easy way to monitor for SQL syntax errors or other errors within the definition of your data source.

This basic technique can be used over and over again to let you create entire applications using ASP to connect to the iSeries DB2 Database.

--Mike Faust
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