Classic ASP VBScript need dropin replacement for MyConn.Execute( query ) - mysql

Question

I have a site running on ASP VBScript, and the original code never closes a DB connection. It opens connections as part of "startup" for any given page, then does whatever it does and stops -- but never explicitly closes connections. This is now causing problems where things are crashing at the web server level -- presumably from the lack of garbage collection.
So I want to make a function that acts as a drop-in replacement for all the MyConn.Execute( sqlQuery ) commands throughout the site. I've found some good candidates, but none of them seem to quite work. The most promising appears to be the code below, but when I try to actually use the recordset returned I get an error.
Function GetRS(strSQL)
'this function returns a disconnected RS
'Set some constants
Const adOpenStatic = 3
Const adUseClient = 3
Const adLockBatchOptimistic = 4
'Declare our variables
Dim oConn
Dim strSQL
Dim oRS
'Open a connection
Set oConn = Server.CreateObject("ADODB.Connection")
oConn.ConnectionString = "Driver={MySQL ODBC 5.3 Unicode Driver};Server=localhost;User=foo;Password=bar;Database=baz"
oConn.Open
'Create the Recordset object
Set oRS = Server.CreateObject("ADODB.Recordset")
oRS.CursorLocation = adUseClient
'Populate the Recordset object with a SQL query
oRS.Open strSQL, oConn, adOpenStatic, adLockBatchOptimistic
'Disconnect the Recordset
Set oRS.ActiveConnection = Nothing
'Return the Recordset
Set GetRS = oRS
'Clean up...
oConn.Close
oRS.Close
Set oConn = Nothing
Set oRS = Nothing
End Function
'call the function
strSQL = "SELECT * FROM Authors"
set RS = GetRS(strSQL)
(source: https://web.archive.org/web/20211020134116/https://www.4guysfromrolla.com/webtech/080101-1.shtml)
Here's my test code:
Set rs = GetRS( "SELECT `first_name` FROM `users` WHERE `id`=123" )
x = rs( "first_name" )
response.write x
I get the error:
ADODB.Recordset error '800a0cc1'
Item cannot be found in the collection corresponding to the requested name or ordinal.
/test.asp, line 25
Using an ordinal -- rs(0) -- returns the same error.
Looks like an empty recordset to me, but it's a legit Query that does return a record.
Does anyone know why this isn't working, or can point me to other code that will do the job? (Especially with practical usage examples, which the 4guys article lacks.)

Answer 1

My understanding is that a a Recordset is tied to the datasource. When you execute a query, by default, the client (your program) doesn't get the entire contents of the query, but will wait until you actually request the data. That way, you can choose a specific page size, page offset etc. to efficiently select rows from the database without transferring potentially millions of rows over the wire.
As a side-effect of this, if you close the database connection, you will no longer be able to use the Recordset. You must leave the connection open until you are done with it. In the same way, closing the Recordset itself will stop you from being able to interact with it further.
You have two options: copy the data out of the Recordset into your own variables/arrays before closing, or use a different technique to manage your connection. I'll talk about the latter option here.
There is technique which will allow you to open the DB connection once, and ensure it is closed properly by VBScript when it terminates.
Class DbConnectionManager
Private Sub Class_Initialize()
Set oConn = Server.CreateObject("ADODB.Connection")
oConn.ConnectionString = "Driver={MySQL ODBC 5.3 Unicode Driver};Server=localhost;User=foo;Password=bar;Database=baz"
oConn.Open
End Sub
Private Sub Class_Terminate()
oConn.Close
End Sub
End Class
Dim connMgr : Set connMgr = New DbConnectionManager
This code snippet is untested, but the general principle is that you start your program by defining a class and creating an instance of it. When a class instance is created, Class_Initialize is called, and when your program ends (or the instance gets removed and garbage-collected), then Class_Terminate will be called. That means oConn.Close should always be called before your program ends, even in the event of an error.
This is a very basic example of how classes work, but you could actually extend the class further and insert your Execute functions into the class itself to encapsulate the database connection details for easier maintenance. If you haven't used classes in VBScript yet but you have a basic understanding of how Object-Oriented programming works, I would highly recommend you try that.
Bonus extra: It looks like you're passing in raw SQL strings. To avoid SQL injection vulnerabilities, don't build your SQL queries dynamically. Instead, use ADO and parameters so any user-created content can be safely passed into the query without security risks. How do I run a parameterized SQL query in classic ASP? And is it secure? W3Schools also has a section on how to use ADO.