What is correct way to set up VBA ADO connection from Excel to Access for multiple users and files? - vba

Question

I have several excel files that are used for entering data. Files are identical in functionality, one for each service center of ours. In the form there is button that launches a macro which transforms data to table format on another sheet which is then later uploaded to Access db.
Everything worked fine on my own computer. Adding new rows, updating existing rows and deleting existing roles. I had used early binding which lead to problems when I moved files to our network drive. I managed to convert files to late binding but then other problems arose.
Most of the time, uploading to Access isn't working, especially when multiple users try to do stuff at the same time. Most common error code is that I am not using updateable query or that this method doesn't support backwards scrolling. I sorry for not reporting actual error codes, but I can't replicate them at the moment.
My connection code is as follows, it is bit of a mix of copy paste code from different examples.
Opening the connection and other prestuff
Sub excel2access()
Const adUseClient = 3
Const adUseServer = 2
Const adLockOptimistic = 3
Const adOpenKeyset = 1
Const adOpenDynamic = 2
Dim oConn As Object
Dim cmd As Object
Dim rs As Object
Dim r As Long
Dim criteria As String
Dim Rng As Range
Set oConn = CreateObject("ADODB.Connection")
Set cmd = CreateObject("ADODB.Command")
oConn.Open "Provider=Microsoft.ACE.OLEDB.12.0;" & _
"Data Source= '" & Range("dbpath").Value & "\" & Range("dbfile").Value & "' ;"
Set rs = CreateObject("ADODB.Recordset")
rs.CursorLocation = adUseClient
rs.CursorType = adOpenStatic
rs.LockType = adLockOptimistic
rs.Open "Select * from need_rows WHERE service_center = '" & Range("scenter_name").Value & "'", oConn
r = 2 ' the start row in the worksheet
Sheets("data").Select
This following bit looks through data in excel sheet and tries to find match from recordset found for that service center. If match is not found new record is created and if match is found the old record is updated.
Do While Len(Range("A" & r).Formula) > 0
With rs
criteria = Range("D" & r).Value
.Find "identifier='" & criteria & "'"
If (.EOF = True) Or (.BOF = True) Then
.AddNew ' create a new record
.Fields("service_center") = Range("scenter_name").Value
.Fields("product_id") = Range("A" & r).Value
.Fields("quantity") = Range("B" & r).Value
.Fields("use_date") = Range("C" & r).Value
.Fields("identifier") = Range("D" & r).Value
.Fields("file_type") = Range("file_type").Value
.Fields("use_type") = Range("E" & r).Value
.Fields("updated_at") = Now
.Update
Else
If .Fields("quantity") <> Range("B" & r).Value Then
.Fields("quantity") = Range("B" & r).Value
.Fields("updated_at") = Now
.Update ' stores the new record
End If
End If
.MoveFirst
End With
r = r + 1
Loop
rs.Close
Set rs = Nothing
Set oConn = Nothing
MsgBox "Confirmation message"
End Sub
Edit: Based on link by barrowc I changed cursor type to adOpenStatic. I made a test with several users trying to upload data at the same time and everything worked perfectly. Until one user stayed in the file and spent quite a while editing data there and then tried to upload data to db and got following error message: https://dl.dropbox.com/u/3815482/vba_error.jpg
Again, I am back where I started from.
Also, I am open to feedback on my code in general as well.
I am using Office 2010.
Am I doing it wrong? All help is appreciated.

Answer 1

You are going to have a lot of issues with the database being locked by other users. This is for several reasons:
From what I can see you are not handling errors. Therefore if your script errors half way through the connection will be left open thus causing lock problems.
By the looks of this, the macros could potentially keep the connection open for a decent amount of time (assuming no errors).
Having created a lot of macros connecting to an MS Access database I can tell you straight up. You are going to have a lot of connection issues where the database is being locked by spreadsheets that someone has left open all day/night due to things such as not handling unexpected errors (the connection never closes).
Even once you fix the problems all you need is ONE person to be using the spreadsheet with the old code and they will continue to lock the database.
One massive problem is that if someone connects to the database when its already open by someone else I believe they inherit the connection type of the already opened database resulting in a daisy chain of write locks. You then need to make sure all connections are severed in order to reset the connection.
You have also not shown us how the data is put into the spreadsheet in the first place. Perhaps you are not correctly closing the connection and that could potentially be the reason why sometimes the database is locked.
There are many different things you could try to get around this:
Easiest would be to use MS Access Front End + MS Access Back End.
Instead of pressing this button and uploading the data through connection strings you could make it save the file in a folder which would then be processed by an ms access database that is sitting there watching the folder. This would mean that you upload script would be written in MS Access and just be processing the files. Wouldn't be as instantaneous as your current approach but all write connections would be coming from the same machine/user in this circumstance.
Persist with the current method: eventually you may get it to a stable state but it will be a lot of frustration and effort as determining the reason for a lock may not always be easy. You could at least look at who has the file locked at the time and work from there but as mentioned earlier they may not have been the cause of the lock. They may have just inherited the lock type.
Personally I like to use MS Excel to display MS Access data for users, but avoid like a plague getting it to update MS Access. However if I was to do this I would do it through the use of oConn.Execute commands not opening a recordset, comparing and slowing pushing as that would keep the connection open too long.
Sorry for the wall of text. Hope this information helps.

Answer 2

sounds to me like Jet isn't reliable enough for your environment. I frequently use SQL Server / Access Data Projects to consolidate information from multiple spreadsheets into a single database backend that doesn't barf when you add a half dozen users.

Answer 3

You could also try using action queries.
First I would try to update using (you may need to format the now value)
dim count as long
oConn.Execute "UPDATE need_rows SET quantity = " & Range("B" & r).Value & ", updated_at = #" & Now & "# WHERE service_center = '" & Range("scenter_name").Value & "' AND identifier='" & Range("D" & r).Value & "' AND quantity <> " & Range("B" & r).Value", count
If count is zero then no row was updated, so either there was no row to update or the quantity hasn't changed. Either way we can try to INSERT, which will fail in the latter case, but without causing problems.
if count = 0 then
count = oConn.Execute "INSERT ...", count
if count = 0 then
' quantity has not changed, so nothing to do
else
' new record inserted
end if
else
' record updated
end if