Using SELECT LAST() with pyodbc and MSACCESS sometimes returns same value

Question

I have a strange problem that Im having trouble both duplicating and solving.

Im using the pyodbc library in Python to access a MS Access 2007 database. The script is basically just importing a csv file into Access plus a few other tricks.

I am trying to first save a 'Gift Header' - then get the auto-incrmented id (GiftRef) that it is saved with - and use this value to save 1 or more associated 'Gift Details'.

Everything works exactly as it should - 90% of the time. The other 10% of the time Access seems to get stuck and repeatedly returns the same value for cur.execute("select last(GiftRef) from tblGiftHeader").

Once it gets stuck it returns this value for the duration of the script. It does not happen while processing a specific entry or at any specific time in the execution - it seems to happen completely at random.

Also I know that it is returning the wrong value - in other words the Gift Headers are being saved - and are being given new, unique ID's - but for whatever reason that value is not being returned correctly when called.

SQL = "insert into tblGiftHeader (PersonID, GiftDate, Initials, Total) VALUES "+ str(header_vals) + ""
cur.execute(SQL)

gift_ref = [s[0] for s in cur.execute("select last(GiftRef) from tblGiftHeader")][0]

cur.commit()

Any thoughts or insights would be appreciated.

Answer 1

In Access SQL the LAST() function does not necessarily return the most recently created AutoNumber value. (See here for details.)

What you want is to do a SELECT @@IDENTITY immediately after you commit your INSERT, like this:

import pyodbc
cnxn = pyodbc.connect('DRIVER={Microsoft Access Driver (*.mdb, *.accdb)};DBQ=C:\\Users\\Public\\Database1.accdb;')
cursor = cnxn.cursor()
cursor.execute("INSERT INTO Clients (FirstName, LastName) VALUES (?, ?)", ['Mister', 'Gumby'])
cursor.commit()
cursor.execute("SELECT @@IDENTITY AS ID")
row = cursor.fetchone()
print row.ID
cnxn.close()

Answer 2

Yep! That seems to be a much more reliable way of getting the last id. I believe my initial code was based on the example here http://www.w3schools.com/sql/sql_func_last.asp which I suppose I took out of context.

Thanks for the assist! Here is the updated version of my original code (with connection string):

MDB = 'C:\\Users\\Public\\database.mdb'
DRV = '{Microsoft Access Driver (*.mdb)}'
conn = pyodbc.connect('DRIVER={};DBQ={}'.format(DRV,MDB))
curs = conn.cursor()

SQL = "insert into tblGiftHeader (PersonID, GiftDate, Initials, Total) VALUES "+ str(header_vals) + ""
curs.execute(SQL)
curs.commit()
curs.execute("SELECT @@IDENTITY AS ID")
row = curs.fetchone()
gift_ref = row.ID