"Frank Millman" wrote in message news:mqcslv$tee$1...@ger.gmane.org...
"Frank Millman" wrote in message news:mqcmie$po9$1...@ger.gmane.org...
> Hi all
>
> I have a 'data integrity' problem with sqlite3 that I have been battling
> with for a while. I have not got to the bottom of it yet but I do have
> some useful info, so I thought I would post it here in the hope that
> someone with some knowledge of the internals of the python sqlite3
> module can throw some light on it.
Oops, I have just spotted my mistake.
There are times when I want to issue a SELECT statement with a lock, as it
will be followed by an UPDATE and I do not want anything to change in
between.
MS SQL Server allows you to add 'WITH (UPDLOCK)' to a SELECT statement,
PostgreSQL allows you to add 'FOR UPDATE'.
I could not find an equivalent for sqlite3, but in my wisdom (this was
some time ago) I decided that issuing a 'BEGIN IMMEDIATE' would do the
trick.
I had not anticipated that this would generate an implied COMMIT first,
but it makes sense, and this is what has bitten me. Now I must try to
figure out a better solution.
For the record, I have figured out a better solution.
I was on the right lines with 'BEGIN IMMEDIATE', but I had overlooked the
possibility that there could be a transaction already in progress.
Now I have changed it to -
if not conn.in_transaction:
cur.execute('BEGIN IMMEDIATE')
So far it seems to be working as intended.
Frank
P.S. Many thanks to the maintainers of the sqlite3 module for continuing to
enhance it. 'in_transaction' was added in 3.2, and 'set_trace_callback' was
added in 3.3. Without these my life would have been much more difficult.
--
https://mail.python.org/mailman/listinfo/python-list
