Joost van der Sluis wrote:
On Tue, 2010-11-23 at 16:01 +0000, Mark Morgan Lloyd wrote:
Before anything else I'd like to say that I'm entirely familiar with
transactions in the SQL context. However I've been having a bit of
difficulty sorting out the relationship between a TPQConnection,
multiple TSQLQuery, and transaction object(s).
Since this is strictly read-only, I can't see why I need transactions,
but I obviously respect the judgment of whoever designed the architecture.
Well, you always need a transaction. Without a transaction, Postgres
will do nothing, ever.
I assume you are used to the fact that postgres automatically creates an
transaction for you. With Sqldb you have to do this yourself.
Just got there- I'd forgotten that one :-)
Am I correct in my understanding that in order to close the transaction
I have to set Action (e.g. to caRollback) and then Active to False? It
appears that if I don't do this the query never sees data being updated
at the backend.
To close the transaction, use .commit or .rollback. (In your
case .rollback)
That the query isn't updated, isn't that because it's cached? Did you
close and reopened the query?
Yes, I was always seeing the same data until I started forcibly closing
the transaction. When I queried server statistics I could see that the
same transaction had been active for an extended period, and when
running manual tests (using the psql utility) I determined that that was
the way that PostgreSQL behaved.
If that does not help, you have to set the proper
transaction-properties, so that it can read data committed in other
transactions.
To support the two TSQLQuery objects, do I need one or two
TSQLTransaction objects? If I have to have two TSQLTransaction objects,
does that imply that I also have to have two TPQConnection objects?
Just one.
Thanks, working on it.
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
--
_______________________________________________
Lazarus mailing list
[email protected]
http://lists.lazarus.freepascal.org/mailman/listinfo/lazarus
