Hello Adam,

That´s right, after B/R transaction id are reset. The problem adding
timestamp or updatenumber field to table is that i have to add this
field in all tables and build a BI triggers for it. I´m lokking for more
general solution, that´s the reason because buffer comparison was
implemented first.

Thanks
Danny


Adam wrote:

> --- In firebird-support@ yahoogroups. com
> <mailto:firebird-support%40yahoogroups.com>, Danny Garcia Hernandez
> <danny@...> wrote:
> >
> > Hi, i have used buffer comparison to implement optimistic blocking.
> When
> > my component call post with update transaction, the component read
> > inside other transaction the same record on the table, reading this
> > record with a buffer and check it with the oldbuffer looking for
> > diferences between buffers data. If some field have changed then i show
> > a message to ask post confirmation.
> >
> > I think that buffer comparison is not the best option (what happen
> with
> > blob comparison?) , but is the only that i have right now.
> >
> > BTW, i´m looking for other solutions. For example. Make comparison
> > between transaction ids, one the transaction id asociated with the
> > update transaction and the other the transaction id asociated with the
> > newest record version on the database. If transaction ids are diferents
> > mean that other transaction have changed the record before me and i
> have
> > to show the message to ask port confirmation. I´t is posible?
>
> Hello,
>
> I don't think it is a good idea to rely on TransactionID for this,
> because they are reset if the database is restored from a backup.
>
> I am having trouble understanding what you want, but I think you have
> a record in a table that is read into some UI. After making changes,
> the user hits save and you want to make sure that no-one has modified
> the record in the meantime.
>
> If that is the case, you can use a generator and trigger to do this.
>
> Add a field to the table called UpdateNumber as a BigInt. Create a
> generator called Gen_UpdateNumber.
>
> Create a trigger before insert or update that does the following.
> NEW.UPDATENUMBER = GEN_ID(Gen_UpdateNu mber, 1);
>
> When loading the data into your UI, take note of the update number,
> and only perform the update if the UpdateNumber has not changed. If it
> has changed, you will need to design some sort of ability to merge the
> changes.
>
> A stored procedure would make this reasonably easy to do, as you could
> raise a custom exception. Remember this will not detect uncommitted
> changes to the update number, but in that case you will receive a lock
> conflict.
>
> Adam
>
>