[fpc-pascal] Documentation for sqldb

[Joost van der Sluis]

On Fri, 2007-06-22 at 10:43 +1000, John wrote:
> Joost van der Sluis wrote:
> 
> > IN principle you can set ReadOnly to false and ParseSQL to true. That
> > way sqldb tries to parse your query. If it's a simple 'select * from
> > table' the TSQLQuery will be updateable. It automatically generates
> > update/delete and insert queries. For the 'where' clause is uses  by
> > default the primary key of the table. (That's a setting, upWhereKeyOnly)
> >
> > For example: 'delete * from table where pk=:old_pk'
> >
> > If you edit some data, those changes will be stored in an updatebuffer.
> > With TSQLQuery.CancelUpdates all those changes are lost. But if you
> > call .ApplyUpdates, it will execute one query for every changed record.
> > (That could be a insert, update or delete query) 
> >   
> So if I change some field values and post the record, that changed data 
> goes into the update buffer - of TBufDataset ?  I should then be able to 
> accumulate a few changes of these, and then, in code, call 
> TSQLQuery.ApplyUpdate, and it should be sent to the database ?  Should 
> this also commit at the database level, or do I have to do this ?  
> (I think I tried this, but didn't pursue it very far, because I wasn't 
> sure if it even should work)

You have still to commit the database-transaction.
(SQLQuery.Transaction.commit(retaining)) And yes, the buffer is handled
by TBufDataset.

> Would it be feasible / sensible to call ApplyUpdate from an AfterPost 
> event handler ?  

Yes, you could do that. But that could generate a lot of sql-traffic.
Maybe in an after-scroll is a better idea.

> > Those are the basics. If you have questions, ask them here. And if you
> > have any time, please document it somewhere on the wiki. ;)
> I will, if I get to the point of thinking I understand it enough to not 
> make a fool of myself!

Just start it, others will correct mistakes if needed.

Joost