[Lazarus] What is a TSQLTransaction and why do I need one?

michael.vancanneyt at wisa.be michael.vancanneyt at wisa.be
Wed Dec 1 17:38:53 CET 2010

On Wed, 1 Dec 2010, Joost van der Sluis wrote:

> On Wed, 2010-12-01 at 16:01 +0100, michael.vancanneyt at wisa.be wrote:
>> On Wed, 1 Dec 2010, Joost van der Sluis wrote:
>>>> Is there somewhere I can hook into the TSQLQuery to (a) see exactly what
>>>> query was passed to the server (b) collect any error text and (c) get
>>>> execution timing?
>>> a) Easiest is to use the database-client's log mechanism. (If there is
>>> any). Else you can change the TPQConnection.Preparestatement function.
>>> The 'buf' parameter is the actual query. But as you'll see it also adds
>>> some more to the query, so it opens a cursor, before it is send to the
>>> database-server.
>>> b) Ehm.. the error-text is in the exception?
>>> c) Hook into TPQConnection.PrepareStatement and TPQCOnnection.Execute
>> I am a firm proponent of putting a unified mechanism for a) and c) in
>> TSQLQuery/TSQLConnection, and have, in fact, a patch ready for this
>> (it implements a simple event mechanism for the log).
> That's a no-brainer. It could als use TCustomApplication.Log, if
> Customapplication is assigned. Or, add events before and after an
> statement is prepared, executed or unprepared. (And when data is
> fetched)

That would create a dependency on custapp. If it isn't there yet, I would
not introduce it.

I have now

TDBEventType = (detPrepare,detExecute,detFetch,detCommit);
TDBLogNotifyEvent = Procedure (Sender : TSQLConnection; EventType : TDBEventType; Const Msg : String) of object;

And in TSQLConnection:

   Property OnLog : TDBLogNotifyEvent Read FOnLog Write FOnLog;

But we can provide a unit that, when included, logs all queries 
to custapp through a global hook. In fact, I think that's a good 

If it is OK with you, I'll implement and commit it Friday ?

> But should we add this code in the connection-objects for each db-type,
> or in the code in the sqldb unit?

In the sqldb unit, of course.


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