[PyQt] QSql lastError() must be called BEFORE exec_() ??

[Andreas Pakulat]

On 05.09.09 20:43:26, Mario Daniel Carugno wrote:
> 2009/9/5 Andreas Pakulat <apaku at gmx.de>:
> > On 04.09.09 17:23:32, Mario Daniel Carugno wrote:
> >> Hi list, i'm coding my first PyQt4-Sql application, and i can't
> >> understand a strange behavior.
> >> I'll write a snippet of code with an erroneous Sql syntax, and i hope
> >> then to catch the error
> >> text and display it, in order to know what happened:
> >>
> >> query = QSqlQuery()
> >> query.prepare("insert inta table (name) values ('myname')")  # note
> >> that 'inta' is an error
> >> query.exec_()
> >> if query.isActive() == False:
> >>    print "ERRSQL " + str(g_session.db.lastError().text())
> >>
> >> And this do not work ! It is not displaying any text.
> >> To get it work, i must get the error string BEFORE the execution of the query !!
> >>
> >> query = QSqlQuery()
> >> query.prepare("insert inta table (name) values ('myname')")  # i made
> >> an erroneous sql
> >> query.exec_()
> >> errorstr = str(query.lastError().text())
> >> if query.isActive() == False:
> >>    print "ERRSQL " + errorstr
> >>
> >> Is that behavior normal ??
> >
> > Yes.
> >
> >> How can PyQt get the error's text BEFORE executing the sql statement ?
> >
> > It doesn't. The errors is fetched _after_ executing the sql statement
> > because you're executing the sql statement in the line that calls
> > exec_(). If you look at the API docs it pretty clearly states that
> > this method executes the prepared sql statement.
> >
> > The reason the error can be fetched at this point already is because
> > there's a syntax error in your SQL, thats usually checked very very
> > early during statement execution, hence after the exec_() call the error
> > is already set.
> >
> > If you'd have a long-running query (huge resultset from a select) and
> > that throws some kind of error way after it was started you'd probably
> > get the error only after isActive returns false.
> >
> So it means that sometimes i must get error strings before exec_() and
> sometimes i have to do it after exec_() ?

No, you're always fetching the error string _after_ exec_(). You're
doing that in both cases. But you should fetch an error string before
asking query.isActive(). As that may apparently overwrite lastError().

Andreas

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