QSqlTableModel & treeview

[janEUcitzen]

Hi

I am relatively new to Qt so let me start by excusing for not knowing the "obvious".

I have a mysql table (actually a complicated view) with 4.000.000 entries or approx. 40Gb worth of data.

I want to make an application where the user can browse through these data, and found QSqlTableModel together with Qtreeview perfect for the job...

however how do I stop QSqltableModel from trying to read all 4.000.000 entries in one chunck ???? (I do not have enough ram on my notebook).

What I actually looked for was a widget/model, with a treeview layout, and with buttons for next chunk, previous chunk....but I have not been able to find any example code ?

Am I on the right track, or do I have to programm everything myself ??

thanks in advance for a reply...

jan

[caduel]

I thought QSqlTableModel etc read data on demand?
(I.e. when you scroll down, further data is requested...)
Have you checked that all the data is read right at the start?

[janEUcitzen]

Hi.

that was my understanding too...but after my PC melted down...I ran a mysql trace, to see the statements issued..

and Qt just sent a normal select...... without the "limit" parameter, meaning mysql collects all data at once...and the treeview explodes.

but admitted I have also not found anywhere to define how big chuncks treeview should display...there does not seem to be a setCount(), displayNext(), displayPrevious() methods...

jan

[caduel]

* check QSqlQueryModel::fetchMore()
* check if your database driver has that feature

[janEUcitzen]

hi.

I use the standard mysql driver supplied with Qt4.4.1...

If I look at the documentation of fetchMore is says:

Fetches more rows from a database. This only affects databases that don't report back the size of a query (see QSqlDriver::hasFeature()).

and mysql reports the rowcount back...just to be sure I checked in the source of the driver, and it sets the feature..

but do you know if I can force that feature off, with the standard mysql driver ??

jan

[janus]

Hi,

there is an app at qt-apps.org (http://www.qt-apps.org/content/show.php/Thetyss+Data+Browser?content=76696) that does not use a treeview but seems to deal with a similar problem (huge tables). Since I am working on something similar i allways wanted to take a look at it. But I haven't so far ... Maybe this is helpfull for you as well.

[janEUcitzen]

HI.

thanks a lot, I just had a swift look at the code, and it seems to do the job...at least enough that I can adapt the rest. So now I have some interesting things to do in the weekend.

thanks again
jan