[Interest] SQLite

[Jason H]

I once wrote a ORM that took an XML definition, and spat out QObject-derived classes that provided QObject QPROPERTY to SQLite database mappings. So it would create the SQL schema, the source files (.cpp/h) had support for transactions and rollbacks. I don't know how useful it would be for anyone because of the XML schema. I wound't want to impose that on anyone because that XML schema was the output of another process. But I think it could be the foundation for a simple object persistence layer.

> Sent: Thursday, May 28, 2015 at 3:29 AM
> From: "Graham Labdon" <Graham.Labdon at avalonsciences.com>
> To: "Bo Thorsen" <bo at vikingsoft.eu>, "interest at qt-project.org" <interest at qt-project.org>
> Subject: Re: [Interest] SQLite
>
> Hi Bo
> It would be really interesting to see your sources and I would be grateful if you could email them to me
> 
> Thanks
> 
> Graham
> 
> -----Original Message-----
> From: Bo Thorsen [mailto:bo at vikingsoft.eu] 
> Sent: 27 May 2015 21:56
> To: interest at qt-project.org; Graham Labdon
> Subject: Re: [Interest] SQLite
> 
> Den 27-05-2015 kl. 10:51 skrev André Somers:
> > Graham Labdon schreef op 27-5-2015 om 09:39:
> >> Hi
> >> I am planning to use a SQLite database in my application to store application data.
> >> The application is large and complex so we are taking a phased delivery approach. This will mean that the structure of the database will change over time and that we need to provide backwards compatibility.
> >> So, what I need is some way to create a versioning system and a way of converting old format databases to the current format.
> >> I would be grateful if anyone could suggest a good approach to this
> >>
> >> Thanks
> >> _______________________________________________
> >> Interest mailing list
> >> Interest at qt-project.org
> >> http://lists.qt-project.org/mailman/listinfo/interest
>  >
> > We do it manually. We keep a data version number in the database 
> > properties, which you can set and get via a pragma. Then, we have a 
> > list of updater objects that can update a database from one version to 
> > the/a next using a script. For every database change we need to make, 
> > we up the version number we expect, update the code to create a new 
> > database and write an updater script from the previous version. We run 
> > the scripts we need to update to the version expected by the software 
> > at startup. So, if you run the software against a version 7 database 
> > and the software expects version 10, it will go through the scripts 
> > looking for a script that updates version 7. The updater that takes a 
> > version 7 then updates to version 8, so the software will look for a 
> > script that takes a version 8 database. This updater can then update 
> > to version 10 in for instance, skipping version 9 that may have been 
> > faulty in some sense. It is quite easy to extend and reasonably 
> > flexible in terms of making it possible to create scripts that skip 
> > version numbers if that makes sense, but not make it mandatory to 
> > write a separate script between each possible version.
> >
> > Note that we don't support going backwards. That sometimes causes 
> > problems when clients want to reinstall a previous version because of 
> > some regression.
> 
> I have a similar approach to this, except that I code generate the db code. Some tables can be generated based on the contents of other tables, so those are just wiped when upgrading a table to a new version. 
> For those that can't be generated, I have to implement an upgrade function.
> 
> I have been meaning to clean this up a bit and allow others to use it, but so far haven't found the time.
> 
> Graham (or anyone else who might be interested), if you want to see it, I could send you the sources for the code generator.
> 
> Bo.
> 
> --
> Viking Software
> Qt and C++ developers for hire
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