[Qgis-developer] virtual fields

[Nathan Woodrow]

Hey all,

The SQLite virtual table thing and these virtual fields are two different
beasts.  Both should be features.  Virtual columns should be a easy-ish one
so lets start with that.   The advantage of using SQLite virtual tables is
it would give us a high level SQL language with all the spatial functions
and the ability to do joins over any QGIS layer without too much work on
our side.  No point reinventing the wheel.   It can be slow for complex
things but if you are doing that you should move to a proper database
engine and store all your data in there.

- Nathan


On Tue, Mar 4, 2014 at 7:09 AM, Matthias Kuhn <matthias.kuhn at gmx.ch> wrote:

> On Mon 03 Mär 2014 17:55:06 CET, Denis Rouzaud wrote:
> >
> > On 03. 03. 14 16:42, Matthias Kuhn wrote:
> >> On a similar note see this recent thread [1] which should be able to
> >> provide this kind of functionality. I don't know if Nahtan has
> >> already started to implement his POC.
> > What would be the advantage of such a beast?
> > Is it the caching?
>
> Not sure about dis- and atvantages. I just thought I'd throw it in :-)
>
> Honestly: injecting expression fields at the vectorlayeriterator level
> sounds like a good and flexible approach. There are quite a few tools
> which still operate on vlayer.provider.getFeatures() etc. Those will
> unfortunately not be able to benefit from such an approach.
> The virtual layer approach discussed in the other thread is more like a
> Swiss army knife for a couple of different things.
>
> I didn't spend much thoughts on all of this, please read it with a
> pinch of salt.
>
> Best
> Matthias
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