[Qgis-developer] Performance of QGIS expressions "attribute" and "get_feature"

[Denis Rouzaud]

Why not using joined fields ? Caching mechanism already exists there.

Le mer. 30 déc. 2015 8:18 PM, Stefan Ziegler <stefan.ziegler.de at gmail.com>
a écrit :

> Hi Nyall
>
> I compared 2.12 with current master. But I don't see an improvement.
> Opening the attribute table takes around 10 seconds for layers with approx.
> 2000 features with one virtual field (with the attribute(get_feature())
> expression). Rendering is also really slow when using rule based renderer
> on the virtual field.
>
> regards
> Stefan
>
> On Wed, Dec 30, 2015 at 7:22 PM, Nyall Dawson <nyall.dawson at gmail.com>
> wrote:
>
>>
>> On 31 Dec 2015 2:01 AM, "Stefan Ziegler" <stefan.ziegler.de at gmail.com>
>> wrote:
>> >
>> > Hi
>> >
>> > I add a virtual field to a layer with e.g. following expression
>> >
>> > attribute(get_feature('pnf_pnf','t_id',afrom),'year')
>> >
>> > This works really great. Then I'm using this new virtual field for
>> filtering the features in the rule based renderer. How does affect this the
>> rendering performance? It seems that it really slows down rendering even
>> with layers with only approx 600 features each.
>> >
>> > If so, can the speed improved with e.g. some to develop caching
>> mechanism?
>>
>> Try with the current master version - this should be MUCH faster now. I'd
>> love to hear any feedback of how you find the changes improve (or don't
>> improve!) your situation.
>>
>> Nyall
>>
>> >
>> > regards
>> > Stefan
>> >
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>
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