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

[Stefan Ziegler]

Thanks for the hint. This works perfect. But: the main idea was to avoid
creating "new" fields in the layer (virtual fields or joined ones) but only
using the expression for rendering.

Stefan

On Wed, Dec 30, 2015 at 9:02 PM, Denis Rouzaud <denis.rouzaud at gmail.com>
wrote:

> 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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