[Qgis-developer] Change the query of a query layer (postgis)

[Enrico Ferreguti]

Hi Olivier,
datasource changing is a feature that I really miss and wait from longtime.
Every Qgis new release I checked without success if the properties
datasource string is editable. I recently found the hack you report (
https://geogear.wordpress.som/2015/05/15/changing-qgis-layer-datasource-with-python/)
that I verify to be working up to Wien 2.8.2. Till 2.9 the code crash qgis.
Reading your post I realized that a new QgsVectorLayer method has appeared:
setDatasource. Wow! Perhaps the waiting is going to be over....

Regards,

Enrico Ferreguti.

2015-06-17 16:45 GMT+02:00 Olivier Dalang <olivier.dalang at gmail.com>:

> Hi Enrico,
>
> Hmm I didn't think of that, thanks for the idea ! But I can't use it since
> I may have several user at once.
>
> Best,
>
> Olivier
>
> 2015-06-17 16:03 GMT+02:00 enricofer <enricofer at gmail.com>:
>
>> Hi Olivier,
>> In your case, I think that the best way to do this is to create a view
>> from the sql query and load it as layer, than, when qslider changes, change
>> the view definition with "ALTER VIEW"  and reload the layer.
>>
>> Regards,
>>
>> Enrico Ferreguti
>>
>> Il giorno 17/giu/2015, alle ore 14:29, olivier [via OSGeo.org] <[hidden
>> email] <http:///user/SendEmail.jtp?type=node&node=5211452&i=0>> ha
>> scritto:
>>
>> Hi !
>>
>> Is it possible to change the query of a postgis query layer in python
>> without reloading the project ?
>>
>> The goal is to have a parameter in my query that I'd be able to change
>> with a slider.
>>
>> I tried the QgsVectorLayer.setDataSource() method, but it makes QGis
>> crash.
>> I tried the workaround described here (
>> http://gis.stackexchange.com/questions/62610/changing-data-source-of-layer-in-qgis
>> ), writing and reading the XML file, but it also makes QGis crash.
>>
>> If not possible, is there a serious limitation behind this, or is the
>> feature just missing/bugged ?
>>
>> Example :
>>
>> I have this query loaded as a layer:
>>
>> "SELECT id, name, ST_Buffer(geom,25) as geom FROM my_table"
>>
>> But I want to be able to change the hardcoded buffer from 25 to some
>> value from a QSlider.
>>
>> Thanks!
>>
>> Olivier
>>
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