[QGIS-Developer] How to update change the datasource of already existing layer

[Ivan Ivanov]

Hi, Nyall,

I'm developing a plugin with a lot of internal layers, that are being
(re)created on user interaction.

There are multiple event listeners attached to a layer, as well as passed
around to different functions and might have custom styles. At some point,
I want to replace the layer entirely with another one (result from an
algorithm).

To solve this, I came up with three solutions, maybe there are more:
One option to achieve this is to copy all the features from the new layer
and put them in the first one, but the layers might be very big and I'm
afraid it would be a problem.
The second option that I'm currently using is to recreate all the event
listeners on the new layer and replace it from the layer tree. This is
okayish and it works.
The third option is to set a new data source, as I thought it's the most
optimal one, however, when the layer has two uids it's practically broken.

I got some inspiration from here:
https://github.com/enricofer/changeDataSource/blob/master/setdatasource.py#L175-L206
directly editing the XML but the result is the same - double ids. I checked
this plugin because I'm sure it used to work in 3.2 (currently having 3.6.3
on Ubuntu).

Best,
Ivan



On Fri, 14 Jun 2019 at 01:21, Nyall Dawson <nyall.dawson at gmail.com> wrote:

> On Wed, 12 Jun 2019 at 10:09, Ivan Ivanov <suricactus at gmail.com> wrote:
> >
> > I fixed it. Sorry for the inconvenience:
> >
> > layer1 = QgsVectorLayer('Polygon?crs=epsg:32612', 'layer2', 'memory')
> > layer2 = QgsVectorLayer('Polygon?crs=epsg:32612', 'layer1', 'memory')
> >
> > print(layer1.source())
> > print(layer2.source())
> > layer1.setDataSource(layer2.source(), layer2.name(),
> layer2.dataProvider().name())
> > print(layer1.source())
>
> I agree that the results of this output look odd - but what exactly
> are you trying to achieve here?
>
> Nyall
>
> >
> > On Wed, 12 Jun 2019 at 00:28, Nyall Dawson <nyall.dawson at gmail.com>
> wrote:
> >>
> >> On Tue, 11 Jun 2019 at 15:06, Ivan Ivanov <suricactus at gmail.com> wrote:
> >> >
> >> > Hello,
> >> >
> >> >
> >> > Can you give me some idea why I'm getting two uids in the layer's
> source? And also how I can fix this because now the layer just disappears
> from the map canvas. (all layers are isValid() = True)
> >> >
> >> > oldLayer.source()
> >> > #
> MultiLineString?crs=EPSG:32737&field=fid:integer(0,0)&uid={6cd1f176-9c05-4d2a-961a-3143a8fa422b}
> >> >
> >> > newLayer = processing.run('save:selectedfeatures', {
> >> >     'INPUT': oldLayer,
> >> >     'OUTPUT': 'memory:newLayer'
> >> > )
> >> >
> >> > oldLayer.setDataSource(newLayer.source(), oldLayer.name(),
> newLayer.dataProvider().name())
> >> >
> >> > newLayer.source()
> >> > #
> MultiLineString?crs=EPSG:32737&field=fid:integer(0,0)&uid={d36aff88-4248-4ffb-be2f-2ac1891ac26d}
> >> > oldLayer.source()
> >> >
> >> > # WRONG, I would expect the same as above. Also, the uid is
> completely new.
> >> > #
> MultiLineString?crs=EPSG:32737&field=fid:integer(0,0)&uid={d36aff88-4248-4ffb-be2f-2ac1891ac26d}&uid={3422de07-cf38-4249-af55-23c7d9779daf}
> >>
> >> Hi Ivan,
> >>
> >> Your code seems incomplete and has some syntax errors -- maybe it
> >> wasn't copied correctly? Can you repost please?
> >>
> >> Nyall
>
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