[Qgis-developer] Keep track of features in memory provider

[Matthias Kuhn]

On 19.11.2013 09:12, Radim Blazek wrote:
> On Mon, Nov 18, 2013 at 8:58 PM, Matthias Kuhn <matthias.kuhn at gmx.ch> wrote:
>>>> As far as I know, currently the most appropriate thing is to use
>>>> layer.dataProvider().addFeatures() and to skip the edit buffer.
>>> That is what I am doing, but QgsMemoryProvider::addFeatures()
>>> overwrites original feature id.
>> It will return a (list of) new feature with the real id:
>>
>> status, features = l.dataProvider().addFeatures( feats )
>> features[0].id()
> I see, that is what I was looking for, thanks.
>
>>> Another issue with writing directly to provider is, that attribute
>>> table is not updated. So how to programmatically change features
>>> avoiding edit buffer?
>> I think we should rather fix this issue. I would very much like
>> QgsVectorLayer to emit a signal, when it commits the features and
>> changes their ids.
>>
>> QgsVectorLayer::featureIdsChanged( QMap< QgsFeatureId, QgsFeatureId )
>>
>> So you could connect to this and would not be forced to directly
>> interact with the dataprovider.
> It would be nice to be able to modify data through vector layer but
>  - without showing editing mode in legend
>  - avoiding editing buffer (don't need to fiddle with id changes)
>  - modify more features in one call, i.e. the same methods as provider
> (hopefully to make efficient sending signals to attribute table)
>
> OTOH, provider should also have a chance to let layer know about
> changes, for example dynamic layers or ongoing discussion about
> topological editing (multiple layer with the same source).

Agreed, I don't think this is possible yet. This would solve some of the
problems you outlined above.

Concerning the efficiency of sending signals to the attribute table, I
think it would be good, if besides the QgsVectorLayer::featureAdded(
QgsFeatureId ) signal another signal QgsVectorLayer::featureAdded(
QgsFeature& feature ) would be introduced. This way, it would not be
necessary to create a new feature request with a FilterFID for every new
feature the table receives. I guess this would already avoid a lot of
overhead. And then we could also send batch signals like we do for
QgsVectorLayer::selectionChanged so there would be only one signal
instead of one per feature.

Matthias

>
> Radim
>
>> Matthias
>>
>>> Radim
>>>
>>>> But I
>>>> think that layers should broadcast information about changing feature
>>>> ids. This is not a problem unique to the memory provider.
>>>>
>>>> Matthias
>>>>
>>>> On Mon 18 Nov 2013 17:25:39 CET, Radim Blazek wrote:
>>>>> Is there a trick how to keep track of features added to memory provider?
>>>>>
>>>>> Say that feature with id is added to a memory provider. Original id is
>>>>> overwritten by the memory provider. How to access the feature in the
>>>>> provider by original id without additional attribute or hacks like
>>>>> counting mNextFeatureId outside the provider.
>>>>>
>>>>> Radim
>>>>> _______________________________________________
>>>>> Qgis-developer mailing list
>>>>> Qgis-developer at lists.osgeo.org
>>>>> http://lists.osgeo.org/mailman/listinfo/qgis-developer
>>>>
>>