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

[Radim Blazek]

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).

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
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>>>
>>>
>
>