[QGIS-Developer] QGIS/OGR: FeatureIds reassigned on write to data provider?

[Sandro Mani]

On 05.07.2017 14:56, Sandro Mani wrote:
>>
>> That could potentially be done using the current OGR API. Basically 
>> in pseudo code, to execute before executing REPACK
>>
>> OGR_L_ResetReading(layer)
>>
>> char** ignored_fields = CSLAddString(NULL, "OGR_GEOMETRY" );
>>
>> OGR_L_SetIgnoredFields( layer, ignored_fields); // for performance.
>>
>> CSLDestroy(ignored_fields);
>>
>> OGR_L_SetAttributeFilter( layer, NULL )
>>
>> OGR_L_SetSpatialFilter( layer, NULL )
>>
>> std::map<GIntBig, GIntBig> mapOldIdToNewId;
>>
>> GIntBig newId = 0;
>>
>> while( feature = OGR_L_GetNextFeature(layer) )
>>
>> {
>>
>> mapOldIdToNewId[OGR_F_GetFID(feature)] = newId;
>>
>> newId ++;
>>
>> OGR_F_destroy(feature);
>>
>> }
>>
>> OGR_L_SetIgnoredFields( layer, NULL );
>>
> Ok cool, that sounds like a plan - I'll give it a shot.
>
Hmm so while on the provider side it works well, for the geometry 
checker it is turning out to be pretty hard to deal with the changing 
feature ids (just to cite one example: error fixed by merging geometry 
of feature 10 with that of 11, results in {deleted: 10, updated: 11}, 
but after the feature id adjustment this would read {deleted: 10, 
updated: 10}, meaning one would need to keep track that deleted: 10 
refers to the old featureid). Not saying that it isn't doable, but the 
complexitiy of properly handling the feature id changes is non-trivial.

So, other suggestion: any objections if I add a method to 
QgsVectorDataProvider to temporarily freeze repacking? I could also add 
a notification informing the user that the shapefile should not be used 
in other applications while repacking is frozen.

Sandro
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