[Qgis-developer] Expression based labeling

[Martin Dobias]

On Fri, Oct 28, 2011 at 1:33 PM, Sandro Santilli <strk at keybit.net> wrote:
> On Fri, Oct 28, 2011 at 12:23:24PM -0300, Martin Dobias wrote:
>> On Fri, Oct 28, 2011 at 4:15 AM, Sandro Santilli <strk at keybit.net> wrote:
>> > Would it make sense to abstract provider-specific IDs so that the
>> > [0, N-1] range holds for everyone ?
>>
>> This is actually done within attribute table - we store feature IDs
>> for the range [0,N-1] so that we can later access the feature data by
>> row number. But that comes at an additional price: the layer has to be
>> scanned first in order to obtain the mapping and it has to be updated
>> whenever some changes to the layer are done.
>>
>> What would be the requirements of such provider-specific IDs? What to
>> do when a feature is deleted? If we recreate the mapping, some IDs
>> stored by users would change, leading to problems if the user stores
>> them as references to features. If we keep the original mapping, then
>> it may contain holes and therefore the convenient [0, N-1] range would
>> not be valid.
>
> What happens if you delete a feature from a shapefile ?

Apparently OGR only marks the feature as deleted in DBF, other IDs are
not changed.

Martin