[xsd-users] sorting of a sequence of elements when IDs are contained, duplicate_id exception

[Boris Kolpackov]

Hi Jan,

Jan Klimke <jan.klimke at hpi.uni-potsdam.de> writes:

> The problem is when i call
> 
> std::sort(tour->getTourSection().begin(), tour->getTourSection().end(),
> compareTourSectionBySectionNumber);
> 
> where tourSection is a sequence of gml:FeaturePropertyType, a
> duplicate_id exception is thrown. This probably happens because of the
> gml:id of the entities is copied when a position switch in the sequence
> is necessary.

Hm, that's an interesting problem. I think you are right about what
happens: std::sort() first inserts a new copy and then removes the
old one. So you end up with two objects with the same ID in the tree.

I can't think of anything better than these two solutions:

(1) Implement your own sort where you first remove the old element
    from the sequence and then insert the new one.

(2) Copy the contents of the sequence into another, "free-standing"
    sequence which is not part of any object model. You can then sort
    that sequence and copy the result back. There is quite a bit of
    copying with this approach:

    TourSectionContainer tmp = tour->getTourSection();
    std::sort(tmp.begin(), tmp.end(), compareTourSectionBySectionNumber);
    tour->getTourSection() = tmp;

    Note that using swap() here won't work.

Boris