Re: [Geotools-gt2-users] Sorting shapefile

[Andrea A. <aa...@op...>]

jericks ha scritto:
> I am trying to sort a shapefile or ArcSDE layer by an attribute.  I first
> tried adding a SortBy to a DefaultQuery, but the shapefile throws an error
> and the ArcSDE layer fails silently.  Next, I tried reading my FeatureSource
> into an ArrayList of SimpleFeatures, sorting them using a Comparator, and
> then writing the ArrayList back to an output FeatureStore, but the order is
> not preserved.  What is the correct way of sorting a FeatureSource?

Native sorting is not supported on all stores, in particular, only
database backends do... not sure what goes on in SDE.
You can check at runtime if a feature source
supports sorting on a certain field by using 
FeatureSource.getQueryCapabilities.supportsSorting(SortBy[]).

As for preserving order in writes, there is basically only shapefile
that do support it, but it's just an accident of how the writing
occurs. SDE is free to keep whatever order it wants storage wise,
and when you retrieve data the order will be very much dependent
on what indexes are used to execute the query.

So I guess in the end what you need is sort support in SDE.
By looking at the code in SDE it would seem sorting in never
supported (the query capabilities seem to always return false to
the above cited methos), but I may be wrong. I've cc'ed the module
maintainer, he should know more.

Cheers
Andrea


-- 
Andrea Aime
OpenGeo - http://opengeo.org
Expert service straight from the developers.