If I can recommend calling it "transform" as the name "reshape" has caused no
end of confusion. Indeed you will find the current process called "transform".
+1 on the new module however!
I am very impressed with the read and write support, nicely done.
--
Jody Garnett
On Monday, 6 August 2012 at 2:37 AM, Andrea Aime wrote:
> Hi all,
> during the last few weekends I've been working on a reshaping
> SimpleFeatureSource/SimpleFeatureStore wrapper:
> https://github.com/aaime/geotools/tree/reshape/modules/unsupported/reshape/src/main/java/org/geotools/data/reshape
> https://github.com/aaime/geotools/tree/reshape/modules/unsupported/reshape/src/test/java/org/geotools/data/reshape
>
> The work is inspired and based on Jody's reshape process, but working
> at the FeatureSource/FeatureStore level
> is more feature rich. Short feature summary:
> * wrap any source/store and rename, type cast or hide any existing
> attribute, plus the ability to add new
> attributes computed via expressions
> * the above works also around stores, and preserves their writability
> within some limitations (more on this later)
> * full support for paging and sorting, either on native properties or
> computed ones
> * fully streaming in both directions (read and write)
> * around 70% code coverage
> * better heuristics to compute/guess the type of each attribute given
> only the start schema and the expressions
> (though it's possible to force a specific target type by hand)
>
> The set of classes is relatively large, but only one is visible, a
> factory that builds the wrapper given the
> source, the target type name and the list of Definitions (which
> contain the definition of each new attribute).
> Here is an example of how it can be used:
>
> List<Definition> definitions = new ArrayList<Definition>();
> definitions.add(new Definition("geom",
> ECQL.toExpression("buffer(the_geom, 1)")));
> definitions.add(new Definition("name",
> ECQL.toExpression("strToLowercase(state_name)")));
> definitions.add(new Definition("total",
> ECQL.toExpression("male + female")));
> definitions.add(new Definition("logp",
> ECQL.toExpression("log(persons)")));
>
> SimpleFeatureSource reshaped = ReshapeFactory.reshape(STATES,
> "bstates", definitions);
>
> The set of use cases I see for this tool:
> * rename ugly attribute names coming from the database (shapefile or
> Oracle are two common sources
> of butt ugly names) without losing the ability to perform
> transactions --> this would allow to run WFS CITE
> tests against Oracle for example
> * add new attributes that were not available in the source
> * cast the type of an attribute to something else (for example, a
> String with WKT could be turned into a Geometry
> via converters, which would allow to run WFS 1.1 CITE tests against
> shapefiles too)
> * replace the geometryless store, this would require a new function
> point(x, y) and a way to invert that function
> within filters so that we can turn, say, bbox into a set of
> predicates against x and y, which is something that
> could be done within the simplifying filter visitor
> * replace the retyping data store in GeoServer with something at the
> same time more general and more
> efficient (since it wraps directly a feature source, not a store)
>
> Keeping writability is an interesting subject. So far I've been a bit
> sloppy, things can definitely be improved.
> What I have so far is a notion of Definition inversion:
>
> public List<Definition> inverse();
>
> The current code is simple and can only invert renaming, so only
> attributes that are not really computed
> can be inverted and thus be written on.
> This could be improved upon in some ways, for example:
> * have a general concept of invertible function
> * have a pluggable way to create "definition inverters" that can be
> added at runtime
> * for some limited cases, try to invert algebraic expressions of a
> single variable (e.g. a = b + 10)
>
> So far I've kept it simple, the above method can be overridden, so an
> implementor can decide to roll
> her own inversion logic.
>
> Writability control is also particularly loose right now, basically if
> we can invert at least one definition
> we come up with a writable wrapper, otherwise we return a read only one.
> I guess at the very least one should check if all the mandatory fields
> can be inverted... which brings
> an interesting riddle, what if one is not available, but I still want
> the wrapper to be writable?
> I guess the API could provide default values for the fields that get
> hidden and/or cannot be inverted.
>
> Feedback/opinions welcomed
>
> Ah, one more thing: on the branch I've linked above I've been pretty
> loose about commits, before
> merging into trunk I intend to squash them, so please don't fork it off
>
> Cheers
> Andrea
>
> --
> ==
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> more information.
> ==
>
> Ing. Andrea Aime
> @geowolf
> Technical Lead
>
> GeoSolutions S.A.S.
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> Italy
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