I like the Transformation process/api quite a lot too. So I think a
reasonable approach to implementing this would be to intercept the Query in
the FeatureSource.getFeatures(Query) method and check if the listed
properties are Definitions/Transformations. If they are then rewrite the
Query and process the transformations in the native optimal manner. The
only thing I don't like is that the transformation has to be decoded from
string form rather than being passed in as a data structure. See any
obvious problems with this approach? Any other recommendations?
Thanks,
Anthony
On Sat, Apr 12, 2014 at 12:37 PM, Andrea Aime
<[email protected]>wrote:
> On Sat, Apr 12, 2014 at 5:10 PM, Anthony F <[email protected]> wrote:
>
>> In the Query api, I can specify a subset of columns that I would like
>> returned as part of my query. It would be useful if I could pass in a list
>> of transform definitions or expressions and have the underlying database
>> execute the transformations. This would be similar to a SQL projection
>> such as
>>
>> 'select concat('id', 'name') as newname, buffer(the_geom, 0.1) as bufgeom
>> from mygeomtable where within(the_geom, polygonWKT)'
>>
>> Is there a simple way to do this sort of thing that I have overlooked?
>> I've been digging around in the Query api and the Transform process code to
>> see if this is possible. I need a way to send the list of transform
>> definitions to the underlying DataStore (in this case GeoMesa) so that it
>> can execute the transformation in an optimal way. In the GeoMesa case, we
>> would be able to leverage distributed parallel processing to compute an
>> computationally expensive transformation.
>>
>
> In the case of the relational databases, we have a custom API that allows
> to define "virtual tables", where you really
> just provide the sql to be run, and the store will use it as a source of
> records (and will wrap it in a larger query by
> stashing it as a subquery in the from clause).
>
> It's then up to the application to recognize that specific extension, for
> example GeoServer has custom code targetting
> the JDBCDataStore family.
> But no, there is no general mechanism.
>
> Cheers
> Andrea
>
> --
> ==
> Meet us at GEO Business 2014! in London! Visit http://goo.gl/fES3aK
> for more information.
> ==
>
> Ing. Andrea Aime
> @geowolf
> Technical Lead
>
> GeoSolutions S.A.S.
> Via Poggio alle Viti 1187
> 55054 Massarosa (LU)
> Italy
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>
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>
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>
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