Hi Andrea and Jody,
Thanks for the proposals and comments.
Le 23/12/2020 à 09:40, Andrea Aime a écrit :
Agreed with Jody, should be a new set of functions, you can delegate
to the old one if needed (but not fully, the
Name returned cannot be the same). Should be doable with just a
factory and a generic function wrapper instanciated
with the target function and the new name to be used... as long as the
semantic of the function is the same
(I'd expect it to be, but wouldn't just assume it).
This is my idea also. I will check all the functions to look on the
semantic(s) and the algorithm(s).
What is worrying me a bit is, to what point do you want to push this?
Having them in CQL is fine. Having a 1-1 translation
down in SQL, done in FilterToSQL, the class shared by all databases,
is not: some databases would not natively support
the functions anyways. Examples are GeoTools own H2 store, Oracle with
Locator extension (afaik), GeoPackage.
So, the eventual encoding down in SQL should be left to a case by case
decision.
At OGC spec level there is a lake of definition about a standardized
expression language that permits to query a data-source. CQL
implementation in Geotools solved partially this issue. It's quite
comfortable and a very good idea to reuse CQL text language to offer a
way to query any kind of feature sources. Nevertheless, it can be
confusing for a user to have on one side functions whose names are
standardized (and that he can use in a language like SQL) and on the
other side functions that depend on vendor spec or a specific usage.
Let's take the case of the geomlength function in GT that returns the
length of a geometry. If I'm not wrong, the compliant name in ISO/TC
211, ISO /IEC JTC 1/SC 32/WG 4 - SQL MM or OGC -SFS is length, prefixed
with the ST_ for SQL part. I understand that CQL is based on Filter
Encoding Spec so using contains, intersects without st_ are absolutely
compliant with the spec.
But because the use of CQL can be extended to any kind of datasources
not only set of features from a WFS service, I think it'd be nice to
offer a way to use the SFS function names in CQL. The impact will be
positive since a user who manipulates the spatial SQL will not be lost
in the CQL domain. Of course it will not have the same possibilities
than SQL to write complex expressions (e.g subquery or window
expressions), but for basic "SELECT" it will be enough.
This is my idea : add support to SFS names in CQL (filter and
expression) without breaking anything in the parser ;-)
I'd like to push CQL in the next feature2D style encoding POC based on
SymCore to have this kind of encoding :
https://twitter.com/OrbisGIS/status/1339904475004342274
Cheers and Merry Christmas with your family and friends.
Erwan
Cheers
Andrea
On Wed, Dec 23, 2020 at 3:41 AM Jody Garnett <jody.garn...@gmail.com
<mailto:jody.garn...@gmail.com>> wrote:
Yep, that is just the only reference we have mapping from SFSQL to
geotools functions right now.
And yeah, you should be able to extend not geotools function, but
geotools function factory.
1. Make a new FunctionFactory listing the SFSQL function names
2. Make a Function wrapper implementation
3. Use the wrapper to create any SFSQL function name instance
requested
--
Jody Garnett
On Tue, 22 Dec 2020 at 08:42, Erwan Bocher
<erwan.boc...@univ-ubs.fr <mailto:erwan.boc...@univ-ubs.fr>> wrote:
Jody,
I know that but I want to use the SFS function names in ECQL.
If I understand well the way to do that is to extend the
current geotools function and filter on my side and register
them ?
Erwan
Le 22/12/2020 à 08:47, Jody Garnett a écrit :
Erwan:
It depends a bit on each database, you will find that many of
them implement the SFSQL specification.
Here is one for PostGIS:
https://github.com/geotools/geotools/blob/master/modules/plugin/jdbc/jdbc-postgis/src/main/java/org/geotools/data/postgis/FilterToSqlHelper.java
--
Jody Garnett
On Mon, 7 Dec 2020 at 07:50, Erwan Bocher
<erwan.boc...@univ-ubs.fr <mailto:erwan.boc...@univ-ubs.fr>>
wrote:
Hi,
I have a first prototype to convert SQL expression to
Geotools
Expression available as a draft here
https://github.com/orbisgis/orbisgis/pull/1404
Spatial databases use ST_ prefix to define spatial
function. e.g
st_area, st_centroid
Geotools expression and filter function doesn't.
I added a workaround in the sql to expression parser to
check when the
sql expression contains a "st_" function and rename it to
a geotools
representation.
I'd like to known if there is a simple way to aliasing
filter function
in geotools and write something like that
st_area(the_geom) >1000 instead of area(the_geom) >1000
best regards
Erwan
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