Dear Jody,
Sorry for the late reply.
Thanks for the suggestions.
I will check the best way to add the CASEWHEN function in ECQL and
delegate it to the SQL engine.
Erwan
Le 22/09/2020 à 00:34, Jody Garnett a écrit :
Erwan:
If you were interested in writing a caseWhen function you could do so,
and then map it to the CASE WHEN syntax during SQL generation. We do
need the pure java function as a fallback so that the resulting
expressions work with all manner of datastores. We have functions such
as categorization which may be a good starting point.
Although it may not help your readability the function implementations
delegate to the filter implementation.
FilterFunction_greaterEqualThan implements greaterEqualThan function
using:
return Boolean.valueOf(StaticGeometry.greaterEqualThan(arg0, arg1));
StaticGeometry:
public static boolean greaterThan(Object o1, Object o2) {
return getFilterFactory2().greater(ff.literal(o1),
ff.literal(o2)).evaluate(null);
}
We do maintain an ECQL parser that extends the CQL standard. If you
wished to do the work in geotools you could look at allowing ECQL to
know about this relationship and parse ">" into a greaterEqualThan
function.
--
Jody Garnett
On Mon, 21 Sep 2020 at 03:54, Erwan Bocher <erwan.boc...@univ-ubs.fr
<mailto:erwan.boc...@univ-ubs.fr>> wrote:
Thanks Andrea,
Le 21/09/2020 à 12:18, Andrea Aime a écrit :
On Mon, Sep 21, 2020 at 11:08 AM Erwan Bocher
<erwan.boc...@univ-ubs.fr <mailto:erwan.boc...@univ-ubs.fr>> wrote:
I'd like to apply more complex expressions as the Case When
above. It
seems there is a function closed to the SQL Case When called
if_then_else.
So I try :
Expression expression =
ECQL.toExpression("if_then_else(area(THE_GEOM)>10,5, 1)");
definitions.add(new Definition("EXP", expression));
SimpleFeatureSource transformed =
TransformFactory.transform((SimpleFeatureSource) fs,
"OUTPUT_TABLE_TEST_F", definitions);
Unfortunately, it returns the following exception
Exception in thread "main"
org.geotools.filter.text.cql2.CQLException:
Encountered ">" at line 1, column 28.
Is there a way to execute nested expression with Geotools
ECQL parser ?
It is, but you're mixing filters and expressions in the wrong
way. Filters use expressions, but
they are not expressions. So something like "area(THE_GEOM)>10"
is a filter, it cannot
be nested inside an expression, only inside another filter.
There are filter functions that try to work around this
limitation, so you could write this instead:
if_then_else(greater(area(THE_GEOM), 10),5, 1)
Thanks Andrea,
if_then_else(greater(area(THE_GEOM), 10),5, 1) is a good way but
I'd like to write in plain text form as SQL does.
I'd love to see an improvement in GeoTools allowing to treat a
Filter like an Expression that returns
a boolean but... the change would not be trivial, and rife with
repercussions (would allow building
filters/expressions that are not valid anymore, not in CQL, nor
in Filter Encoding).
I understand the standard compliant pb ;-) There is a need for an
abstract and extensible language for expressions.
We will have to think about something else and maybe implement our
own parser expression.
A temporary solution would be to parse the expression with a lib
like JSQLParser (https://github.com/JSQLParser/JSqlParser) and
build a "CQL compliant" expression.
Best regards
Erwan
Cheers
Andrea
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