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> 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>
> 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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