Andrea,
2) Actual function encoding seems only required if functions cannot be
encoded like "functionName(a1, a2, ..., aN)", that is referred to
"custom encoding":
https://github.com/geotools/geotools/blob/main/modules/plugin/jdbc/jdbc-postgis/src/main/java/org/geotools/data/postgis/FilterToSqlHelper.java#L522
In PostgisFilterToSQL, visit only tries with
FilterToSqlHelper.visitFunction and, if it did NOT encode the function
in a custom manner, calls forwards to the super class
org.geotools.data.jdbc.FilterToSQL, which supports generic function
encoding:
https://github.com/geotools/geotools/blob/main/modules/plugin/jdbc/jdbc-postgis/src/main/java/org/geotools/data/postgis/PostgisFilterToSQL.java#L126
Seems like the actual problem is, that my new function's class is not
registered in the PostgreSQL Store's FilterCapabilities. However, I'm
planing a private plugin-based (SPI) solution for this. How could I
modify (extend) FilterToSqlHelper.createFilterCapabilities?
Couldn't there be a more extensible way to declare a SPI provided
function "SQL encodable" for a certain Store (e.g. PostGIS)? Maybe a tag
interface "SqlEncodable" could do that job?
Cheers
Carsten
Am 02.10.2023 um 10:03 schrieb Andrea Aime:
On Mon, Oct 2, 2023 at 9:05 AM Carsten Klein <c.kl...@datagis.com> wrote:
I managed to add a simple function "add", which returns the sum of
both its Double arguments. The add function follows the GeoTools
Function tutorial: it directly implements the Function interface
and gets created by my own FunctionFactory, which is registered
via META-INF/services/org.geotools.filter.FunctionFactory.
However, only the Java implementation is actually used.
GeoTools/GeoServer makes no attempt to encode the "add" function
in SQL when using a PostgreSQL store. What am I missing?
Because you haven't modified the database code to advertise it can
encode the function, and add the code
to perform the actual encoding. E.g., in the case of PostGIS:
1) Declaration that functions are supported
https://github.com/geotools/geotools/blob/main/modules/plugin/jdbc/jdbc-postgis/src/main/java/org/geotools/data/postgis/FilterToSqlHelper.java#L167
2) Actual function encoding:
https://github.com/geotools/geotools/blob/main/modules/plugin/jdbc/jdbc-postgis/src/main/java/org/geotools/data/postgis/FilterToSqlHelper.java#L522
Another question: most of the built-in functions do not implement
the Function interface directly but extend FunctionExpressionImpl
(which implements FunctionExpression). According to the docs,
these functions must be registered via
META-INF/services/org.geotools.api.filter.Function. So, I added a
"sub" function, returning a - b, which is based on the
FunctionExpression approach (which seems to be quite a bit more
comfortable and newer). Unfortunately, GeoServer/GeoTools seems
not to know the new "sub" function and throws an error when I try
to use that function through a WFS GetFeature request.
The docs are probably pointing you at the wrong registration file, the
functions are registered in "org.geotools.api.filter.expression.Function":
https://github.com/geotools/geotools/blob/main/modules/library/main/src/main/resources/META-INF/services/org.geotools.api.filter.expression.Function
If you spot issues in the docs please contribute fixes for it.
Cheers
Andrea
==
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