Rename VALUE to ARRAY_GET, declare rql to sql mapping directly in FunctionDescr (closes #3036180)

schema/_regroc.postgres.sql

-/* -*- sql -*-
-
-   postgres specific registered procedures,
-   require the plpgsql language installed
-
-add the VALUE function to be able to query the postgres arrays
-in RQL query, example below:
-
-   Any X WHERE X is TimeSerie, X serie S HAVING VALUE(S, 10)>3
-
-*/
-
-CREATE OR REPLACE FUNCTION VALUE(ar1 integer[], indice integer) RETURNS float
-AS $$
-BEGIN
-return ar1[indice];
-END;
-$$ LANGUAGE plpgsql;
\ No newline at end of file

site_cubicweb.py

@@ -40,11 +40,14 @@ sqlitehelper.TYPE_CONVERTERS['FloatArray'] = json.dumps
 
 from rql.utils import register_function
 
-class VALUE(FunctionDescr):
+class ARRAY_GET(FunctionDescr):
     minargs = 2
     maxargs = 2
     supported_backends = ('postgres',)
     rtype = 'Float'
 
+    def as_sql_postgres(self, args):
+        return "%s[%s]" % (args[0], args[1])
 
-register_function(VALUE)
+
+register_function(ARRAY_GET)