[mapserver-users] [SOLVED] Re: Filtering NULL values from Postgis Layer in Mapserver 7

[deduikertjes]

Steve, 

thank you


Lime, Steve D (MNIT) wrote
> The filter option is still there - it's just implemented as a processing
> option instead. So what was:
> 
>   FILTER 'myitem != NULL'
> 
> Becomes:
> 
>   PROCESSING 'NATIVE_FILTER=myitem != NULL'
>   
> Steve  

I can confirm that making the FILTER a PROCESSING option indeed works, even
with runtime substitution. (using = NULL does not work, IS NULL must be
used)

So the mapserver6 style line:
   FILTER (NOT (%MY_VAR1% IS NULL OR %MY_VAR2% IS NULL)) 
in mapserver 7 becomes:
   PROCESSING 'NATIVE_FILTER=(NOT (%MY_VAR1% IS NULL OR %MY_VAR2% IS NULL))'

So I summarize:
   - CLASS EXPRESSIONS will treat NULL values in numerical fields as zero
(and I presume it does the same for empty numeric fields in shapefiles). It
is not possible to prevent this behaviour.
   - To prevent NULL values from being rendered a FILTER must be applied, or
a subselect in the DATA statement must be used.
   - In mapserver 6 that can be a native filter with a syntax like FILTER
(NOT (%MY_VAR1% IS NULL OR %MY_VAR2% IS NULL)) 
   - In mapserver 7 that filter must be added as a processing option with a
syntax like PROCESSING 'NATIVE_FILTER=(NOT (%MY_VAR1% IS NULL OR %MY_VAR2%
IS NULL))'

It still would be very nice to have an option to ignore empty fields/ NULL
values/ missing values like -9999 with a single config option. Shall I file
a feature request for that?

MArco




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