[mapserver-dev] Regression test issue: NULLs in shapefiles...

[Even Rouault]

Le lundi 25 août 2014 17:42:26, Lime, Steve D (MNIT) a écrit :
> Hi all: I'm trying to debug a failing CITE test
> (wfs_200_cite_filter_like.xml) for RFC 91 that uses PropertyIsLike. In
> master that resolves to "item like '%'"  for OGR and other databases. For
> a shapefile it resolves to "item ~ '.*'". In the test shapefile data there
> are a bunch of null values for the item being checked. The test in
> question uses the OGR driver. Here's a quick summary:
> 
> Master:
> 
> -          Using OGR driver gets expression WHERE island_e like "%" and
> returns 3 features, ignoring nulls
> 
> -          Using shapefile driver gets expression "[island_e]" ~ ".*" and
> returns all features
> 
> RFC 91:
> 
> -          Using OGR driver gets expression  "[island_e]" ~ ".*" and
> returns all features
> 
> -          Using shapefile driver gets expression "[island_e]" ~ ".*" and
> returns all features
> 
> This change is because RFC 91 translation runs through the MapServer
> expression syntax and the OGR driver can handle both cases. However,
> that's not the problem since you shouldn't see the difference in master
> either - a straight shapefile fails. I'm guessing that way down in the
> shapefile driver nulls in the DBF are handled as empty string which
> technically match the "0 or more character" pattern. Any ideas on how to
> deal with something like this? 

In OGR, empty strings in .DBF are consider as NULL values, and not empty 
strings. I'm not sure this is a universal choice, because DBF has no proper 
way of specifying the NULL concept.
And I don't think there's this concept of NULL currently in MapServer 
attributes (the lack of typing is also quite limiting sometimes). The start 
would be to change msDBFReadAttribute() to return NULL if DBFIsValueNULL(). 
But that would likely cause many problems in the rest of the code base.... 
Or a more restricted change when a LIKE is evaluated to consider that empty 
string is NULL and then evaluate it to FALSE.

> Changing the regex to ".+" makes the test
> pass but I don't think that's the correct solution.
> 
> Steve
> 
> StEVE LIME  | DATA & Applications MANAGER
> MN.IT Services @ MnDNR
> 651-259-5473 (w)  |  651-297-4946 (f) | 
> steve.lime at state.mn.us<mailto:Your.name at state.mn.us>
> 
> [cid:image003.jpg at 01CFC051.43750460]<http://www.mn.gov/oet>
> 
> Information Technology for Minnesota Government   |  
> mn.gov/oet<http://www.mn.gov/oet>

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