Matching empty strings

[ashh87]

Updating openstreetmap-carto (gravitystorm/openstreetmap-carto#517 for details) I tried to filter data by "[access = '']". openstreetmap-carto already contains filters for "[access != '']" and these work fine. I can't get "[access = '']" to work though. I have a postgis setup, with a node that I want to be rendered, it doesn't have an 'access' tag, which is what I thought the rule I am trying should match (as the value for the access column in the relevant database row is blank) - it doesn't render the node with this rule. It doesn't render it when I change to "[access != '']", but that is expected!

Am I taking the wrong approach to this filter, or trying to match an empty(/null) string incorrectly or is this a bug? How does this affect the OSM website (mapnik?) if it is a bug? NB, as mentioned on the linked pull request, doing a regex for a blank string seems to allow the node to render correctly, but I didn't have time to double check my regex was correct :)

[springmeyer]

Try "[access = null]". The "[access != '']" is a hack for old Mapnik versions (before v2.2.0) which did not support filtering on nulls. Now that "[access != null]" and "[access = null]" work you should avoid "[access != '']". It is only there now as a back compatibility shim.

On May 10, 2014, at 7:40 AM, ashh87 notifications@github.com wrote:

Updating openstreetmap-carto (gravitystorm/openstreetmap-carto#517 for details) I tried to filter data by "[access = '']". openstreetmap-carto already contains filters for "[access != '']" and these work fine. I can't get "[access = '']" to work though. I have a postgis setup, with a node that I want to be rendered, it doesn't have an 'access' tag, which is what I thought the rule I am trying should match (as the value for the access column in the relevant database row is blank) - it doesn't render the node with this rule. It doesn't render it when I change to "[access != '']", but that is expected!

Am I taking the wrong approach to this filter, or trying to match an empty(/null) string incorrectly or is this a bug? How does this affect the OSM website (mapnik?) if it is a bug? NB, as mentioned on the linked pull request, doing a regex for a blank string seems to allow the node to render correctly, but I didn't have time to double check my regex was correct :)

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[ashh87]

perfect, thank you ! :)