MS RFC 9: Item tag for query templates

Author:Steve Lime
Contact:steve.lime at DNR.STATE.MN.US
Version:MapServer 4.10

Description: A the moment processing of attributes exposed via query templates is limited to a couple forms of escaping. This is too limiting. It would be much nicer to be able to apply a format to an attribute (e.g. truncate decimals or add a prefix) or detect when it is NULL or empty and present an alternative representation. This RFC describes a simple scheme to allow for extended processing of attributes before sending to the a users.

This would involve adding a new “item” tag to the template processor.

Files affected

  • maptemplate.c => add tag processor, update query template processor to use tag processor.

Backwards compatibility issues

N/A, new functionality. Existing methods for exposing an attribute (e.g. [attribute name] would continue to function, although we might mark that as deprecated at some point.

Implementation Details

The “item” tag would have the following properties.

  • name: the name of the attribute to be exposed
  • format: a simple string containing the token(s) $value, default format is the result of any processing
  • nullformat: string to return if value is NULL or empty (length=0)
  • uc: convert string to upper case
  • lc: convert string to lower case
  • substr: perform a perl-like substring operation by providing offset, and optionally length (un-implemented as of 3/13/07)
  • commify: add commas to a numeric string (12345 would become 12,345), note, supports only North American notation at the moment
  • escape: what type of escaping to do (default is html), permissible values would be html, url, none
  • precision: number of decimals to retain after the decimal point
  • pattern: regular expression that must validate (against the column value) to process the tag

We could add simple case statement support at a later date but the above would more than meet my needs at the moment.


Display no decimal places, and commify:

[item name=foo commity=true precision=0] - 12345.6789 output as 12,345

Conditional display an item if its value contains ‘bar’:

[item name=foo pattern=bar]

Escape a value for inclusion in a URL, and convert to upper case:

[item name=foo uc=true escape=url] - “hello world” output as “HELLO%20WORLD”

Apply a custom format to an item, and display a message if the item is empty:

[item name=foo format=”foo=$value” nullformat=”foo is not found”]


Item tags are processed after other column tags (e.g. [foo]) so you can include substitution strings within the item tag itself.

Bug ID


Voting history

+1: Lime, Morissette, Butler +0: Gillies, Warmerdam