How to determine the parent of an arbitrary topic?

I would like to extract the parent topic of an arbitrary topic, and the solutions I'm coming up with are really grotty. I'm creating a form which allows reparenting of a topic within a subset of existing topics, so need to put the topic name in a select list. The form will be %INCLUDE%d.

Initially, I thought %META% would do the trick, but it doesn't provide a topic parameter, so I can't simply do

%META{ 
    "parent"
    format="$topic"
    topic="%INCLUDINGTOPIC%"
}%

Instead, I've resorted to this monster:

%SEARCH{
    "parent.name"
    type="query"
    topic="%INCLUDINGTOPIC%"
    format="$parent"
    nonoise="on"
}%

which makes me cringe and seems like the proverbial sledge hammer, especially when wrapped in an %IF%:

%IF{ "'%INCLUDINGTOPIC%'/parent.name"
        then="$percntSEARCH{ "parent.name" type="query" topic="%INCLUDINGTOPIC%" format="$parent" nonoise="on"}$percnt" 
        else="No Parent"
}%

(which is further stuck into a default parameter in %FORMELEMENT%).

I must be missing something obvious. If %SEARCH% is the way to go, a nice addition would be a parameter to it to specify a string to return if the search came up empty.

-- DiabJerius - 22 Jan 2010

Well, that last %IF% doesn't work anyway. What I really want to do is this (in pseudo-perl)

if ( defined $topic->parent )
  output( $topic->parent->name )
else
  output ( 'No Parent' )
endif

It's actually trickier, as I really want to output $topic->parent->formfield('Name'), as topic names are autogenerated and a "real" name is stored in the Name form field.

-- DiabJerius - 22 Jan 2010

I know it's no help, but 1.1 introduces the %QUERY macro to address precisely this sort of application. Your solution above is what I would have used pre 1.1.

-- CrawfordCurrie - 18 Mar 2010

See HierarchicalNavigation for a working SEARCH to accomplish this on Foswiki 1.0.9 and earlier.

-- ArthurClemens - 23 Mar 2010