Relationship puzzle

[eluser]Unknown[/eluser]
Thanks for the input.
It turns out I was suffering from a classic programmer's error - tunnel vision, focussing on the datamapper usage only- and hadn't checked the database table (written by somebody else) so, looking for 'name' as a field was plain stupid as the field was called 'common_name' (doh). In fact my original script did work!

However, your second suggestion led me to investigate the 'where_related_{category}' stuff in the documentation, and I realised there was a whole area of datamapper that I hadn't gone into. I had found the raw documentation a bit obtuse , but now with a practical example of my own, it has started to make some sense.