It appears the default sort direction is always sent to the query,
even if a different column is clicked to sort.
add_to_sortable_columns('search', :model => Status, :field => 'name',
:sort_direction => :desc)
that results in:
ORDER BY statuses.name DESC,directories.updated_at DESC
Being sent everytime, even on the sorting of a different field altogether.
The default sort order is:
:order => sortable_order('search',
:model => Directory,
:field => 'updated_at',
:sort_direction => :desc
In other words, no matter what the default sort order is always sent
to the query, and in an un-observable order.