It's a pretty simple mistake, but it's confused by your unconventional
association. Normally, you would assign to the association name plus
'_id', but that doesn't match the class. And just like the error
says, you can't assign a string (the Country object's ID) to the
association (because it wants a Country object). Try a select on
country_id instead of origin_country or origin_country_id.
By the way, I prefer to fully qualify any association that doesn't use
belongs_to :origin_country, :class_name => 'Country', :foreign_key
Otherwise, it can be confusing to know whether the foreign key depends
on the association name or class name (and I believe it has switched
or will switch or something, but I could be wrong about that).