Handling ActiveRecord::RecordNotFound errors

Can anyone explain why an ActiveRecord::RecordNotFound error is only thrown on a regular id-based find, such as Product.find(123)? For example, if you're using a dynamically generated attribute find method, such as Product.find_by_name('asdfd'), and no results match, it just returns nil, and no error is thrown.

That's expected. The reasoning being that if you look up a record by id then you're expecting the record to be there, so if it's missing that's an exceptional condition. On the other hand, with a find :first (which is what find_by_xxx ends up doing) or find :all, you don't have that expectation. For example the user has decided to search for records matching a set of criteria or something along those lines and so there not being any records to return is a perfectly normal thing. How you handle this is completely application dependant (it might be as simple as rendering 'No results found')