How can I make named_scope in Rails return one value instead of an array?

In this case I'd create a class method

def self.from_id(id)  self.find(id).firstend

Another example:

class Invoice  def self.number    self.find(:first,       :select => "max(number) As last, max(number)+1 As next",       :conditions => "type = 'SalesOrder'")  endend

Methods like this its better then named_scope. You can call Invoice.number.next, better than named_scope return Invoice.number[0].next.

As Damien mentions, using a custom scope just to look up by ID isn't advisable. But to answer your question:

Finding records with named_scope will always return an ActiveRecord::NamedScope::Scope object, which behaves like an array. If there is just a single record returned by your query, you can use the first method to get the ActiveRecord object directly, like this:

event = Event.from_id(id).firstevent.name # will work as you expect

There's no need to use a scope here. You could just do Event.find_by_id id.
The difference between find and find_by_id is that the first one will raise an ActiveRecordNotFoundException if the record does not exist. The second one will just return nil.

Writing a scope to get the record by it's id is a very bad id as it is something which is already provided natively by rails.