Rails 3 direct column reader
Whilst trying to get my head around arel and it's relationship to ActiveRecord in rails 3, I've updated the simple ColumnReader class I introduced last year. It lets you read the (correctly cast) column values for an ActiveRecord class, without the overhead of instantiating each object.
Here's the updated code:
module ColumnReader
def column_reader(column_name, options = {})
name = options.delete(:as) || column_name.to_s.pluralize
column = columns_hash[column_name.to_s]
self.module_eval %{
def self.#{name}
query = scoped.arel.project(arel_table[:#{column_name}])
connection.select_all(query.to_sql).collect do |value|
v = value.values.first
#{column.type_cast_code('v')}
end
end
}
end
ActiveRecord::Base.extend(self)
end
The code isn't that different, though using scoped over construct_finder_sql feels a lot nicer. If you've got suggestions for improvement gist away.
Usage is similar to before, only using the new rails 3 syntax:
class Animal < ActiveRecord::Base
column_reader 'id'
column_reader 'name'
named_scope :dangerous, :conditions => {:carnivorous => true}
end
Animal.names
#=> ['Lion', 'Tiger', 'Zebra', 'Gazelle']
Animal.limit(1).names
#=> ['Lion'] (Normal finder options supported)
Animal.dangerous.names
#=> ['Lion', 'Tiger'] (Scoping respected)
Animal.ids
#=> [1, 2, 3] (Values cast correctly)
I'm still not entirely convinced of the value of this helper, so if you find a good use tweet me. Enjoy!