How do I convert a Ruby class name to a underscore-delimited symbol?

Question

How can I programmatically turn a class name, FooBar, into a symbol, :foo_bar? e.g. something like this, but that handles camel case properly?

FooBar.to_s.downcase.to_sym 

Answer 1

Rails comes with a method called underscore that will allow you to transform CamelCased strings into underscore_separated strings. So you might be able to do this:

FooBar.name.underscore.to_sym 

But you will have to install ActiveSupport just to do that, as ipsum says.

If you don't want to install ActiveSupport just for that, you can monkey-patch underscore into String yourself (the underscore function is defined in ActiveSupport::Inflector):

class String   def underscore     word = self.dup     word.gsub!(/::/, '/')     word.gsub!(/([A-Z]+)([A-Z][a-z])/,'\1_\2')     word.gsub!(/([a-z\d])([A-Z])/,'\1_\2')     word.tr!("-", "_")     word.downcase!     word   end end 

Answer 2

Rails 4 .model_name

In Rails 4, it returns an ActiveModel::Name object which contains many useful more "semantic" attributes such as:

FooBar.model_name.param_key #=> "foo_bar"  FooBar.model_name.route_key #=> "foo_bars"  FooBar.model_name.human #=> "Foo bar" 

So you should use one of those if they match your desired meaning, which is likely the case. Advantages:

• easier to understand your code
• your app will still work even in the (unlikely) event that Rails decides to change a naming convention.

BTW, human has the advantage of being I18N aware.