You could do this (but maybe ask yourself why):

user.attributes.key(user.first_name) 

...will return "first_name" as a String.

(Edited to reflect better answer by MrTheWalrus below. Please upvote his comment rather than this post).

You could do this (but maybe ask yourself why):

user.attributes.key(user.first_name) 

...will return "first_name" as a String.

You could do this (but maybe ask yourself why):

user.attributes.select {|_,v| v == user.first_name }.keys.first 

... which will return "first_name" as a String.

Are you looking for some way of determining which attribute matches a given input?

class User < ActiveRecord::Base #... def attribute_name_by_value(value) attributes.each {|k,v| return k if v == value } nil end end 

Then user.attribute_name_by_value("[email protected]") would return "email".

You could do this (but maybe ask yourself why):

user.attributes.key(user.first_name) 

...will return "first_name" as a String.

(Edited to reflect better answer by MrTheWalrus below. Please upvote his comment rather than this post).