Comparison <=> operator on string attributes of ActiveRecord objects

Here’s a little gotcha for you which caught me out by surprise, obvious when you think about it, but irritating if you miss it: the ruby String comparison operator does case-sensitive comparisons.

# Good:
['C', 'b', 'A', 'D'].sort #=> ['A', 'b', 'C', 'D']

# Bad (what <=> gives you out the box):
['C', 'b', 'A', 'D'].sort #=> ['A', 'C', 'D', 'b']

For a nice efficient implementation of a AR model comparitor use the String#casecmp method for a case-insensitive comparison:

class MyObject
  def <=>(other)
    self.my_attribute.casecmp(other.my_attribute)
  end
end