extract_attribute

# File activerecord/lib/active_record/relation/where_clause.rb, line 136
        def extract_attribute(node)
          attr_node = nil

          valid_attrs = Arel.fetch_attribute(node) do |attr|
            !attr_node || attr_node == attr # all attr nodes should be the same
          ensure
            attr_node = attr
          end
          return unless valid_attrs # all nested nodes should yield an attribute

          attr_node
        end