def destroy_key attribute, key
      raise "invalid attribute #{attribute}" unless self.class.column_names.include?(attribute.to_s)
      new_value = send(attribute)
      new_value.delete(key.to_s)
      send("#{attribute}=", new_value)
      self
    end
def destroy_key attribute, key
      raise "invalid attribute #{attribute}" unless self.class.column_names.include?(attribute.to_s)
      new_value = send(attribute)
      new_value.delete(key.to_s)
      send("#{attribute}=", new_value)
      self
    end
Deletes a key in a record. E.g.
   witt = Person.find_by_name("Ludwig Wittgenstein")
   witt.destroy_key(:info, :father)
 It does not save the record, so you'll have to do it.