Access to a non ActiveRecord attribute in before_save callback

Question

In my view, I use a <%= f.text_field :latlon %> to edit the latlon attribute (not an ActiveRecord column). When saving, I want to parse latlong and split it into lat and lon in a before_save callback.

I don't know how to access to the params of the latlon variable inside the callback. I have tried self.latlong but that calls the same attr_reader as the lat and lon attributes.

I know I can do this in the controller but, this is model logic, no?

#app/models/bla.rb
class Bla < ActiveRecord::Base
  attr_accessible :name, :lat, :lon, :latlon #but latlon is not an ActiveRecord Attribute

  before_save :foo

  def latlon
    "#{lat}, #{lon}"
  end

  attr_writer latlon

  private

  def foo
    self.lat = # regex that parse latlon
    self.lon = # regex that pase coors
  end

end

Yes, this is model logic, but you'll need to pass the right value from the controller. — Tom Harrison, Nov 30 '12 at 21:34
Its not exactly an error, the problem is that when I call the latlon method (attr_reader) it will return me "#{lat}, #{lon}" , instead of its real value — eveevans, Nov 30 '12 at 21:37
@TomHarrisonJr , yes, I pass the right value via form from the view. I mean, If I call latlong without define the latlon method, I will return the right value, but when I enter to the view I will not see the latlon value, — eveevans, Nov 30 '12 at 21:41
If the view references an instance of the Bla model, @bla.latlon should contain the current values of `lat` and `lon` formatted correctly. You might have to handle nil cases or something but that should work fine. And going the other direction, the form should have `params => {:bla => {:latlon => "12.3456, 78.9012", ...}}` which you should be able to save (see Xathras's and my answer). — Tom Harrison, Nov 30 '12 at 21:46

score 3 · Answer 1 · answered Nov 30 '12 at 21:39

3

You can override the assignment method to do what you're describing. This has the bonus of being faster/easier to unit test.

def latlon=(new_value)
  # do work to split and assign
end

answered Nov 30 '12 at 21:39

Andrew Kothmann

607
3
4

score 1 · Accepted Answer · answered Nov 30 '12 at 21:40

I would think that you might replace attr_writer latlon with

def latlon=(latlon)
  self.lat = # regex that parses lat from latlon
  self.lon = # regex that parses lon from latlon
end

And maybe don't make :lat and :lon part of attr_accessible since they will never be mass-assigned, i.e. from the params array. params passed from the controller will contain the latlon value (formatted correctly).

I don't think you need a before_save in this case.

yeah, this is the same as what @Xathras suggested :-) – Tom Harrison Nov 30 '12 at 21:41 — Tom Harrison, Nov 30 '12 at 21:41

score 0 · Answer 3 · answered Nov 30 '12 at 21:28

0

The model should have access to the instance variable @latlon that you can use, right?

answered Nov 30 '12 at 21:28

Jakob W

3,347
19
27

yes, but It will call to my latlon method (attr_reader) that will be "#{lat}, #{lon}" , instead of its real value – eveevans Nov 30 '12 at 21:35
1

Take a look at http://stackoverflow.com/questions/5046831/why-use-rubys-attr-accessor-attr-reader-and-attr-writer – John Naegle Nov 30 '12 at 21:38

Access to a non ActiveRecord attribute in before_save callback

3 Answers3