Question

I’m writing a Ruby module to provide automatic markdown generation on blog posts etc.

The code so far looks like this:

class Post < ActiveRecord::Base
  contains_markdown
end

module MarkdownMixin
  def contains_markdown
    # HELP! :)
  end
end

ActiveRecord::Base.send :extend, MarkdownMixin

That code seems to be working (i.e. my unit tests don’t throw any ‘not defined’ errors etc.). The Post table contains an input and formatted column.

Where I’ve written # HELP I want to inject code to the Post model so that whenever a change is made to input, formatted is recalculated (using a Markdown engine). Something like (pseudo-code):

def on_input_changed
  @formatted = Redcarpet.new(@input).to_html
end

Now I’m still really getting my head around Ruby mixins so my brain’s slightly spinning trying to work out what incantation to call in my module.

So far I’ve found this article quite useful, but can’t work out how to apply it here.

Answer 1

I think the easiest way would be to use a before_save where you make the transformation.

def contains_markdown
  before_save do |record|
    record.formatted = Redcarpet.new(record.input).to_html
  end
end