Once we were only wading to the knee in Rails documentation. Now that the belt buckle is submerged, we all take turns excavating.

ActiveRecord::Base#constrain

I’m in the controller. I want to limit a view to a subset.

  Article.constrain(:conditions => "blog_id = 1") do
    Article.find(1) # => SELECT * from articles WHERE blog_id = 1 AND id = 1
  end

In combo with permissions, this can be great. Because constrain can take nil.

  constraints = nil
  unless @user.sees_all?
    constraints = {:conditions => ['user_id = ?', @user.id]}
  end

Has anyone coupled this with destroy to nuke a chain of associated rows?

Update: From the comments, we learn that constrain is behind the scoped database calls.

Receiving Through ActionMailer

I want messsages to a certain e-mail address to travel through Rails. The wiki has a very thorough discussion on the topic, including many setup options.

Specifically, here’s a way to handle bounces. In other words, if an e-mail bounces to an address that’s signed up for a login, you could flag the account, giving the user a better reason why their account isn’t active.

  class Inbox < ActionMailer::Base

    def receive(bounce)
      from = bounce.from.first

      if from =~ /MAILER-DAEMON/
        bounce.each_part do |part|
          if part.content_type == "text/rfc822-headers" 
            email = TMail::Mail.parse( part.body )
            user = User.find_by_email( email.to.first )
            user.update_attributes :disabled => true
            return
          end
        end
      end

    end

  end

It’d be good to have TMail in the API docs. But the above should give you an idea of how to parse attachments which contain email headers. And how to cycle attachments.

Forming XHTML from User Input

We’ve talked about this before, but I swear this is the shortest recipe and most cooperative. Assume you have incoming blog content HTML contained in the html_content accessor. Also, require 'htree' in your config/environment.rb.

 def xhtml_content
   HTree.parse( html_content ).display_xml( '' )
 end