Question

I’m writing my first rails plugin and could use a little help. In a very simplified way, I’d like to do allow the developer to specify a value which I can count through a rake task. I’m thinking of something like this…

class User < ActiveRecord::Base
    monitor "Users", count
    monitor "Active Users", count("activated_at != NULL")
end

1. I guess monitor needs to be a class method of ActiveRecord::Base but how/where do I specify it in my plugin?
2. The argument to the monitor function shouldn’t be the value but a block of code to execute. I’m not quite sure of the best way to specify this and keep the syntax simple. Perhaps it’ll have to be monitor "Active Users", {count "activated_at != NULL"}?
3. I’d prefer if the developer didn’t have to specify User.count, just count, i.e. it would pick up the Class automatically (and the blocks will be called on the class not the instance). If this isn’t possible, I guess there’s no reason to put the monitor statements into the model (see #5).
4. The actual counting of these values (i.e., execution of the blocks) will be done by a rake task offline. What should the monitor function do to make these blocks available to the rake task? Store them in a class variable?
5. Perhaps the monitor statements don’t need to be specified in the model at all. Maybe it clutters it up so I’d welcome any alternative places to put them.

I’m just sketching out my ideas at the moment and trying to figure out what is/isn’t possible in Ruby. Any help appreciated.

Update: I’ll try to be clearer on the plugin’s purpose. I want the developer to be able to define metrics which should be monitored by the rake task. The rake task will iterate over those metrics and write the values to a file (I’ve simplified this a bit). The rake task will be very simple, something like rake monitors:update (i.e., no params required)

Answer 1

Thanks for all your help, however I went with a different approach (extracted below).

Instead of specifying the attributes in the models, I used an approach seen in the whenever gem. I placed a ruby file “dashboard.rb” in my config directory:

dashboard "Users", User.count
dashboard "Activated Users", User.count('activated_at')

My lib consists of two functions:

  def self.dashboard(name, attribute)
      puts "** dailydashboard: #{name} = #{attribute.to_s}"
  end

  def self.update(file)
    eval File.read(file)
  end

Basically, my rake task calls update, which loads dashboard.rb and evaluates it and repeatedly calls the dashboard function, which outputs this:

** dailydashboard: Users = 2
** dailydashboard: Activated Users = 1

Sorry for going around the houses a little bit. For background/offline things this seems like a very simple approach and does what I need. Thanks for your help though!