Ruby / Rails metaprogramming: generating helper methods on the fly

Question

I am trying to generate some count methods dynamically for a given array of model names that I can then use in a view/helper:

  # create dynamic count methods for each model we want                   
  ['model', 'other_model', 'next_model'].each do |name|
     class_eval{
       "def total_#{name.underscore}s_count
          total_#{name.underscore}s_count ||= #{name.camelcase}.all.count
        end"
      }
  end

However, I have a few questions:

Where should this code go if I want to be able to call these methods in a view?
What class would these methods be added to? For instance, how would I go about calling them since I'm not sure if they belong to the User, etc. class since they are for a bunch of models.
Is there a better way of doing this?

What is the advantage of total_model_count over Model.count? — Victor Moroz
– Victor Moroz, Commented Jun 8, 2011 at 15:00

Wizard of Ogz · Accepted Answer · 2011-06-08 13:57:17Z

3

You should use a mixin and include it in the relevant model classes. http://juixe.com/techknow/index.php/2006/06/15/mixins-in-ruby/

The methods will be available on the model instances in your views.

answered Jun 8, 2011 at 13:57

Wizard of Ogz

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coreyward · Accepted Answer · 2011-06-08 17:20:39Z

1

The problem you're trying to solve (keeping your views from hitting model methods) isn't solved by delegating the same logic to a view helper. You should be doing this in your controllers if you want to stick to the MVC convention of keeping your views from triggering SQL queries.

def index
  models = Foo, Bar, Bat
  @counts = models.inject({}) do |result, model|
    result[model.name.downcase.to_sym] = model.count
    result
  end
end

You then have a nice hash of the counts of each of the models passed:

@counts #=> { :foo => 3, :bar => 59, :bat => 42 }

answered Jun 8, 2011 at 17:20

coreyward

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