Rails - finding the right place for common code

Question

I have got myself quite befuddled. I have some code which takes some images, combines them and then spits out the combined image in .png format.

Originally this code was a method for a model - with the model's associations indicating which images to use. Thus:

class Component < Refinery::Core::BaseModel  
    drawing_accessor :drawing
  . . .
end

class Photo < Refinery::Core::BaseModel
  has_and_belongs_to_many :components
  has_many :drawings, :through=>:components

  def diagram
    . . . .
    Base64.encode64(png.to_blob)    #spit out the png as a base64 encoded string
  end
end

and in a view I could write

  <img src="data:image/png;base64,<%=@photo.diagram%>"

Now, I need to do the same combining of images, but directly from a list of component ids. As the component ids haven't been saved to a photo (and may not be) I need to move this code out of the photo model.

I want to able to call the same drawing code with a parameter that is a list (array or collection) of component ids, regardless of where they come from.

It seems that as the diagram comes from a set of components, it should belong with the components...somewhere.

In my various tries I end up with undefined method for an ActiveRecord::Relation, or for an Array.

Can you help clarify my thoughts about where this code belongs and how to call it?

thanks

Answer 1

Well, the Power of Posting has hit again.

I put in a new route for the components collection:

  resources :components do
    collection do
      get :draw
    end
  end

with a matching definition in the controller

def draw                 
  send_data Component.construct(params[:list],params[:width], params[:height]), :type => 'image/png', :disposition => 'inline'
end  

and a method on the model to draw the components

  def self.construct(component_list, width, height)
  . . . 
    Base64.encode64(png.to_blob)    #spit out the png as a base64 encoded string
  end 

The Photo model includes a method which pulls together the component list then call construct:

  def diagram
    component_list = []
    # construct the list of ids in the right order (bottom to top, or base to capital)
    ....
    Component.construct(component_list, self.image.width, self.image.height)
  end

And from javascript I can call

var component_list = $("input:checked").map(function(){return this.value}).get();
. . . 
$.get(url,{list:component_list, width:width, height:height}, function(data) {
  $('img.drawing').attr("src","data:image/png;base64," + data);
})

I still have doubts about including the methods in the models and not somewhere in a view or view helper, but this does seem to work!