I am trying to use a module to define a common interface between several ActiveRecord model classes, but I am having trouble setting the instance variable in the mixin functions. For example, I have a mixin, module Photogenic def self.included( other_mod ) other_mod.module_eval do has_many :images, :as => :photogenic, :dependent => :destroy do def showpictures @user = User.find(params[:id]) @images = @user.images end end end end end If I put the function show pictures in the action controller, it works fine, but if I move it to the module, the instance variable @user and @images is nil when I try to call it in the .rhtml file. Does anyone know why this is? Did I just implement the code incorrectly or am I using mixins incorrectly. Do I have access to params[:id] in the mixin? I briefly read that you can only use mixins to define non-action methods. Does anyone know if this is true and why that would be the case? Anyway, I would greatly appreciate any advice. I found examples of people using mixins to add methods to Active Record classes, but none of these functions tried to set instance variables or acted as action methods, so I feel I am incorrectly using the mixin. Thanks, Chris
on 2007-05-15 18:26
on 2007-05-15 18:32
I don't know enough Ruby to tell you about mixins, but here are two Rails-y thoughts: 1. You can put methods that you want in all controllers in controllers/application.rb. 2. If you want those methods to be available to your views, use helper_method :showpictures in the same file.
on 2007-05-15 20:24
Thanks for the advice. I did consider both options you provided, but because of my situation, it seems like a mixin or something similar to it would work best for my case...though a mixin may not work at all. I realize now that I did not really describe my situation well. Hopefully I can clarify what I am trying to do without making the post too long. The reason I do not want to put it in the application.rb is that only a few of my classes would have pictures, so I only want to give photogenic functions to those specific classes. I am basically trying to create a inheritance structure where three of my classes[ User, Court, and Character ] have images and so have the photogenic mixin. My situation is actually very similar to the case described in the website below, except I want to put action methods in the mixin. excerpt from: http://johnwilger.com/2006/10/defining-interfaces-... #mixin module Commentable has_many :comments, :as => :commentable do def approved find( :all, :conditions => ['approved = ?', true ] ) end end end #classes the include mixin class BlogEntry < ActiveRecord::Base include Commentable end class ResearchArticle < ActiveRecord::Base include Commentable end class Photograph < ActiveRecord::Base include Commentable end #class I want to associate to the above classes class Comment < ActiveRecord::Base belongs_to :commentable, :polymorphic => true end I also looked into putting these functions in a helper. In my case I also want to add methods that edit, add, and remove images, which may not be a good idea to put in the helper functions which are meant more for creating html. I was thinking about it, and if I can't use mixins, I will most likely take your advice and put the functions more related to the views in the helper functions. When I look into the details of using the mixin to achieve a pseudo inheritance where objects have associations, I can see many problems that can arise in addition to not being able to set the instance variables. I am guessing I will not be able to use a mixin for this case though it would really clean up my code if I could. Even though I may not be able to use a mixin, I am trying to figure out how mixins can be used for other siutations. >From the results I have seen so far, it appears mixin functions cannot change instance variables from the class they are includes them. If that is true, does that mean mixins can really only be used to calculate and return a value or object. Anyway, thanks again for the help. Any information on how mixins can be used properly or any suggestions on alternative solutions to my problems will really help me solve this problem and help me learn more about Rails. This is actually the first time I've tried dealing with the modules and mixins, so I am trying to learn as much as possible and expect this first time to be slow. Chris
on 2007-05-15 23:09
> The reason I do not want to put it in the application.rb is that only > a few of my classes would have pictures, so I only want to give > photogenic functions to those specific classes. I am basically trying > to create a inheritance structure where three of my classes[ User, > Court, and Character ] have images and so have the photogenic mixin. Why not just create an inheritance structure? RoR does support "single- table-inheritance." Just a thought....
on 2007-05-16 20:17
On 5/15/07, email@example.com <firstname.lastname@example.org> wrote: > From the results I have seen so far, it appears mixin functions cannot > change instance variables from the class they are includes them. methods from a mixin can change instance variables. What is leading you to believe that they can't?