Difference between :collection and :member in Rails 2.0

11 Aug 2008

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In getting up to speed with the new bells and whistles in Rails 2.0s RESTful routing capabilities I ran into something that puzzled me.  Of the options for a resource defined among your routes there were two similar pieces that, for one reason or another, I could just not find a solid and bulletproof explanation for – :collection and :member.  The :member part of it I got pretty easily for some reason, because its description is inherent in its own name … “a member among the default restful actions”.  The :collection part?  Notsomuch.  After some digging in the Rails mailing list I ran into a great, and worthy, explanation for this knucklehead by a contributer named “deegee”:

For example, with map.resources :reviews, if you want to add a method ‘delete_all’ that deletes all reviews at once. You may want to call that with ‘/reviews/delete_all’ and method PUT (never use GET to delete something). This method is acting on all resources (a collection), so the route should be:

map.resources :reviews, :collection => { :delete_all => :put }

If you want to have a custom action acting on a specific resource, e.g. ‘/reviews/3/give_rating’, then your action is on a member and the route would be

map.resources :reviews, :member => { :give_rating => :put }

So that’s it! They’re the same other than :member working on a single resource, while :collection works on multiple.  DONE!