@resource =Resource.find(params[:id], :include =>[:projects, :trainings]
As long as your associations are set in the models, this will work.
class Resource < ActiveRecord::base has_many :trainings
has_many :projects
end
That will work.
Rails has an api at http://api.rubyonrails.com where this is all documented. You should make sure to give that a look if you have additional questions.