default ActiveRecordAdditions#can method action to :read and use 'scoped' if 'where' is not available

lib/cancan/ability.rb

@@ -191,9 +191,7 @@ module CanCan
     #   can :read, Article, :visible => true
     #   conditions :read, Article # returns { :visible => true }
     # 
-    # For example, you can use this in Active Record find conditions to only fetch articles the user has permission to read.
-    # 
-    #   Article.where(current_ability.conditions(:read, Article))
+    # Normally you will not call this method directly, but instead go through ActiveRecordAdditions#can method.
     # 
     # If the ability is not defined then false is returned so be sure to take that into consideration.
     # If the ability is defined using a block then this will raise an exception since a hash of conditions cannot be

lib/cancan/active_record_additions.rb

@@ -2,8 +2,30 @@ module CanCan
   # This module is automatically included into all Active Record.
   module ActiveRecordAdditions
     module ClassMethods
-      def can(ability, action)
-        where(ability.conditions(action, self) || {:id => nil})
+      # Returns a scope which fetches only the records that the passed ability
+      # can perform a given action on. The action defaults to :read. This
+      # is usually called from a controller and passed the +current_ability+.
+      #
+      #   @articles = Article.can(current_ability)
+      # 
+      # Here only the articles which the user is able to read will be returned.
+      # If the user does not have permission to read any articles then an empty
+      # result is returned. Since this is a scope it can be combined with any
+      # other scopes or pagination.
+      # 
+      # An alternative action can optionally be passed as a second argument.
+      # 
+      #   @articles = Article.can(current_ability, :update)
+      # 
+      # Here only the articles which the user can update are returned. This
+      # internally uses Ability#conditions method, see that for more information.
+      def can(ability, action = :read)
+        conditions = ability.conditions(action, self) || {:id => nil}
+        if respond_to? :where
+          where(conditions)
+        else
+          scoped(:conditions => conditions)
+        end
       end
     end