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

README.rdoc

@@ -178,6 +178,21 @@ If you want to customize the loading behavior on certain actions, you can do so
 Here the @book instance variable is already set so it will not be loaded again for that action. This works for nested resources as well.
 
 
+== Fetching Records
+
+Sometimes you need to restrict which records are returned from the database based on what the user is able to access. This can be done with the +can+ method on any Active Record model. Simply pass it the current ability and an action.
+
+  @articles = Article.can(current_ability, :read)
+
+The action defaults to :read so that can optionally be left out.
+
+  @articles = Article.can(current_ability)
+
+Here only the records which the user can read will be returned. This is an Active Record scope so other scopes and pagination can be chained onto it.
+
+Note: This does not work for abilities which were defined by a block because the conditions hash can not be determined from them. Instead an exception will be raised.
+
+
 == Assumptions & Configuring
 
 CanCan makes two assumptions about your application.
@@ -205,6 +220,12 @@ It is very easy to test the Ability model since you can call "can?" directly on
     assert ability.cannot?(:destroy, Project.new)
   end
 
+A matcher called +be_able_to+ is provided for testing abilities in RSpec.
+
+  require "cancan/matchers"
+  # ...
+  ability.should be_able_to(:destroy, Project.new)
+
 
 == Special Thanks
 

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
     

spec/cancan/active_record_additions_spec.rb

@@ -3,7 +3,7 @@ require "spec_helper"
 describe CanCan::ActiveRecordAdditions do
   before(:each) do
     @model_class = Class.new
-    stub(@model_class).where { :where_stub }
+    stub(@model_class).scoped { :scoped_stub }
     @model_class.send(:include, CanCan::ActiveRecordAdditions)
     @ability = Object.new
     @ability.extend(CanCan::Ability)
@@ -19,4 +19,10 @@ describe CanCan::ActiveRecordAdditions do
     stub(@model_class).where(:foo => 1) { :found_records }
     @model_class.can(@ability, :read).should == :found_records
   end
+  
+  it "should default to :read ability and use scoped when where isn't available" do
+    @ability.can :read, @model_class, :foo => 1
+    stub(@model_class).scoped(:conditions => {:foo => 1}) { :found_records }
+    @model_class.can(@ability).should == :found_records
+  end
 end