Use delete_all to remove impressions on a model

lib/impressionist/is_impressionable.rb

@@ -15,7 +15,7 @@ module Impressionist
       def define_association
         has_many(:impressions,
         :as => :impressionable,
-        :dependent => :destroy)
+        :dependent => :delete_all)
       end
     end
 

lib/impressionist/models/mongo_mapper/impressionist/impressionable.rb

@@ -9,7 +9,7 @@ module Impressionist
         def is_impressionable(options={})
           many(:impressions,
           :as => :impressionable,
-          :dependent => :destroy)
+          :dependent => :delete_all)
 
           @impressionist_cache_options = options
         end

tests/test_app/spec/models/model_spec.rb

@@ -57,14 +57,14 @@ describe Impression do
     @article.impressionist_count(:filter=>:session_hash).should eq 7
   end
 
-  # tests :dependent => :destroy
+  # tests :dependent => :delete_all
   it "should delete impressions on deletion of impressionable" do
     #impressions_count = Impression.all.size
     a = Article.create
     i = a.impressions.create
     a.destroy
     a.destroyed?.should be_true
-    i.destroyed?.should be_true
+    Impression.exists?(i.id).should be_false
   end
 
 end