grimen · September 13, 2009 14:48 · Sep 3, 2009
diff --git a/gistfile1.txt b/gistfile1.txt
@@ -0,0 +1,32 @@
+One other cause is your :dependent callbacks.
+
+    class Blog < AR::Base
+      has_many :posts, :dependent => :destroy
+    end
+
+This will iterate through every post and call #destroy on it.  Use :delete_all if you want to just issue a single delete query.  HOWEVER, this won't hit your destroy callbacks on Post.
+
+    class Blog < AR::Base
+      has_many :posts
+      after_destroy :purge_posts
+
+    private
+      def purge_posts
+        # one step better, it only loads a page of posts and hits every post destroy callback
+        posts.paginated_each { |p| p.destroy }
+
+        # even better, but not very dry
+        # cheating a bit w/ a denormalized Comment table,
+        # but this is a blog comment and i'm pressed for time :)
+        Comment.delete_all :blog_id => id
+        Post.delete_all :blog_id => id
+    end
+
+The solution I've been using for this is WillPaginate.
+
+    # instantiate only 30 users at a time
+    User.paginated_each do |user|
+      user.do_some_stuff!
+    end
+
+Keep in mind that using Sequel or DM won't make you immune to all these (though DM has a nice identity map that helps in a lot of cases).