From 34ca0b6362836984fafeac0dd73ae8cb3ad8aec2 Mon Sep 17 00:00:00 2001
From: Norman Clarke <norman@njclarke.com>
Date: Fri, 11 Nov 2011 11:44:12 -0300
Subject: [PATCH] Attempted fix for concurrency issue.

https://github.com/norman/friendly_id/issues/180
---
 lib/friendly_id/history.rb | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/lib/friendly_id/history.rb b/lib/friendly_id/history.rb
index 6039b7c15..49d36a8d2 100644
--- a/lib/friendly_id/history.rb
+++ b/lib/friendly_id/history.rb
@@ -75,8 +75,14 @@ def self.included(model_class)
     def build_slug
       return unless should_generate_new_friendly_id?
       # Allow reversion back to a previously used slug
-      slugs.where(:slug => friendly_id).delete_all
-      slugs.build :slug => friendly_id
+      Slug.transaction do
+        select = slugs.where(:slug => friendly_id)
+        unless Slug.connection.adapter_name =~ /sqlite/i
+          Slug.connection.execute "#{select.to_sql} FOR UPDATE"
+        end
+        select.delete_all
+        slugs.build :slug => friendly_id
+      end
     end
 
     # Adds a finder that explictly uses slugs from the slug table.