From 66023eccb66f327d174685686f98955030d820f2 Mon Sep 17 00:00:00 2001
From: Prathamesh Sonpatki <csonpatki@gmail.com>
Date: Sat, 16 Jan 2016 13:03:07 +0530
Subject: [PATCH] Fix ActiveRecord::Relation#cache_key for relations with no
 results

- When relations return no result or 0 result then cache_key should
  handle it gracefully instead of blowing up trying to access
  `result[:size]` and `result[:timestamp]`.
- Fixes #23063.
---
 activerecord/lib/active_record/collection_cache_key.rb | 10 ++++++++--
 activerecord/test/cases/collection_cache_key_test.rb   |  5 +++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/activerecord/lib/active_record/collection_cache_key.rb b/activerecord/lib/active_record/collection_cache_key.rb
index b0e555038e..b20df1c232 100644
--- a/activerecord/lib/active_record/collection_cache_key.rb
+++ b/activerecord/lib/active_record/collection_cache_key.rb
@@ -19,8 +19,14 @@ module ActiveRecord
           .unscope(:order)
         result = connection.select_one(query)
 
-        size = result["size"]
-        timestamp = column_type.deserialize(result["timestamp"])
+        if result.blank?
+          size = 0
+          timestamp = nil
+        else
+          size = result["size"]
+          timestamp = column_type.deserialize(result["timestamp"])
+        end
+
       end
 
       if timestamp
diff --git a/activerecord/test/cases/collection_cache_key_test.rb b/activerecord/test/cases/collection_cache_key_test.rb
index 93e7b9cff6..6b34979e4a 100644
--- a/activerecord/test/cases/collection_cache_key_test.rb
+++ b/activerecord/test/cases/collection_cache_key_test.rb
@@ -74,5 +74,10 @@ module ActiveRecord
 
       assert_match(/\Acomments\/query-(\h+)-0\Z/, empty_loaded_collection.cache_key)
     end
+
+    test "cache_key for queries with offset which return 0 rows" do
+      developers = Developer.offset(20)
+      assert_match(/\Adevelopers\/query-(\h+)-0\Z/, developers.cache_key)
+    end
   end
 end