Merge pull request #1807 from caius/find_in_batches_id_bug

Bugfix by stopping find_in_batches using the records after yielding.

activerecord/lib/active_record/relation/batches.rb

@@ -66,11 +66,14 @@ module ActiveRecord
       records = relation.where(table[primary_key].gteq(start)).all
 
       while records.any?
+        records_size = records.size
+        primary_key_offset = records.last.id
+
         yield records
 
-        break if records.size < batch_size
+        break if records_size < batch_size
 
-        if primary_key_offset = records.last.id
+        if primary_key_offset
           records = relation.where(table[primary_key].gt(primary_key_offset)).to_a
         else
           raise "Primary key not included in the custom select clause"

activerecord/test/cases/batches_test.rb

@@ -100,4 +100,20 @@ class EachTest < ActiveRecord::TestCase
       end
     end
   end
+
+  def test_find_in_batches_should_not_use_records_after_yielding_them_in_case_original_array_is_modified
+    not_a_post = "not a post"
+    not_a_post.stubs(:id).raises(StandardError, "not_a_post had #id called on it")
+
+    assert_nothing_raised do
+      Post.find_in_batches(:batch_size => 1) do |batch|
+        assert_kind_of Array, batch
+        assert_kind_of Post, batch.first
+
+        batch.map! { not_a_post }
+      end
+    end
+
+  end
+
 end