clear and disable query cache when an exception is raised from called middleware

activerecord/lib/active_record/query_cache.rb

@@ -61,6 +61,12 @@ module ActiveRecord
 
       status, headers, body = @app.call(env)
       [status, headers, BodyProxy.new(old, body)]
+    rescue Exception => e
+      ActiveRecord::Base.connection.clear_query_cache
+      unless old
+        ActiveRecord::Base.connection.disable_query_cache!
+      end
+      raise e
     end
   end
 end

activerecord/test/cases/query_cache_test.rb

@@ -13,6 +13,32 @@ class QueryCacheTest < ActiveRecord::TestCase
     ActiveRecord::Base.connection.disable_query_cache!
   end
 
+  def test_exceptional_middleware_clears_and_disables_cache_on_error
+    assert !ActiveRecord::Base.connection.query_cache_enabled, 'cache off'
+
+    mw = ActiveRecord::QueryCache.new lambda { |env|
+      Task.find 1
+      Task.find 1
+      assert_equal 1, ActiveRecord::Base.connection.query_cache.length
+      raise "lol borked"
+    }
+    assert_raises(RuntimeError) { mw.call({}) }
+
+    assert_equal 0, ActiveRecord::Base.connection.query_cache.length
+    assert !ActiveRecord::Base.connection.query_cache_enabled, 'cache off'
+  end
+
+  def test_exceptional_middleware_leaves_enabled_cache_alone
+    ActiveRecord::Base.connection.enable_query_cache!
+
+    mw = ActiveRecord::QueryCache.new lambda { |env|
+      raise "lol borked"
+    }
+    assert_raises(RuntimeError) { mw.call({}) }
+
+    assert ActiveRecord::Base.connection.query_cache_enabled, 'cache off'
+  end
+
   def test_middleware_delegates
     called = false
     mw = ActiveRecord::QueryCache.new lambda { |env|
@@ -213,4 +239,4 @@ class QueryCacheBodyProxyTest < ActiveRecord::TestCase
     assert_equal proxy.to_path, "/path"
   end
 
-end
+end