From ba7bbd390b6b4d69342a69d246b41b7abe4c6fa1 Mon Sep 17 00:00:00 2001
From: Tim Bleck <tim.bleck@webedia-group.com>
Date: Thu, 15 Jun 2017 09:57:35 +0200
Subject: [PATCH] [MODEL] Fix import when preprocess returns empty collection

Fixes #719
---
 .../model/adapters/active_record.rb           |  3 +-
 .../test/unit/adapter_active_record_test.rb   | 37 ++++++++++++++-----
 2 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/elasticsearch-model/lib/elasticsearch/model/adapters/active_record.rb b/elasticsearch-model/lib/elasticsearch/model/adapters/active_record.rb
index 23c4267fa..aa74833d4 100644
--- a/elasticsearch-model/lib/elasticsearch/model/adapters/active_record.rb
+++ b/elasticsearch-model/lib/elasticsearch/model/adapters/active_record.rb
@@ -103,7 +103,8 @@ def __find_in_batches(options={}, &block)
             scope = scope.instance_exec(&query) if query
 
             scope.find_in_batches(options) do |batch|
-              yield (preprocess ? self.__send__(preprocess, batch) : batch)
+              batch = self.__send__(preprocess, batch) if preprocess
+              yield(batch) if batch.present?
             end
           end
 
diff --git a/elasticsearch-model/test/unit/adapter_active_record_test.rb b/elasticsearch-model/test/unit/adapter_active_record_test.rb
index 335e3bd10..152526e47 100644
--- a/elasticsearch-model/test/unit/adapter_active_record_test.rb
+++ b/elasticsearch-model/test/unit/adapter_active_record_test.rb
@@ -121,20 +121,37 @@ def ids
         DummyClassForActiveRecord.__find_in_batches(query: -> { where(color: "red") }) do; end
       end
 
-      should "preprocess the batch if option provided" do
-        class << DummyClassForActiveRecord
-          # Updates/transforms the batch while fetching it from the database
-          # (eg. with information from an external system)
-          #
-          def update_batch(batch)
-            batch.collect { |b| b.to_s + '!' }
+      context "when preprocessing batches" do
+        setup do
+          class << DummyClassForActiveRecord
+            def find_in_batches(options = {}, &block)
+              yield [:a, :b]
+            end
+          end
+        end
+
+        should "preprocess the batch if option provided" do
+          class << DummyClassForActiveRecord
+            def update_batch(batch)
+              batch.collect { |b| b.to_s + '!' }
+            end
+          end
+
+          DummyClassForActiveRecord.__find_in_batches(preprocess: :update_batch) do |batch|
+            assert_same_elements ["a!", "b!"], batch
           end
         end
 
-        DummyClassForActiveRecord.expects(:__find_in_batches).returns( [:a, :b] )
+        should "skip batch if preprocess option provided and returns empty collection" do
+          class << DummyClassForActiveRecord
+            def update_batch(batch)
+              []
+            end
+          end
 
-        DummyClassForActiveRecord.__find_in_batches(preprocess: :update_batch) do |batch|
-          assert_same_elements ["a!", "b!"], batch
+          DummyClassForActiveRecord.__find_in_batches(preprocess: :update_batch) do |batch|
+            flunk("block should not have been called on empty batch")
+          end
         end
       end