Merge pull request #13201 from marcandre/find_in_batch_enumerator

`find_in_batches` now returns an `Enumerator`

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/lib/active_record/relation/batches.rb

3 files changed, 27 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 6226ce844f..fe0d7b2b35 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,8 @@
+*   `find_in_batches` now returns an `Enumerator` when called without a block, so that it
+    can be chained with other `Enumerable` methods.
+
+    *Marc-André Lafortune*
+
 *   `enum` now raises on "dangerous" name conflicts
 
     Dangerous name conflicts includes instance or class method conflicts
diff --git a/activerecord/lib/active_record/relation/batches.rb b/activerecord/lib/active_record/relation/batches.rb
index e98b4712f5..dfcfef2ad2 100644
--- a/activerecord/lib/active_record/relation/batches.rb
+++ b/activerecord/lib/active_record/relation/batches.rb
@@ -64,6 +64,14 @@ module ActiveRecord
     #     group.each { |person| person.party_all_night! }
     #   end
     #
+    # If you do not provide a block to #find_in_batches, it will return an Enumerator
+    # for chaining with other methods:
+    #
+    #   Person.find_in_batches.with_index do |group, batch|
+    #     puts "Processing group ##{batch}"
+    #     group.each(&:recover_from_last_night!)
+    #   end
+    #
     # To be yielded each record one by one, use #find_each instead.
     #
     # ==== Options
@@ -88,6 +96,7 @@ module ActiveRecord
     # the batch sizes.
     def find_in_batches(options = {})
       options.assert_valid_keys(:start, :batch_size)
+      return to_enum(:find_in_batches, options) unless block_given?
 
       relation = self
 
diff --git a/activerecord/test/cases/batches_test.rb b/activerecord/test/cases/batches_test.rb
index ebb36e4940..1161b57514 100644
--- a/activerecord/test/cases/batches_test.rb
+++ b/activerecord/test/cases/batches_test.rb
@@ -172,4 +172,17 @@ class EachTest < ActiveRecord::TestCase
       end
     end
   end
+
+  def test_find_in_batches_should_return_an_enumerator
+    enum = nil
+    assert_queries(0) do
+      enum = Post.find_in_batches(:batch_size => 1)
+    end
+    assert_queries(4) do
+      enum.first(4) do |batch|
+        assert_kind_of Array, batch
+        assert_kind_of Post, batch.first
+      end
+    end
+  end
 end