Add ActiveRecord::Relation#in_batches

`in_batches` yields Relation objects if a block is given, otherwise it
returns an instance of `BatchEnumerator`. The existing `find_each` and
`find_in_batches` methods work with batches of records. The new API
allows working with relation batches as well.

Examples:

    Person.in_batches.each_record(&:party_all_night!)
    Person.in_batches.update_all(awesome: true)
    Person.in_batches.delete_all
    Person.in_batches.map do |relation|
      relation.delete_all
      sleep 10 # Throttles the delete queries
    end

1 files changed, 7 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index 3ed04dee3b..e47b7b1ed9 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -667,6 +667,13 @@ module ActiveRecord
       "#<#{self.class.name} [#{entries.join(', ')}]>"
     end
 
+    protected
+
+      def load_records(records)
+        @records = records
+        @loaded = true
+      end
+
     private
 
     def exec_queries