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, 19 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index f9e69533c7..56aba1c483 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,22 @@
+*   Add `ActiveRecord::Relation#in_batches` to work with records and relations
+    in batches.
+
+    Available options are `of` (batch size), `load`, `begin_at`, and `end_at`.
+
+    Examples:
+
+        Person.in_batches.each_record(&:party_all_night!)
+        Person.in_batches.update_all(awesome: true)
+        Person.in_batches.delete_all
+        Person.in_batches.each do |relation|
+          relation.delete_all
+          sleep 10 # Throttles the delete queries
+        end
+
+    Closes #20933.
+
+    *Sina Siadat*
+
 *   Added methods for PostgreSQL geometric data types to use in migrations
 
     Example: