Add ActiveRecord.count documentation when used on group relations

1 files changed, 6 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index f10c290755..3fc079d84c 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -13,6 +13,12 @@ module ActiveRecord
     #
     #   Person.count(:age, distinct: true)
     #   # => counts the number of different age values
+    #
+    # If used on a +group+, it returns a Hash whose keys represent the aggregated column,
+    # and the values are the respective amounts:
+    #
+    #   Person.group(:city).count
+    #   # => { 'Rome' => 5, 'Paris' => 3 }
     def count(column_name = nil, options = {})
       column_name, options = nil, column_name if column_name.is_a?(Hash)
       calculate(:count, column_name, options)