Add rails 016

docs/ruby_on_rails/016.md

@@ -0,0 +1,23 @@
+# Find records missing an association with `where.missing`
+
+In rails 6.1 you can find all records missing an association without `left_joins`
+
+```ruby
+class Account < ApplicationRecord
+  has_many :recovery_email_addresses
+end
+
+# Before Rails 6.1
+Account.left_joins(:recovery_email_addresses).where(recovery_email_addresses: { id: nil })
+
+# After Rails 6.1
+Account.where.missing(:recovery_email_addresses)
+```
+
+- [link](https://boringrails.com/tips/activerecord-where-missing-associations)
+
+There is also rubocop rule for that [Rails/WhereMissing](https://docs.rubocop.org/rubocop-rails/cops_rails.html#railswheremissing)
+
+
+
+

docs/ruby_on_rails/README.md

@@ -19,6 +19,7 @@ Welcome to Ruby on Rails page. Please open menu and enjoy.
 - [Railsdiff](ruby_on_rails/013.md)
 - [find vs find_by](ruby_on_rails/014.md)
 - [preload vs includes](ruby_on_rails/015.md)
+= [missing an association with where.missing](ruby_on_rails/016.md)
 
 ## Links