Add Retrieve An Object If It Exists as a rails til.

README.md

@@ -68,6 +68,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Conditional Class Selectors in Haml](rails/conditional-class-selectors-in-haml.md)
 - [Creating Records of Has_One Associations](rails/creating-records-of-has-one-associations.md)
 - [Pretend Generations](rails/pretend-generations.md)
+- [Retrieve An Object If It Exists](rails/retrieve-an-object-if-it-exists.md)
 - [Show Pending Migrations](rails/show-pending-migrations.md)
 
 ### ruby

rails/retrieve-an-object-if-it-exists.md

@@ -0,0 +1,19 @@
+# Retrieve An Object If It Exists
+
+Rails' Active Support provides the `blank?` and `present?` convenience
+methods as extensions to many objects. It also extends the Object class by
+providing the [`presence`](http://api.rubyonrails.org/classes/Object.html#method-i-presence)
+method. This method returns the *receiver* if it is not blank, otherwise
+it returns nil.
+
+Instead of doing
+
+```ruby
+User.nickname.present? ? User.nickname : User.firstname
+```
+
+I can simply do
+
+```ruby
+User.nickname.presence || User.firstname
+```