Add Get An Empty ActiveRecord Relation as a rails til

README.md

@@ -9,7 +9,7 @@ and pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://tinyletter.com/jbranchaud).
 
-_938 TILs and counting..._
+_939 TILs and counting..._
 
 ---
 
@@ -580,6 +580,7 @@ _938 TILs and counting..._
 - [Force All Users To Sign Out](rails/force-all-users-to-sign-out.md)
 - [Generating And Executing SQL](rails/generating-and-executing-sql.md)
 - [Get An Array Of Values From The Database](rails/get-an-array-of-values-from-the-database.md)
+- [Get An Empty ActiveRecord Relation](rails/get-an-empty-activerecord-relation.md)
 - [Get The Column Names For A Model](rails/get-the-column-names-for-a-model.md)
 - [Hash Slicing](rails/hash-slicing.md)
 - [Ignore Poltergeist JavaScript Errors](rails/ignore-poltergeist-javascript-errors.md)

rails/get-an-empty-activerecord-relation.md

@@ -0,0 +1,33 @@
+# Get An Empty ActiveRecord Relation
+
+When you query for something (with `#where`) and there are no results matching
+that query, you get something that looks like an empty array (`[]`), but it's
+not quite.
+
+```ruby
+> result
+[]
+> result.class
+Book::ActiveRecord_Relation
+```
+
+It's an empty [`ActiveRecord`
+relation](https://api.rubyonrails.org/classes/ActiveRecord/Relation.html).
+
+You can get an instance of an empty `ActiveRecord` relation without
+constructing a _no result_ query.
+
+```ruby
+> Book.none
+[]
+> Book.none.class
+Book::ActiveRecord_Relation
+```
+
+I can think of a couple scenarios where this would be useful:
+
+- as a default value for a method parameter
+- as a test value for a method that expects to have an `ActiveRecord` relation
+  passed in
+
+[source](https://stackoverflow.com/questions/4877931/how-to-return-an-empty-activerecord-relation)