Query guide: scopes with arguments should be instead defined as class methods.

1 files changed, 31 insertions, 3 deletions

diff --git a/railties/guides/source/active_record_querying.textile b/railties/guides/source/active_record_querying.textile
index 5cd302f356..eb77a35739 100644
--- a/railties/guides/source/active_record_querying.textile
+++ b/railties/guides/source/active_record_querying.textile
@@ -768,13 +768,41 @@ h4. Working with times
 If you're working with dates or times within scopes, due to how they are evaluated, you will need to use a lambda so that the scope is evaluated every time.
 
 <ruby>
-  class Post < ActiveRecord::Base
-    scope :last_week, lambda { where("created_at < ?", Time.zone.now ) }
-  end
+class Post < ActiveRecord::Base
+  scope :last_week, lambda { where("created_at < ?", Time.zone.now ) }
+end
 </ruby>
 
 Without the +lambda+, this +Time.zone.now+ will only be called once.
 
+h4. Passing in arguments
+
+When a +lambda+ is used for a +scope+, it can take arguments:
+
+<ruby>
+class Post < ActiveRecord::Base
+  scope :1_week_before, lambda { |time| where("created_at < ?", time)
+end
+</ruby>
+
+This may then be called using this:
+
+<ruby>
+Post.1_week_before(Time.zone.now)
+</ruby>
+
+However, this is just duplicating the functionality that would be provided to you by a class method.
+
+<ruby>
+class Post < ActiveRecord::Base
+  def self.1_week_before(time)
+    where("created_at < ?", time)
+  end
+end
+</ruby>
+
+Using a class method is the preferred way to accept arguments for scopes.
+
 h3. Dynamic Finders
 
 For every field (also known as an attribute) you define in your table, Active Record provides a finder method. If you have a field called +first_name+ on your +Client+ model for example, you get +find_by_first_name+ and +find_all_by_first_name+ for free from Active Record. If you have a +locked+ field on the +Client+ model, you also get +find_by_locked+ and +find_all_by_locked+ methods.