Make implicit order column configurable

When calling ordered finder methods such as +first+ or +last+ without an
explicit order clause, ActiveRecord sorts records by primary key. This
can result in unpredictable and surprising behaviour when the primary
key is not an auto-incrementing integer, for example when it's a UUID.
This change makes it possible to override the column used for implicit
ordering such that +first+ and +last+ will return more predictable
results. For Example:

  class Project < ActiveRecord::Base
    self.implicit_order_column = "created_at"
  end

1 files changed, 2 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index afaa900442..dc03b196f4 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -550,8 +550,8 @@ module ActiveRecord
       end
 
       def ordered_relation
-        if order_values.empty? && primary_key
-          order(arel_attribute(primary_key).asc)
+        if order_values.empty? && (implicit_order_column || primary_key)
+          order(arel_attribute(implicit_order_column || primary_key).asc)
         else
           self
         end