Allow order to be given expressions as hash keys

When `order` is given a hash, the keys are currently assumed to be
attribute names and are quoted as such in the query, which makes it
impossible to pass an expression instead:

    Post.order("LENGTH(title)" => :asc).last
    # SELECT  `posts`.* FROM `posts` ORDER BY `posts`.`LENGTH(title)` DESC LIMIT 1

If the key is an `Arel::Nodes::SqlLiteral`, we now use it directly in
the query. This provides a way to build a relation with a complex order
clause that can still be reversed with `reverse_order` or `last`.

1 files changed, 6 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 4ee413c805..1178dec706 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -1130,7 +1130,12 @@ module ActiveRecord
             arel_attribute(arg).asc
           when Hash
             arg.map { |field, dir|
-              arel_attribute(field).send(dir.downcase)
+              case field
+              when Arel::Nodes::SqlLiteral
+                field.send(dir.downcase)
+              else
+                arel_attribute(field).send(dir.downcase)
+              end
             }
           else
             arg