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`.

2 files changed, 30 insertions, 2 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
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 0c94e891eb..b7c3406fbb 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -218,17 +218,34 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal topics(:fifth).title, topics.first.title
   end
 
-  def test_finding_with_reverted_assoc_order
+  def test_finding_with_arel_assoc_order
+    topics = Topic.order(Arel.sql("id") => :desc)
+    assert_equal 5, topics.to_a.size
+    assert_equal topics(:fifth).title, topics.first.title
+  end
+
+  def test_finding_with_reversed_assoc_order
     topics = Topic.order(id: :asc).reverse_order
     assert_equal 5, topics.to_a.size
     assert_equal topics(:fifth).title, topics.first.title
   end
 
+  def test_finding_with_reversed_arel_assoc_order
+    topics = Topic.order(Arel.sql("id") => :asc).reverse_order
+    assert_equal 5, topics.to_a.size
+    assert_equal topics(:fifth).title, topics.first.title
+  end
+
   def test_reverse_order_with_function
     topics = Topic.order("length(title)").reverse_order
     assert_equal topics(:second).title, topics.first.title
   end
 
+  def test_reverse_arel_assoc_order_with_function
+    topics = Topic.order(Arel.sql("length(title)") => :asc).reverse_order
+    assert_equal topics(:second).title, topics.first.title
+  end
+
   def test_reverse_order_with_function_other_predicates
     topics = Topic.order("author_name, length(title), id").reverse_order
     assert_equal topics(:second).title, topics.first.title
@@ -251,6 +268,12 @@ class RelationTest < ActiveRecord::TestCase
     end
   end
 
+  def test_reverse_arel_assoc_order_with_multiargument_function
+    assert_nothing_raised do
+      Topic.order(Arel.sql("REPLACE(title, '', '')") => :asc).reverse_order
+    end
+  end
+
   def test_reverse_order_with_nulls_first_or_last
     assert_raises(ActiveRecord::IrreversibleOrderError) do
       Topic.order("title NULLS FIRST").reverse_order