Move using_distinct_on? to PostgreSQL compiler. Extract order tweaking

to a new method.

2 files changed, 12 insertions, 9 deletions

diff --git a/lib/arel/engines/sql/compilers/postgresql_compiler.rb b/lib/arel/engines/sql/compilers/postgresql_compiler.rb
index c3360b53a5..809485bb4d 100644
--- a/lib/arel/engines/sql/compilers/postgresql_compiler.rb
+++ b/lib/arel/engines/sql/compilers/postgresql_compiler.rb
@@ -4,10 +4,6 @@ module Arel
 
       def select_sql
         if !orders.blank? && using_distinct_on?
-          # PostgreSQL does not allow arbitrary ordering when using DISTINCT ON, so we work around this
-          # by wrapping the +sql+ string as a sub-select and ordering in that query.
-          order = order_clauses.join(', ').split(',').map { |s| s.strip }.reject(&:blank?)
-          order = order.zip((0...order.size).to_a).map { |s,i| "id_list.alias_#{i} #{'DESC' if s =~ /\bdesc$/i}" }.join(', ')
 
           query = build_query \
             "SELECT #{select_clauses.kind_of?(::Array) ? select_clauses.join("") : select_clauses.to_s}",
@@ -20,7 +16,7 @@ module Arel
 
           build_query \
             "SELECT * FROM (#{query}) AS id_list",
-            "ORDER BY #{order}",
+            "ORDER BY #{aliased_orders(order_clauses)}",
             ("LIMIT #{taken}" unless taken.blank? ),
             ("OFFSET #{skipped}" unless skipped.blank? )
 
@@ -28,6 +24,17 @@ module Arel
           super
         end
       end
+
+      def using_distinct_on?
+        select_clauses.any? { |x| x =~ /DISTINCT ON/ }
+      end
+
+      def aliased_orders(orders)
+        # PostgreSQL does not allow arbitrary ordering when using DISTINCT ON, so we work around this
+        # by wrapping the +sql+ string as a sub-select and ordering in that query.
+        order = orders.join(', ').split(/,/).map { |s| s.strip }.reject(&:blank?)
+        order = order.zip((0...order.size).to_a).map { |s,i| "id_list.alias_#{i} #{'DESC' if s =~ /\bdesc$/i}" }.join(', ')
+      end
     end
   end
 end
diff --git a/lib/arel/engines/sql/relations/compiler.rb b/lib/arel/engines/sql/relations/compiler.rb
index 6026fc126f..b85d227705 100644
--- a/lib/arel/engines/sql/relations/compiler.rb
+++ b/lib/arel/engines/sql/relations/compiler.rb
@@ -53,10 +53,6 @@ module Arel
       def order_clauses
         orders.collect { |o| o.to_sql(Sql::OrderClause.new(relation)) }
       end
-
-      def using_distinct_on?
-        select_clauses.any? { |x| x =~ /DISTINCT ON/ }
-      end
     end
 
   end