adding more oracle hacks

lib/arel/visitors/oracle.rb

@@ -4,6 +4,8 @@ class Oracle < Arel::Visitors::ToSql
       private
 
       def visit_Arel_Nodes_SelectStatement o
+        order_hacks(o)
+
         if o.limit && o.orders.empty? && !o.offset
           o.cores.last.wheres.push Nodes::LessThanOrEqual.new(
             Nodes::SqlLiteral.new('ROWNUM'), o.limit
@@ -40,6 +42,23 @@ def visit_Arel_Nodes_SelectStatement o
       def visit_Arel_Nodes_Offset o
         "raw_rnum_ > #{visit o.value}"
       end
+
+      ###
+      # Hacks for the order clauses specific to Oracle
+      def order_hacks o
+        return if o.orders.empty?
+        return unless o.cores.any? do |core|
+          core.projections.any? do |projection|
+            /DISTINCT.*FIRST_VALUE/ === projection
+          end
+        end
+        orders = o.orders
+        o.orders = []
+        orders.each_with_index do |order, i|
+          o.orders <<
+            Nodes::SqlLiteral.new("alias_#{i}__ #{'DESC' if /\bdesc$/i === order}")
+        end
+      end
     end
   end
 end

spec/arel/visitors/oracle_spec.rb

@@ -7,6 +7,18 @@ module Visitors
         @visitor = Oracle.new Table.engine
       end
 
+      it 'modifies order when there is distinct and first value' do
+        # *sigh*
+        select = "DISTINCT foo.id, FIRST_VALUE(projects.name) OVER (foo) AS alias_0__"
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.projections << Nodes::SqlLiteral.new(select)
+        stmt.orders << Nodes::SqlLiteral.new('foo')
+        sql = @visitor.accept(stmt)
+        sql.should be_like %{
+          SELECT #{select} ORDER BY alias_0__
+        }
+      end
+
       describe 'Nodes::SelectStatement' do
         describe 'limit' do
           it 'adds a rownum clause' do