Added support of nulls first/last expression

lib/arel/nodes.rb

@@ -14,6 +14,7 @@
 # unary
 require 'arel/nodes/unary'
 require 'arel/nodes/grouping'
+require 'arel/nodes/ordering'
 require 'arel/nodes/ascending'
 require 'arel/nodes/descending'
 require 'arel/nodes/unqualified_column'

lib/arel/nodes/ascending.rb

@@ -3,7 +3,7 @@ module Nodes
     class Ascending < Ordering
 
       def reverse
-        Descending.new(expr)
+        Descending.new(expr, nulls: reverse_nulls)
       end
 
       def direction

lib/arel/nodes/descending.rb

@@ -3,7 +3,7 @@ module Nodes
     class Descending < Ordering
 
       def reverse
-        Ascending.new(expr)
+        Ascending.new(expr, nulls: reverse_nulls)
       end
 
       def direction

lib/arel/nodes/ordering.rb

@@ -0,0 +1,27 @@
+module Arel
+  module Nodes
+    class Ordering < Unary
+      REVERSE_NULLS = { first: :last, last: :first }
+
+      attr_accessor :nulls
+
+      def initialize(expr, options = {})
+        super(expr)
+        @nulls = options[:nulls]
+      end
+
+      def hash
+        [@expr, @nulls].hash
+      end
+
+      def eql?(other)
+        super && self.nulls == other.nulls
+      end
+
+      protected
+        def reverse_nulls
+          REVERSE_NULLS.fetch(nulls, nil)
+        end
+    end
+  end
+end

lib/arel/nodes/unary.rb

@@ -28,7 +28,6 @@ def eql? other
       Not
       Offset
       On
-      Ordering
       Top
       Lock
       DistinctOn

lib/arel/order_predications.rb

@@ -1,12 +1,12 @@
 module Arel
   module OrderPredications
 
-    def asc
-      Nodes::Ascending.new self
+    def asc(*args)
+      Nodes::Ascending.new self, *args
     end
 
-    def desc
-      Nodes::Descending.new self
+    def desc(*args)
+      Nodes::Descending.new self, *args
     end
 
   end

lib/arel/visitors/ibm_db.rb

@@ -8,7 +8,6 @@ def visit_Arel_Nodes_Limit o, collector
         collector = visit o.expr, collector
         collector << " ROWS ONLY"
       end
-
     end
   end
 end

lib/arel/visitors/oracle.rb

@@ -115,6 +115,12 @@ def order_hacks o
         o
       end
 
+      def visit_ordering_node(o, collector, direction)
+        collector = visit(o.expr, collector) << ' ' << direction
+        collector << " NULLS #{o.nulls.to_s.upcase}" if o.nulls
+        collector
+      end
+
       # Split string by commas but count opening and closing brackets
       # and ignore commas inside brackets.
       def split_order_string(string)

lib/arel/visitors/postgresql.rb

@@ -23,6 +23,12 @@ def visit_Arel_Nodes_DistinctOn o, collector
         collector << "DISTINCT ON ( "
         visit(o.expr, collector) << " )"
       end
+
+      def visit_ordering_node(o, collector, direction)
+        collector = visit(o.expr, collector) << ' ' << direction
+        collector << " NULLS #{o.nulls.to_s.upcase}" if o.nulls
+        collector
+      end
     end
   end
 end

lib/arel/visitors/to_sql.rb

@@ -450,12 +450,12 @@ def visit_Arel_SelectManager o, collector
         collector << "(#{o.to_sql.rstrip})"
       end
 
-      def visit_Arel_Nodes_Ascending o, collector
-        visit(o.expr, collector) << " ASC"
+      def visit_Arel_Nodes_Ascending(o, collector)
+        visit_ordering_node(o, collector, 'ASC')
       end
 
-      def visit_Arel_Nodes_Descending o, collector
-        visit(o.expr, collector) << " DESC"
+      def visit_Arel_Nodes_Descending(o, collector)
+        visit_ordering_node(o, collector, 'DESC')
       end
 
       def visit_Arel_Nodes_Group o, collector
@@ -819,6 +819,21 @@ def aggregate name, o, collector
           collector
         end
       end
+
+      def visit_ordering_node(o, collector, direction)
+        if o.nulls
+          collector << 'CASE WHEN '
+
+          ordering_expr = compile(o.expr)
+
+          collector << ordering_expr
+          collector << [' IS NULL THEN 0 ELSE 1 END', o.nulls == :first ? 'ASC' : 'DESC'].join(' ')
+          collector << ', '
+          collector << ordering_expr
+        else
+          visit(o.expr, collector)
+        end << ' ' << direction
+      end
     end
   end
 end

test/nodes/test_ascending.rb

@@ -39,6 +39,20 @@ def test_inequality_with_different_ivars
         array = [Ascending.new('zomg'), Ascending.new('zomg!')]
         assert_equal 2, array.uniq.size
       end
+
+      def test_accept_nulls_first_last_option
+        ascending = Ascending.new('zomg')
+        assert_nil ascending.nulls
+
+        ascending = Ascending.new('zomg', nulls: :first)
+        assert_equal :first, ascending.nulls
+      end
+
+      def test_reverse_with_nulls
+        ascending = Ascending.new('zomg', nulls: :first)
+        descending = ascending.reverse
+        assert_equal :last, descending.nulls
+      end
     end
   end
 end

test/nodes/test_descending.rb

@@ -39,6 +39,20 @@ def test_inequality_with_different_ivars
         array = [Descending.new('zomg'), Descending.new('zomg!')]
         assert_equal 2, array.uniq.size
       end
+
+      def test_accept_nulls_first_last_option
+        ascending = Descending.new('zomg')
+        assert_nil ascending.nulls
+
+        ascending = Descending.new('zomg', nulls: :last)
+        assert_equal :last, ascending.nulls
+      end
+
+      def test_reverse_with_nulls
+        ascending = Descending.new('zomg', nulls: :last)
+        descending = ascending.reverse
+        assert_equal :first, descending.nulls
+      end
     end
   end
 end

test/visitors/test_ibm_db.rb

@@ -27,7 +27,6 @@ def compile node
         sql = compile(stmt)
         sql.must_be_like "UPDATE \"users\" WHERE \"users\".\"id\" IN (SELECT \"users\".\"id\" FROM \"users\" FETCH FIRST 1 ROWS ONLY)"
       end
-
     end
   end
 end

test/visitors/test_oracle.rb

@@ -23,6 +23,20 @@ def compile node
         }
       end
 
+      it 'should support NULLS FIRST/LAST' do
+        compile(Nodes::Ascending.new(Nodes::SqlLiteral.new('omg'))).must_be_like %{
+           omg ASC
+        }
+
+        compile(Nodes::Ascending.new(Nodes::SqlLiteral.new('omg'), nulls: :first)).must_be_like %{
+          omg ASC NULLS FIRST
+        }
+
+        compile(Nodes::Descending.new(Nodes::SqlLiteral.new('omg'), nulls: :last)).must_be_like %{
+          omg DESC NULLS LAST
+        }
+      end
+
       it 'is idempotent with crazy query' do
         # *sigh*
         select = "DISTINCT foo.id, FIRST_VALUE(projects.name) OVER (foo) AS alias_0__"

test/visitors/test_postgres.rb

@@ -117,6 +117,11 @@ def compile node
           }
         end
       end
+
+      it 'should support NULLS FIRST/LAST' do
+        compile(@attr.asc).must_be_like %{ "users"."id" ASC }
+        compile(@attr.asc(nulls: :first)).must_be_like %{ "users"."id" ASC NULLS FIRST }
+      end
     end
   end
 end

test/visitors/test_to_sql.rb

@@ -359,6 +359,19 @@ def dispatch
             "users"."id" DESC
           }
         end
+
+        it 'should support NULLS FIRST' do
+          compile(@attr.asc(nulls: :first)).must_be_like %{
+            CASE WHEN "users"."id" IS NULL THEN 0 ELSE 1 END ASC, "users"."id" ASC
+          }
+        end
+
+        it 'should support NULLS LAST' do
+          compile(@attr.desc(nulls: :last)).must_be_like %{
+            CASE WHEN "users"."id" IS NULL THEN 0 ELSE 1 END DESC, "users"."id" DESC
+          }
+        end
+
       end
 
       describe "Nodes::In" do