differentiating equality and assignment

lib/arel/nodes.rb

 require 'arel/nodes/binary'
 require 'arel/nodes/equality'
+require 'arel/nodes/assignment'
 require 'arel/nodes/or'
 require 'arel/nodes/and'
 require 'arel/nodes/greater_than'

lib/arel/nodes/assignment.rb

+module Arel
+  module Nodes
+    class Assignment < Arel::Nodes::Binary
+    end
+  end
+end

lib/arel/update_manager.rb

@@ -26,7 +26,7 @@ def set values
         @head.values = [values]
       else
         @head.values = values.map { |column,value|
-          Nodes::Equality.new(
+          Nodes::Assignment.new(
             Nodes::UnqualifiedColumn.new(column),
             value
           )

lib/arel/visitors/to_sql.rb

@@ -149,13 +149,24 @@ def visit_Arel_Nodes_Or o
         "#{visit o.left} OR #{visit o.right}"
       end
 
-      def visit_Arel_Nodes_Equality o
+      def visit_Arel_Nodes_Assignment o
         right = o.right
-        # FIXME: maybe we should visit NilClass?
+
         right = right.nil? ? 'NULL' : visit(right)
         "#{visit o.left} = #{right}"
       end
 
+      def visit_Arel_Nodes_Equality o
+        right = o.right
+
+        # FIXME: maybe we should visit NilClass?
+        if right.nil?
+          "#{visit o.left} IS NULL"
+        else
+          "#{visit o.left} = #{visit right}"
+        end
+      end
+
       def visit_Arel_Nodes_UnqualifiedColumn o
         "#{quote_column_name o.name}"
       end