update is working on the select manager

lib/arel/select_manager.rb

@@ -26,6 +26,15 @@ def take limit
       self
     end
 
+    # FIXME: this method should go away
+    def update values
+      um = UpdateManager.new @engine
+      um.table values.first.first.relation
+      um.set values
+      um.wheres = @ctx.wheres
+      @engine.connection.execute um.to_sql
+    end
+
     # FIXME: this method should go away
     def insert values
       im = InsertManager.new @engine

lib/arel/update_manager.rb

@@ -12,6 +12,10 @@ def table table
       self
     end
 
+    def wheres= exprs
+      @head.wheres = exprs
+    end
+
     def where expr
       @head.wheres << expr
       self

lib/arel/visitors/to_sql.rb

@@ -16,7 +16,7 @@ def visit_Arel_Nodes_UpdateStatement o
         [
           "UPDATE #{visit o.relation}",
           ("SET #{o.values.map { |column,value|
-              "#{quote_column_name(column.name)} = #{quote visit value}"
+              "#{quote_column_name(column.name)} = #{value ? quote(visit(value)) : 'NULL'}"
             }.join ', '}" unless o.values.empty?),
           ("WHERE #{o.wheres.map { |x| visit x }.join ' AND '}" unless o.wheres.empty?)
         ].compact.join ' '

spec/arel/select_manager_spec.rb

 require 'spec_helper'
 
 module Arel
+  class EngineProxy
+    attr_reader :executed
+
+    def initialize engine
+      @engine = engine
+      @executed = []
+    end
+
+    def connection
+      self
+    end
+
+    def quote_table_name thing; @engine.connection.quote_table_name thing end
+    def quote_column_name thing; @engine.connection.quote_column_name thing end
+    def quote thing, column; @engine.connection.quote thing, column end
+
+    def execute sql
+      @executed << sql
+    end
+  end
+
   describe 'select manager' do
+    describe 'update' do
+      it 'copies where clauses' do
+        engine  = EngineProxy.new Table.engine
+        table   = Table.new :users
+        manager = Arel::SelectManager.new engine
+        manager.where table[:id].eq 10
+        manager.from table
+        manager.update(table[:id] => 1)
+
+        engine.executed.last.should be_like %{
+          UPDATE "users" SET "id" = 1 WHERE "users"."id" = 10
+        }
+      end
+
+      it 'executes an update statement' do
+        engine  = EngineProxy.new Table.engine
+        table   = Table.new :users
+        manager = Arel::SelectManager.new engine
+        manager.from table
+        manager.update(table[:id] => 1)
+
+        engine.executed.last.should be_like %{
+          UPDATE "users" SET "id" = 1
+        }
+      end
+    end
+
     describe 'project' do
       it 'takes strings' do
         table   = Table.new :users

spec/arel/update_manager_spec.rb

@@ -9,6 +9,14 @@ module Arel
     end
 
     describe 'set' do
+      it "updates with null" do
+        table = Table.new(:users)
+        um = Arel::UpdateManager.new Table.engine
+        um.table table
+        um.set [[table[:name], nil]]
+        um.to_sql.should be_like %{ UPDATE "users" SET "name" =  NULL }
+      end
+
       it 'takes a list of lists' do
         table = Table.new(:users)
         um = Arel::UpdateManager.new Table.engine