basic updates are working

lib/arel.rb

@@ -10,6 +10,7 @@ require 'arel/relation'
 require 'arel/tree_manager'
 require 'arel/insert_manager'
 require 'arel/select_manager'
+require 'arel/update_manager'
 require 'arel/nodes'
 
 #### these are deprecated

lib/arel/nodes.rb

@@ -3,3 +3,4 @@ require 'arel/nodes/sql_literal'
 require 'arel/nodes/select_core'
 require 'arel/nodes/select_statement'
 require 'arel/nodes/insert_statement'
+require 'arel/nodes/update_statement'

lib/arel/nodes/update_statement.rb

@@ -0,0 +1,12 @@
+module Arel
+  module Nodes
+    class UpdateStatement
+      attr_accessor :relation, :wheres
+
+      def initialize
+        @relation = nil
+        @wheres   = []
+      end
+    end
+  end
+end

lib/arel/update_manager.rb

@@ -0,0 +1,20 @@
+module Arel
+  class UpdateManager < Arel::TreeManager
+    def initialize engine
+      super
+      @head = Nodes::UpdateStatement.new
+    end
+
+    ###
+    # UPDATE +table+
+    def table table
+      @head.relation = table
+      self
+    end
+
+    def where expr
+      @head.wheres << expr
+      self
+    end
+  end
+end

lib/arel/visitors/to_sql.rb

@@ -12,6 +12,13 @@ module Arel
       end
 
       private
+      def visit_Arel_Nodes_UpdateStatement o
+        [
+          "UPDATE #{visit o.relation}",
+          ("WHERE #{o.wheres.map { |x| visit x }.join ' AND '}" unless o.wheres.empty?)
+        ].compact.join ' '
+      end
+
       def visit_Arel_Nodes_InsertStatement o
         [
           "INSERT INTO #{visit o.relation}",

spec/arel/update_manager_spec.rb

@@ -0,0 +1,43 @@
+require 'spec_helper'
+
+module Arel
+  describe 'update manager' do
+    describe 'new' do
+      it 'takes an engine' do
+        Arel::UpdateManager.new Table.engine
+      end
+    end
+
+    describe 'table' do
+      it 'generates an update statement' do
+        um = Arel::UpdateManager.new Table.engine
+        um.table Table.new(:users)
+        um.to_sql.should be_like %{ UPDATE "users" }
+      end
+
+      it 'chains' do
+        um = Arel::UpdateManager.new Table.engine
+        um.table(Table.new(:users)).should == um
+      end
+    end
+
+    describe 'where' do
+      it 'generates a where clause' do
+        table = Table.new :users
+        um = Arel::UpdateManager.new Table.engine
+        um.table table
+        um.where table[:id].eq(1)
+        um.to_sql.should be_like %{
+          UPDATE "users" WHERE "users"."id" = 1
+        }
+      end
+
+      it 'chains' do
+        table = Table.new :users
+        um = Arel::UpdateManager.new Table.engine
+        um.table table
+        um.where(table[:id].eq(1)).should == um
+      end
+    end
+  end
+end