adding locking node to the AST

lib/arel/nodes.rb

@@ -4,6 +4,7 @@
 require 'arel/nodes/and'
 
 require 'arel/nodes/in'
+require 'arel/nodes/lock'
 require 'arel/nodes/function'
 require 'arel/nodes/count'
 require 'arel/nodes/sum'

lib/arel/nodes/lock.rb

+module Arel
+  module Nodes
+    class Lock
+    end
+  end
+end

lib/arel/nodes/select_statement.rb

@@ -2,12 +2,13 @@ module Arel
   module Nodes
     class SelectStatement
       attr_reader :cores
-      attr_accessor :limit, :orders
+      attr_accessor :limit, :orders, :lock
 
       def initialize cores = [SelectCore.new]
         @cores  = cores
         @orders = []
         @limit  = nil
+        @lock   = nil
       end
 
       def initialize_copy other

lib/arel/select_manager.rb

@@ -8,6 +8,13 @@ def initialize engine
       @ctx    = @head.cores.last
     end
 
+    def lock locking = true
+      # FIXME: do we even need to store this?  If locking is +false+ shouldn't
+      # we just remove the node from the AST?
+      @head.lock = Nodes::Lock.new
+      self
+    end
+
     def on *exprs
       @ctx.froms.last.constraint = Nodes::On.new(collapse(exprs))
       self

lib/arel/table.rb

@@ -26,6 +26,10 @@ def tm
       SelectManager.new(@engine).from(self)
     end
 
+    def from table
+      SelectManager.new(@engine).from table
+    end
+
     def joins manager
       nil
     end

lib/arel/visitors/to_sql.rb

@@ -48,7 +48,8 @@ def visit_Arel_Nodes_SelectStatement o
         [
           o.cores.map { |x| visit x }.join,
           ("ORDER BY #{o.orders.map { |x| visit x }.join(', ')}" unless o.orders.empty?),
-          ("LIMIT #{o.limit}" if o.limit)
+          ("LIMIT #{o.limit}" if o.limit),
+          (visit(o.lock) if o.lock),
         ].compact.join ' '
       end
 
@@ -66,6 +67,11 @@ def visit_Arel_Nodes_Having o
         "HAVING #{visit o.expr}"
       end
 
+      # FIXME: this does nothing on SQLLite3, but should do things on other
+      # databases.
+      def visit_Arel_Nodes_Lock o
+      end
+
       def visit_Arel_Nodes_Group o
         visit o.expr
       end

spec/arel/select_manager_spec.rb

@@ -25,6 +25,15 @@ def execute sql, name = nil
   end
 
   describe 'select manager' do
+    describe 'lock' do
+      # This should fail on other databases
+      it 'adds a lock node' do
+        table   = Table.new :users
+        mgr = table.from table
+        mgr.lock.to_sql.should be_like %{ SELECT FROM "users" }
+      end
+    end
+
     describe 'order' do
       it 'generates order clauses' do
         table   = Table.new :users