adding an oracle visitor

lib/arel/nodes.rb

@@ -9,6 +9,7 @@ require 'arel/nodes/and'
 require 'arel/nodes/greater_than'
 require 'arel/nodes/greater_than_or_equal'
 require 'arel/nodes/less_than'
+require 'arel/nodes/less_than_or_equal'
 
 require 'arel/nodes/in'
 require 'arel/nodes/lock'

lib/arel/nodes/less_than_or_equal.rb

@@ -0,0 +1,6 @@
+module Arel
+  module Nodes
+    class LessThanOrEqual < Arel::Nodes::Binary
+    end
+  end
+end

lib/arel/visitors.rb

@@ -1,6 +1,7 @@
 require 'arel/visitors/to_sql'
 require 'arel/visitors/postgresql'
 require 'arel/visitors/mysql'
+require 'arel/visitors/oracle'
 require 'arel/visitors/join_sql'
 require 'arel/visitors/order_clauses'
 require 'arel/visitors/dot'
@@ -8,9 +9,10 @@ require 'arel/visitors/dot'
 module Arel
   module Visitors
     VISITORS = {
-      'postgresql' => Arel::Visitors::PostgreSQL,
-      'mysql'      => Arel::Visitors::MySQL,
-      'mysql2'     => Arel::Visitors::MySQL,
+      'postgresql'      => Arel::Visitors::PostgreSQL,
+      'mysql'           => Arel::Visitors::MySQL,
+      'mysql2'          => Arel::Visitors::MySQL,
+      'oracle_enhanced' => Arel::Visitors::Oracle,
     }
 
     ENGINE_VISITORS = Hash.new do |hash, engine|

lib/arel/visitors/oracle.rb

@@ -0,0 +1,15 @@
+module Arel
+  module Visitors
+    class Oracle < Arel::Visitors::ToSql
+      def visit_Arel_Nodes_SelectStatement o
+        if o.limit
+          o.cores.last.wheres.push Nodes::LessThanOrEqual.new(
+            Nodes::SqlLiteral.new('ROWNUM'), o.limit
+          )
+          o.limit = nil
+        end
+        super
+      end
+    end
+  end
+end

lib/arel/visitors/to_sql.rb

@@ -148,6 +148,10 @@ module Arel
         "#{visit o.left} > #{visit o.right}"
       end
 
+      def visit_Arel_Nodes_LessThanOrEqual o
+        "#{visit o.left} <= #{visit o.right}"
+      end
+
       def visit_Arel_Nodes_LessThan o
         "#{visit o.left} < #{visit o.right}"
       end

spec/arel/select_manager_spec.rb

@@ -15,6 +15,10 @@ module Arel
       @config = { :adapter => 'sqlite3' }
     end
 
+    def with_connection
+      yield self
+    end
+
     def connection
       self
     end

spec/arel/visitors/oracle_spec.rb

@@ -0,0 +1,22 @@
+require 'spec_helper'
+
+module Arel
+  module Visitors
+    describe 'the oracle visitor' do
+      before do
+        @visitor = Oracle.new Table.engine
+      end
+
+      describe 'Nodes::SelectStatement' do
+        describe 'limit' do
+          it 'adds a rownum clause' do
+            stmt = Nodes::SelectStatement.new
+            stmt.limit = 10
+            sql = @visitor.accept stmt
+            sql.should be_like %{ SELECT WHERE ROWNUM <= 10 }
+          end
+        end
+      end
+    end
+  end
+end