caching visitor on a per engine basis

2 files changed, 22 insertions, 15 deletions

diff --git a/lib/arel/tree_manager.rb b/lib/arel/tree_manager.rb
index fb5037cd9f..8a13345c91 100644
--- a/lib/arel/tree_manager.rb
+++ b/lib/arel/tree_manager.rb
@@ -3,30 +3,17 @@ module Arel
     # FIXME: Remove this.
     include Arel::Relation
 
-    VISITORS = {
-      'postgresql' => Arel::Visitors::PostgreSQL,
-      'mysql'      => Arel::Visitors::MySQL,
-      'mysql2'     => Arel::Visitors::MySQL,
-    }
-
-    attr_writer :visitor
+    attr_accessor :visitor
 
     def initialize engine
       @engine  = engine
-      @visitor = nil
+      @visitor = Visitors.visitor_for @engine
     end
 
     def to_dot
       Visitors::Dot.new.accept @head
     end
 
-    def visitor
-      return @visitor if @visitor
-      pool          = @engine.connection_pool
-      adapter       = pool.spec.config[:adapter]
-      @visitor = (VISITORS[adapter] || Visitors::ToSql).new(@engine)
-    end
-
     def to_sql
       visitor.accept @head
     end
diff --git a/lib/arel/visitors.rb b/lib/arel/visitors.rb
index 22077d5943..879635575b 100644
--- a/lib/arel/visitors.rb
+++ b/lib/arel/visitors.rb
@@ -4,3 +4,23 @@ require 'arel/visitors/mysql'
 require 'arel/visitors/join_sql'
 require 'arel/visitors/order_clauses'
 require 'arel/visitors/dot'
+
+module Arel
+  module Visitors
+    VISITORS = {
+      'postgresql' => Arel::Visitors::PostgreSQL,
+      'mysql'      => Arel::Visitors::MySQL,
+      'mysql2'     => Arel::Visitors::MySQL,
+    }
+
+    ENGINE_VISITORS = Hash.new do |hash, engine|
+      pool         = engine.connection_pool
+      adapter      = pool.spec.config[:adapter]
+      hash[engine] = (VISITORS[adapter] || Visitors::ToSql).new(engine)
+    end
+
+    def self.visitor_for engine
+      ENGINE_VISITORS[engine]
+    end
+  end
+end