moving visitors around

lib/arel.rb

@@ -12,12 +12,7 @@
 require 'arel/expression'
 ####
 
-require 'arel/visitors/to_sql'
-require 'arel/visitors/postgresql'
-require 'arel/visitors/update_sql'
-require 'arel/visitors/join_sql'
-require 'arel/visitors/order_clauses'
-require 'arel/visitors/dot'
+require 'arel/visitors'
 
 require 'arel/tree_manager'
 require 'arel/insert_manager'

lib/arel/select_manager.rb

@@ -2,10 +2,11 @@ module Arel
   class SelectManager < Arel::TreeManager
     include Arel::Crud
 
-    def initialize engine
-      super
+    def initialize engine, table = nil
+      super(engine)
       @head   = Nodes::SelectStatement.new
       @ctx    = @head.cores.last
+      from table
     end
 
     def taken

lib/arel/table.rb

@@ -37,11 +37,11 @@ def alias
     end
 
     def tm
-      SelectManager.new(@engine).from(self)
+      SelectManager.new(@engine, self)
     end
 
     def from table
-      SelectManager.new(@engine).from table
+      SelectManager.new(@engine, table)
     end
 
     def joins manager

lib/arel/tree_manager.rb

@@ -4,23 +4,31 @@ class TreeManager
     include Arel::Relation
 
     VISITORS = {
-      'postgresql' => Arel::Visitors::PostgreSQL
+      'postgresql' => Arel::Visitors::PostgreSQL,
+      'mysql'      => Arel::Visitors::MySQL,
+      'mysql2'     => Arel::Visitors::MySQL,
     }
 
+    attr_accessor :visitor
+
     def initialize engine
-      @engine        = engine
-      @pool          = engine.connection_pool
-      @adapter       = @pool.spec.config[:adapter]
-      @visitor_klass = VISITORS[@adapter] || Visitors::ToSql
+      @engine  = engine
+      @visitor = nil
     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
-      viz = @visitor_klass.new @engine
-      viz.accept @head
+      visitor.accept @head
     end
 
     def initialize_copy other

lib/arel/update_manager.rb

@@ -46,11 +46,7 @@ def set values
     end
 
     def to_sql
-      viz = @visitor_klass.new @engine
-      unless @engine.connection_pool.spec.config[:adapter] =~ /^mysql/
-        viz.extend(Visitors::UpdateSql)
-      end
-      viz.accept @head
+      visitor.accept @head
     end
   end
 end

lib/arel/visitors.rb

+require 'arel/visitors/to_sql'
+require 'arel/visitors/postgresql'
+require 'arel/visitors/mysql'
+require 'arel/visitors/join_sql'
+require 'arel/visitors/order_clauses'
+require 'arel/visitors/dot'

lib/arel/visitors/update_sql.rb → lib/arel/visitors/mysql.rb

 module Arel
   module Visitors
-    module UpdateSql
+    class MySQL < Arel::Visitors::ToSql
       def visit_Arel_Nodes_UpdateStatement o
-        if o.orders.empty? && o.limit.nil?
-          wheres = o.wheres
-        else
-          stmt             = Nodes::SelectStatement.new
-          core             = stmt.cores.first
-          core.froms       = o.relation
-          core.projections = [o.relation.primary_key]
-          stmt.limit       = o.limit
-          stmt.orders      = o.orders
-
-          wheres = [Nodes::In.new(o.relation.primary_key, [stmt])]
-        end
-
         [
           "UPDATE #{visit o.relation}",
           ("SET #{o.values.map { |value| visit value }.join ', '}" unless o.values.empty?),
-          ("WHERE #{wheres.map { |x| visit x }.join ' AND '}" unless wheres.empty?)
+          ("WHERE #{o.wheres.map { |x| visit x }.join ' AND '}" unless o.wheres.empty?),
+          ("ORDER BY #{o.orders.map { |x| visit x }.join(', ')}" unless o.orders.empty?),
+          ("LIMIT #{o.limit}" if o.limit),
         ].compact.join ' '
       end
+
     end
   end
 end

lib/arel/visitors/to_sql.rb

@@ -22,15 +22,25 @@ def visit_Arel_Nodes_DeleteStatement o
       end
 
       def visit_Arel_Nodes_UpdateStatement o
+        if o.orders.empty? && o.limit.nil?
+          wheres = o.wheres
+        else
+          stmt             = Nodes::SelectStatement.new
+          core             = stmt.cores.first
+          core.froms       = o.relation
+          core.projections = [o.relation.primary_key]
+          stmt.limit       = o.limit
+          stmt.orders      = o.orders
+
+          wheres = [Nodes::In.new(o.relation.primary_key, [stmt])]
+        end
+
         [
           "UPDATE #{visit o.relation}",
           ("SET #{o.values.map { |value| visit value }.join ', '}" unless o.values.empty?),
-          ("WHERE #{o.wheres.map { |x| visit x }.join ' AND '}" unless o.wheres.empty?),
-          ("ORDER BY #{o.orders.map { |x| visit x }.join(', ')}" unless o.orders.empty?),
-          ("LIMIT #{o.limit}" if o.limit),
+          ("WHERE #{wheres.map { |x| visit x }.join ' AND '}" unless wheres.empty?)
         ].compact.join ' '
       end
-
       def visit_Arel_Nodes_InsertStatement o
         [
           "INSERT INTO #{visit o.relation}",