1 files changed, 24 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index bde31d1cda..88fd180fa5 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -2,6 +2,7 @@ require 'date'
 require 'bigdecimal'
 require 'bigdecimal/util'
 require 'active_support/core_ext/benchmark'
+require 'active_support/deprecation'
 
 # TODO: Autoload these files
 require 'active_record/connection_adapters/column'
@@ -38,6 +39,8 @@ module ActiveRecord
 
       define_callbacks :checkout, :checkin
 
+      attr_accessor :visitor
+
       def initialize(connection, logger = nil) #:nodoc:
         @active = nil
         @connection, @logger = connection, logger
@@ -45,6 +48,27 @@ module ActiveRecord
         @query_cache = Hash.new { |h,sql| h[sql] = {} }
         @open_transactions = 0
         @instrumenter = ActiveSupport::Notifications.instrumenter
+        @visitor = nil
+      end
+
+      # Returns a visitor instance for this adaptor, which conforms to the Arel::ToSql interface
+      def self.visitor_for(pool) # :nodoc:
+        adapter = pool.spec.config[:adapter]
+
+        if Arel::Visitors::VISITORS[adapter]
+          # TODO: Add a test for this
+
+          ActiveSupport::Deprecation.warn(
+            "Arel::Visitors::VISITORS is deprecated and will be removed. Database adapters " \
+            "should define a visitor_for method which returns the appropriate visitor for " \
+            "the database. For example, MysqlAdapter.visitor_for(pool) returns " \
+            "Arel::Visitors::MySQL.new(pool)."
+          )
+
+          Arel::Visitors::VISITORS[adapter].new(pool)
+        else
+          Arel::Visitors::ToSql.new(pool)
+        end
       end
 
       # Returns the human-readable name of the adapter. Use mixed case - one