Make it the responsibility of the connection to hold onto an ARel visitor for generating SQL. This improves the code architecture generally, and solves some problems with marshalling. Adapter authors please take note: you now need to define an Adapter.visitor_for method, but it degrades gracefully with a deprecation warning for now.

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