Set up delegations also for to_a and arel branches.

activerecord/lib/active_record/relation.rb

@@ -132,13 +132,6 @@ module ActiveRecord
       first || new(attributes, options, &block)
     end
 
-    def respond_to?(method, include_private = false)
-      arel.respond_to?(method, include_private)     ||
-        Array.method_defined?(method)               ||
-        @klass.respond_to?(method, include_private) ||
-        super
-    end
-
     # Runs EXPLAIN on the query or queries triggered by this relation and
     # returns the result as a string. The string is formatted imitating the
     # ones printed by the database shell.

activerecord/lib/active_record/relation/delegation.rb

@@ -2,9 +2,8 @@ require 'active_support/core_ext/module/delegation'
 
 module ActiveRecord
   module Delegation
-    # These are explicitly delegated to improve performance (avoids method_missing)
+    # Set up common delegations for performance (avoids method_missing)
     delegate :to_xml, :to_yaml, :length, :collect, :map, :each, :all?, :include?, :to_ary, :to => :to_a
-    delegate :ast, :engine, :to => :arel
     delegate :table_name, :quoted_table_name, :primary_key, :quoted_primary_key,
              :connection, :columns_hash, :auto_explain_threshold_in_seconds, :to => :klass
 
@@ -24,15 +23,23 @@ module ActiveRecord
       end
     end
 
+    def respond_to?(method, include_private = false)
+      super || Array.method_defined?(method) ||
+        @klass.respond_to?(method, include_private) ||
+        arel.respond_to?(method, include_private)
+    end
+
     protected
 
     def method_missing(method, *args, &block)
       if Array.method_defined?(method)
+        ::ActiveRecord::Delegation.delegate method, :to => :to_a
         to_a.send(method, *args, &block)
       elsif @klass.respond_to?(method)
         ::ActiveRecord::Delegation.delegate_to_scoped_klass(method)
         scoping { @klass.send(method, *args, &block) }
       elsif arel.respond_to?(method)
+        ::ActiveRecord::Delegation.delegate method, :to => :arel
         arel.send(method, *args, &block)
       else
         super