ARel only requires the connection from the AR class. Simply return the AR class rather than jump through hoops and store ivars

activerecord/lib/active_record/base.rb

@@ -747,7 +747,7 @@ module ActiveRecord #:nodoc:
         undefine_attribute_methods
         reset_column_cache
         @column_names = @content_columns = @dynamic_methods_hash = @inheritance_column = nil
-        @arel_engine = @relation = nil
+        @relation = nil
       end
 
       def reset_column_cache # :nodoc:
@@ -856,13 +856,7 @@ module ActiveRecord #:nodoc:
       end
 
       def arel_engine
-        @arel_engine ||= begin
-          if self == ActiveRecord::Base
-            ActiveRecord::Base
-          else
-            connection_handler.connection_pools[name] ? self : superclass.arel_engine
-          end
-        end
+        self
       end
 
       # Returns a scope for this class without taking into account the default_scope.

activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb

@@ -50,34 +50,34 @@ module ActiveRecord
     # may be returned on an error.
     def self.establish_connection(spec = nil)
       case spec
-        when nil
-          raise AdapterNotSpecified unless defined?(Rails.env)
-          establish_connection(Rails.env)
-        when ConnectionSpecification
-          self.connection_handler.establish_connection(name, spec)
-        when Symbol, String
-          if configuration = configurations[spec.to_s]
-            establish_connection(configuration)
-          else
-            raise AdapterNotSpecified, "#{spec} database is not configured"
-          end
+      when nil
+        raise AdapterNotSpecified unless defined?(Rails.env)
+        establish_connection(Rails.env)
+      when ConnectionSpecification
+        self.connection_handler.establish_connection(name, spec)
+      when Symbol, String
+        if configuration = configurations[spec.to_s]
+          establish_connection(configuration)
         else
-          spec = spec.symbolize_keys
-          unless spec.key?(:adapter) then raise AdapterNotSpecified, "database configuration does not specify adapter" end
+          raise AdapterNotSpecified, "#{spec} database is not configured"
+        end
+      else
+        spec = spec.symbolize_keys
+        unless spec.key?(:adapter) then raise AdapterNotSpecified, "database configuration does not specify adapter" end
 
-          begin
-            require "active_record/connection_adapters/#{spec[:adapter]}_adapter"
-          rescue LoadError => e
-            raise "Please install the #{spec[:adapter]} adapter: `gem install activerecord-#{spec[:adapter]}-adapter` (#{e})"
-          end
+        begin
+          require "active_record/connection_adapters/#{spec[:adapter]}_adapter"
+        rescue LoadError => e
+          raise "Please install the #{spec[:adapter]} adapter: `gem install activerecord-#{spec[:adapter]}-adapter` (#{e})"
+        end
 
-          adapter_method = "#{spec[:adapter]}_connection"
-          unless respond_to?(adapter_method)
-            raise AdapterNotFound, "database configuration specifies nonexistent #{spec[:adapter]} adapter"
-          end
+        adapter_method = "#{spec[:adapter]}_connection"
+        unless respond_to?(adapter_method)
+          raise AdapterNotFound, "database configuration specifies nonexistent #{spec[:adapter]} adapter"
+        end
 
-          remove_connection
-          establish_connection(ConnectionSpecification.new(spec, adapter_method))
+        remove_connection
+        establish_connection(ConnectionSpecification.new(spec, adapter_method))
       end
     end
 

activerecord/test/cases/multiple_db_test.rb

@@ -84,8 +84,8 @@ class MultipleDbTest < ActiveRecord::TestCase
     assert_equal "Ruby Developer", Entrant.find(1).name
   end
 
-  def test_arel_table_engines
-    assert_not_equal Entrant.arel_engine, Course.arel_engine
-    assert_equal Entrant.arel_engine, Bird.arel_engine
+  def test_connections
+    assert_not_equal Entrant.connection, Course.connection
+    assert_equal Entrant.connection, Bird.connection
   end
 end