Make sure Model#active_relation always adds STI conditions if needed

activerecord/lib/active_record/base.rb

@@ -872,7 +872,6 @@ module ActiveRecord #:nodoc:
         relation = active_relation
 
         relation = relation.where(conditions) if conditions
-        relation = relation.where(type_condition) if finder_needs_type_condition?
         relation = relation.limit(options[:limit]) if options[:limit].present?
         relation = relation.order(options[:order]) if options[:order].present?
 
@@ -1389,7 +1388,7 @@ module ActiveRecord #:nodoc:
       def reset_column_information
         undefine_attribute_methods
         @column_names = @columns = @columns_hash = @content_columns = @dynamic_methods_hash = @inheritance_column = nil
-        @active_relation = @arel_engine = nil
+        @arel_engine = @active_relation = @arel_engine = nil
       end
 
       def reset_column_information_and_inheritable_attributes_for_all_subclasses#:nodoc:
@@ -1504,6 +1503,7 @@ module ActiveRecord #:nodoc:
 
       def active_relation
         @active_relation ||= Relation.new(self, arel_table)
+        finder_needs_type_condition? ? @active_relation.where(type_condition) : @active_relation
       end
 
       def arel_table(table_name_alias = nil)
@@ -1564,7 +1564,6 @@ module ActiveRecord #:nodoc:
 
         def construct_finder_arel(options = {}, scope = nil)
           relation = active_relation.apply_finder_options(options)
-          relation = relation.where(type_condition) if finder_needs_type_condition?
           relation = scope.merge(relation) if scope
           relation
         end

activerecord/lib/active_record/calculations.rb

@@ -167,8 +167,6 @@ module ActiveRecord
 
             if merge_with_relation
               relation = merge_with_relation.except(:select, :order, :limit, :offset, :group, :from).merge(relation)
-            else
-              relation = relation.where(type_condition) if finder_needs_type_condition?
             end
 
             from = merge_with_relation.from_value if merge_with_relation && merge_with_relation.from_value.present?
@@ -194,8 +192,6 @@ module ActiveRecord
             relation.where_values = merge_with_relation.where_values
 
             merge_limit = merge_with_relation.taken
-          else
-            relation = relation.where(type_condition) if finder_needs_type_condition?
           end
 
           relation = relation.apply_finder_options(options.slice(:joins, :group, :having, :order, :conditions, :from)).

activerecord/lib/active_record/named_scope.rb

@@ -29,7 +29,7 @@ module ActiveRecord
           current_scope = current_scoped_methods
 
           unless current_scope
-            finder_needs_type_condition? ? active_relation.where(type_condition) : active_relation.spawn
+            active_relation.spawn
           else
             construct_finder_arel({}, current_scoped_methods)
           end

activerecord/lib/active_record/relation/spawn_methods.rb

@@ -94,7 +94,9 @@ module ActiveRecord
     def apply_finder_options(options)
       options.assert_valid_keys(VALID_FIND_OPTIONS)
 
-      relation = joins(options[:joins]).
+      relation = spawn
+
+      relation = relation.joins(options[:joins]).
         where(options[:conditions]).
         select(options[:select]).
         group(options[:group]).