Don't rely on the internal representation of join values

I'm going to be extracting this logic into a clause class, things need
to go through a method and not access the values hash directly.

2 files changed, 6 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/associations/preloader.rb b/activerecord/lib/active_record/associations/preloader.rb
index c3e49007ea..97f4bd3811 100644
--- a/activerecord/lib/active_record/associations/preloader.rb
+++ b/activerecord/lib/active_record/associations/preloader.rb
@@ -89,7 +89,7 @@ module ActiveRecord
       #   { author: :avatar }
       #   [ :books, { author: :avatar } ]
 
-      NULL_RELATION = Struct.new(:values, :where_clause).new({}, Relation::WhereClause.empty)
+      NULL_RELATION = Struct.new(:values, :where_clause, :joins_values).new({}, Relation::WhereClause.empty, [])
 
       def preload(records, associations, preload_scope = nil)
         records       = Array.wrap(records).compact.uniq
diff --git a/activerecord/lib/active_record/associations/preloader/association.rb b/activerecord/lib/active_record/associations/preloader/association.rb
index 23848f5e54..9e4a2b925c 100644
--- a/activerecord/lib/active_record/associations/preloader/association.rb
+++ b/activerecord/lib/active_record/associations/preloader/association.rb
@@ -139,7 +139,11 @@ module ActiveRecord
 
           scope._select! preload_values[:select] || values[:select] || table[Arel.star]
           scope.includes! preload_values[:includes] || values[:includes]
-          scope.joins! preload_values[:joins] || values[:joins]
+          if preload_scope.joins_values.any?
+            scope.joins!(preload_scope.joins_values)
+          else
+            scope.joins!(reflection_scope.joins_values)
+          end
           scope.order! preload_values[:order] || values[:order]
 
           if preload_values[:readonly] || values[:readonly]