1 files changed, 45 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/associations/has_one_through_association.rb b/activerecord/lib/active_record/associations/has_one_through_association.rb
new file mode 100644
index 0000000000..10978b2d93
--- /dev/null
+++ b/activerecord/lib/active_record/associations/has_one_through_association.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module Associations
+    # = Active Record Has One Through Association
+    class HasOneThroughAssociation < HasOneAssociation #:nodoc:
+      include ThroughAssociation
+
+      private
+        def replace(record, save = true)
+          create_through_record(record, save)
+          self.target = record
+        end
+
+        def create_through_record(record, save)
+          ensure_not_nested
+
+          through_proxy  = through_association
+          through_record = through_proxy.load_target
+
+          if through_record && !record
+            through_record.destroy
+          elsif record
+            attributes = construct_join_attributes(record)
+
+            if through_record && through_record.destroyed?
+              through_record = through_proxy.tap(&:reload).target
+            end
+
+            if through_record
+              if through_record.new_record?
+                through_record.assign_attributes(attributes)
+              else
+                through_record.update(attributes)
+              end
+            elsif owner.new_record? || !save
+              through_proxy.build(attributes)
+            else
+              through_proxy.create(attributes)
+            end
+          end
+        end
+    end
+  end
+end