Fix collection= on hm:t join models when unsaved

If assigning to a has_many :through collection against an unsaved
object using the collection=[<array_of_items>] syntax, the join models
were not properly created, previously.

1 files changed, 14 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index 88ff11f953..d8f14c896c 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -37,6 +37,20 @@ module ActiveRecord
         super
       end
 
+      def concat_records(records)
+        ensure_not_nested
+
+        records = super
+
+        if owner.new_record? && records
+          records.flatten.each do |record|
+            build_through_record(record)
+          end
+        end
+
+        records
+      end
+
       def insert_record(record, validate = true, raise = false)
         ensure_not_nested