3 files changed, 23 insertions, 2 deletions
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 5c7c0feeb7..5a5139256d 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -276,11 +276,11 @@ module ActiveRecord
     #   User.new(first_name: 'Jamie')
     def initialize(attributes = nil, options = {})
       @attributes = self.class._default_attributes.dup
+      self.class.define_attribute_methods
 
       init_internals
       initialize_internals_callback
 
-      self.class.define_attribute_methods
       # +options+ argument is only needed to make protected_attributes gem easier to hook.
       # Remove it when we drop support to this gem.
       init_attributes(attributes, options) if attributes
diff --git a/activerecord/lib/active_record/transactions.rb b/activerecord/lib/active_record/transactions.rb
index 1c48196762..9cef50029b 100644
--- a/activerecord/lib/active_record/transactions.rb
+++ b/activerecord/lib/active_record/transactions.rb
@@ -378,7 +378,7 @@ module ActiveRecord
           thaw unless restore_state[:frozen?]
           @new_record = restore_state[:new_record]
           @destroyed  = restore_state[:destroyed]
-          write_attribute(self.class.primary_key, restore_state[:id])
+          write_attribute(self.class.primary_key, restore_state[:id]) if self.class.primary_key
         end
       end
     end
diff --git a/activerecord/test/cases/transactions_test.rb b/activerecord/test/cases/transactions_test.rb
index 27a7c9212b..d1d8e71c34 100644
--- a/activerecord/test/cases/transactions_test.rb
+++ b/activerecord/test/cases/transactions_test.rb
@@ -650,6 +650,27 @@ class TransactionTest < ActiveRecord::TestCase
     assert transaction.state.committed?
   end
 
+  def test_transaction_rollback_with_primarykeyless_tables
+    connection = ActiveRecord::Base.connection
+    connection.create_table(:transaction_without_primary_keys, force: true, id: false) do |t|
+       t.integer :thing_id
+    end
+
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = 'transaction_without_primary_keys'
+      after_commit { } # necessary to trigger the has_transactional_callbacks branch
+    end
+
+    assert_no_difference(-> { klass.count }) do
+      ActiveRecord::Base.transaction do
+        klass.create!
+        raise ActiveRecord::Rollback
+      end
+    end
+  ensure
+    connection.execute("DROP TABLE IF EXISTS transaction_without_primary_keys")
+  end
+
   private
 
   %w(validation save destroy).each do |filter|