Don't error when `dup`ing a record with no PK

3 files changed, 19 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/attribute_set.rb b/activerecord/lib/active_record/attribute_set.rb
index 8a964fb03c..df4fd31e08 100644
--- a/activerecord/lib/active_record/attribute_set.rb
+++ b/activerecord/lib/active_record/attribute_set.rb
@@ -52,6 +52,12 @@ module ActiveRecord
       super
     end
 
+    def reset(key)
+      if include?(key)
+        write_from_database(key, nil)
+      end
+    end
+
     protected
 
     attr_reader :attributes
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 224112b559..30b8485c8b 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -315,9 +315,8 @@ module ActiveRecord
 
     ##
     def initialize_dup(other) # :nodoc:
-      pk = self.class.primary_key
       @attributes = @attributes.dup
-      @attributes.write_from_database(pk, nil)
+      @attributes.reset(self.class.primary_key)
 
       run_callbacks(:initialize) unless _initialize_callbacks.empty?
 
diff --git a/activerecord/test/cases/dup_test.rb b/activerecord/test/cases/dup_test.rb
index 409d9a82e2..638cffe0e6 100644
--- a/activerecord/test/cases/dup_test.rb
+++ b/activerecord/test/cases/dup_test.rb
@@ -141,5 +141,17 @@ module ActiveRecord
     ensure
       Topic.default_scopes = prev_default_scopes
     end
+
+    def test_dup_without_primary_key
+      klass = Class.new(ActiveRecord::Base) do
+        self.table_name = 'parrots_pirates'
+      end
+
+      record = klass.create!
+
+      assert_nothing_raised do
+        record.dup
+      end
+    end
   end
 end