From 851fb27ae3a70a9c41e9345b520af2a17c9d51d0 Mon Sep 17 00:00:00 2001
From: Nikita Vasilevsky <nikita.vasilevsky@shopify.com>
Date: Wed, 5 Apr 2023 17:32:59 +0000
Subject: [PATCH] Reset composite primary key in `#dup`

This commit ensures that the composite primary key is reset when
`#dup` is called on an instance of an `ActiveRecord::Base` subclass.

For example:

```ruby
class TravelRoute < ActiveRecord::Base
  self.primary_key = [:origin, :destination]
end

route = TravelRoute.new(origin: "NYC", destination: "LAX")
route.dup # => #<TravelRoute origin: nil, destination: nil>
```
---
 activerecord/lib/active_record/core.rb |  6 +++++-
 activerecord/test/cases/base_test.rb   | 14 +++++++++++++-
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 72d72a7325..d90b284e58 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -507,7 +507,11 @@ def init_with_attributes(attributes, new_record = false) # :nodoc:
     ##
     def initialize_dup(other) # :nodoc:
       @attributes = @attributes.deep_dup
-      @attributes.reset(@primary_key)
+      if self.class.composite_primary_key?
+        @primary_key.each { |key| @attributes.reset(key) }
+      else
+        @attributes.reset(@primary_key)
+      end
 
       _run_initialize_callbacks
 
diff --git a/activerecord/test/cases/base_test.rb b/activerecord/test/cases/base_test.rb
index a3ba41244d..2df0447d04 100644
--- a/activerecord/test/cases/base_test.rb
+++ b/activerecord/test/cases/base_test.rb
@@ -28,6 +28,7 @@
 require "models/bulb"
 require "models/pet"
 require "models/owner"
+require "models/cpk/book"
 require "concurrent/atomic/count_down_latch"
 require "active_support/core_ext/enumerable"
 require "active_support/core_ext/kernel/reporting"
@@ -101,7 +102,9 @@ def setup
 end
 
 class BasicsTest < ActiveRecord::TestCase
-  fixtures :topics, :companies, :developers, :projects, :computers, :accounts, :minimalistics, "warehouse-things", :authors, :author_addresses, :categorizations, :categories, :posts
+  fixtures :topics, :companies, :developers, :projects, :computers, :accounts,
+    :minimalistics, "warehouse-things", :authors, :author_addresses, :categorizations, :categories,
+    :posts, :cpk_books
 
   def test_generated_association_methods_module_name
     mod = Post.send(:generated_association_methods)
@@ -1002,6 +1005,15 @@ def test_dup
     assert_equal("c", duped_topic.title)
   end
 
+  def test_dup_for_a_composite_primary_key_model
+    book = cpk_books(:cpk_great_author_first_book)
+    new_book = book.dup
+
+    assert_equal "The first book", new_book.title
+    assert_nil new_book.author_id
+    assert_nil new_book.number
+  end
+
   DeveloperSalary = Struct.new(:amount)
   def test_dup_with_aggregate_of_same_name_as_attribute
     developer_with_aggregate = Class.new(ActiveRecord::Base) do