Support composite primary key in AR::Base#to_param

Author: nvasilevski

activerecord/lib/active_record/base.rb

@@ -331,6 +331,8 @@ class Base
     include Suppressor
     include Normalization
     include Marshalling::Methods
+
+    self.param_delimiter = "_"
   end
 
   ActiveSupport.run_load_hooks(:active_record, Base)

activerecord/lib/active_record/integration.rb

@@ -55,8 +55,8 @@ module Integration
     #   user = User.find_by(name: 'Phusion')
     #   user_path(user)  # => "/users/Phusion"
     def to_param
-      # We can't use alias_method here, because method 'id' optimizes itself on the fly.
-      id && id.to_s # Be sure to stringify the id for routes
+      return unless id
+      Array(id).join(self.class.param_delimiter)
     end
 
     # Returns a stable cache key that can be used to identify this record.

activerecord/test/cases/integration_test.rb

@@ -6,6 +6,7 @@
 require "models/computer"
 require "models/owner"
 require "models/pet"
+require "models/cpk"
 
 class IntegrationTest < ActiveRecord::TestCase
   fixtures :companies, :developers, :owners, :pets
@@ -97,6 +98,32 @@ def test_to_param_with_no_arguments
     assert_equal "Firm", Firm.to_param
   end
 
+  def test_to_param_for_a_composite_primary_key_model
+    assert_equal "1_123", Cpk::Order.new(id: [1, 123]).to_param
+  end
+
+  def test_param_delimiter_changes_delimiter_used_in_to_param
+    old_delimiter = Cpk::Order.param_delimiter
+    Cpk::Order.param_delimiter = ","
+    assert_equal("1,123", Cpk::Order.new(id: [1, 123]).to_param)
+  ensure
+    Cpk::Order.param_delimiter = old_delimiter
+  end
+
+  def test_param_delimiter_is_defined_per_class
+    old_order_delimiter = Cpk::Order.param_delimiter
+    old_book_delimiter = Cpk::Book.param_delimiter
+
+    Cpk::Order.param_delimiter = ","
+    Cpk::Book.param_delimiter = ";"
+
+    assert_equal("1,123", Cpk::Order.new(id: [1, 123]).to_param)
+    assert_equal("1;123", Cpk::Book.new(id: [1, 123]).to_param)
+  ensure
+    Cpk::Order.param_delimiter = old_order_delimiter
+    Cpk::Order.param_delimiter = old_book_delimiter
+  end
+
   def test_cache_key_for_existing_record_is_not_timezone_dependent
     utc_key = Developer.first.cache_key