Tolerate composite primary keys

lib/super_diff/active_record/monkey_patches.rb

@@ -4,11 +4,12 @@
 class ActiveRecord::Base
   # TODO: Remove this monkey patch if possible
   def attributes_for_super_diff
-    id_attr = self.class.primary_key
+    id_attrs = Array(self.class.primary_key).compact
+    other_attrs = attributes.keys.sort - id_attrs
+    attributes_to_hash = ->(keys, hash) { keys.reduce(hash) { |memo, key| memo.merge(key.to_sym => attributes[key]) } }
 
-    (attributes.keys.sort - [id_attr]).reduce(
-      id_attr.nil? ? {} : { id_attr.to_sym => id }
-    ) { |hash, key| hash.merge(key.to_sym => attributes[key]) }
+    attributes_to_hash.call(id_attrs, {})
+                      .then { |result| attributes_to_hash.call(other_attrs, result) }
   end
 end
 # rubocop:enable Style/ClassAndModuleChildren

spec/support/models/active_record.rb

@@ -8,6 +8,7 @@ def self.define_tables
           SuperDiff::Test::Models::ActiveRecord::Person.define_table
           SuperDiff::Test::Models::ActiveRecord::ShippingAddress.define_table
           SuperDiff::Test::Models::ActiveRecord::TimeSeriesData.define_table
+          SuperDiff::Test::Models::ActiveRecord::Order.define_table
         end
       end
     end

spec/support/models/active_record/order.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+module SuperDiff
+  module Test
+    module Models
+      module ActiveRecord
+        class Order < ::ActiveRecord::Base
+          def self.define_table
+            ::ActiveRecord::Base
+              .connection
+              .create_table(
+                :orders,
+                force: true,
+                primary_key: %i[store_id sku]
+              ) do |t|
+              t.integer :latest_outcome, null: false
+              t.string :details
+              t.integer :store_id, null: false
+              t.string :sku, null: false
+            end
+          end
+        end
+      end
+    end
+  end
+end

spec/support/shared_examples/active_record.rb

@@ -103,6 +103,50 @@
       end
     end
 
+    context 'when comparing two instances of an ActiveRecord model that has a composite primary key' do
+      it 'produces the correct output' do
+        as_both_colored_and_uncolored do |color_enabled|
+          snippet = <<~TEST.strip
+            actual = SuperDiff::Test::Models::ActiveRecord::Order.new(
+              store_id: 456,
+              sku: 'hi',
+              latest_outcome: 1,
+            )
+            expected = SuperDiff::Test::Models::ActiveRecord::Order.new(
+              store_id: 123,
+              sku: 'hello',
+              latest_outcome: 2,
+            )
+            expect(actual).to eq(expected)
+          TEST
+          program = make_program(snippet, color_enabled: color_enabled)
+
+          expected_output =
+            build_expected_output(
+              color_enabled: color_enabled,
+              snippet: 'expect(actual).to eq(expected)',
+              newline_before_expectation: true,
+              expectation:
+                proc do
+                  line do
+                    plain 'Expected '
+                    actual %(#<SuperDiff::Test::Models::ActiveRecord::Order ["store_id", "sku"]: [456, "hi"], details: nil, latest_outcome: 1, sku: "hi", store_id: 456>)
+                  end
+
+                  line do
+                    plain '   to eq '
+                    expected %(#<SuperDiff::Test::Models::ActiveRecord::Order ["store_id", "sku"]: [123, "hello"], details: nil, latest_outcome: 2, sku: "hello", store_id: 123>)
+                  end
+                end
+            )
+
+          expect(program).to produce_output_when_run(expected_output).in_color(
+            color_enabled
+          )
+        end
+      end
+    end
+
     context 'when comparing instances of two different ActiveRecord models' do
       it 'produces the correct output' do
         as_both_colored_and_uncolored do |color_enabled|