Ensure Contract#metadata is reliably orderable

This gets an annoyingly verbose comment, because otherwise it could be
removed and continue passing almost all the time.

Author: matthewd

activerecord/test/cases/relations_test.rb

@@ -2108,6 +2108,8 @@ def test_destroy_by
   test "joins with order by custom attribute" do
     companies = Company.create!([{ name: "test1" }, { name: "test2" }])
     companies.each { |company| company.contracts.create! }
+    # In ordering by Contract#metadata, we rely on that JSON string to
+    # be consistent
     assert_equal companies, Company.joins(:contracts).order(:metadata, :count)
     assert_equal companies.reverse, Company.joins(:contracts).order(metadata: :desc, count: :desc)
   end

activerecord/test/models/contract.rb

@@ -23,7 +23,11 @@ def bye
   end
 
   def update_metadata
-    self.metadata = { company_id: company_id, developer_id: developer_id }
+    # 'code' makes the JSON string consistently orderable, which is used
+    # by RelationsTest "joins with order by custom attribute". Without
+    # this it would still pass 99% of the time, but fail when two
+    # records' company_id lexical and numeric order differ (99, 100).
+    self.metadata = { code: company_id && "%08x" % company_id, company_id: company_id, developer_id: developer_id }
   end
 end