Fix possible doubling of contact objects after race

db/migrate/20200622080240_add_unique_constraints_to_domain_objects.rb

@@ -0,0 +1,25 @@
+class AddUniqueConstraintsToDomainObjects < ActiveRecord::Migration[6.0]
+  def up
+    execute <<-SQL
+      alter table domain_contacts
+        add constraint uniq_contact_of_type_per_domain unique (domain_id, type, contact_id);
+    SQL
+
+    execute <<-SQL
+      alter table nameservers
+        add constraint uniq_hostname_per_domain unique (domain_id, hostname);
+    SQL
+  end
+
+  def down
+    execute <<-SQL
+      alter table domain_contacts
+        drop constraint if exists uniq_contact_of_type_per_domain;
+    SQL
+
+    execute <<-SQL
+      alter table nameservers
+        drop constraint if exists uniq_hostname_per_domain;
+    SQL
+  end
+end

test/models/contact_test.rb

@@ -177,7 +177,7 @@ class ContactTest < ActiveSupport::TestCase
 
   def test_linked_when_in_use_as_domain_contact
     Domain.update_all(registrant_id: contacts(:william).id)
-    DomainContact.update_all(contact_id: @contact.id)
+    DomainContact.first.update(contact_id: @contact.id)
 
     assert @contact.linked?
   end

test/models/domain_test.rb

@@ -137,9 +137,9 @@ class DomainTest < ActiveSupport::TestCase
     contact = contacts(:john)
 
     domain.admin_contacts << contact
-    domain.admin_contacts << contact
-
-    assert domain.invalid?
+    assert_raise ActiveRecord::RecordNotUnique do
+      domain.admin_contacts << contact
+    end
   end
 
   def test_invalid_when_the_same_tech_contact_is_linked_twice
@@ -147,9 +147,9 @@ class DomainTest < ActiveSupport::TestCase
     contact = contacts(:john)
 
     domain.tech_contacts << contact
-    domain.tech_contacts << contact
-
-    assert domain.invalid?
+    assert_raise ActiveRecord::RecordNotUnique do
+      domain.tech_contacts << contact
+    end
   end
 
   def test_validates_name_server_count_when_name_servers_are_required