Add unique constraint to Translation

To make sure only one translation per article is possible.

lib/outlook/translations/translation.ex

@@ -26,5 +26,8 @@ defmodule Outlook.Translations.Translation do
     |> cast(attrs, [:lang, :title, :teaser, :date, :public, :unauthorized])
     |> cast(attrs, [:content], force_changes: true)
     |> validate_required([:lang, :title, :teaser, :content, :date, :public, :unauthorized])
+    |> unique_constraint([:lang, :article_id],
+        message: "translation for this language already exists",
+        name: :article_id_lang_unique_index)
   end
 end

priv/repo/migrations/20221230170041_add_lang_article_id_unique_index_to_translations.exs

@@ -0,0 +1,7 @@
+defmodule Outlook.Repo.Migrations.AddLangArticleIdUniqueIndexToTranslations do
+  use Ecto.Migration
+
+  def change do
+    create unique_index(:translations, [:article_id, :lang], name: :article_id_lang_unique_index)
+  end
+end