Add method to retrieve translations in one database query

This methods performs much better when we need to load a lot of
globalized models translations and returns the best fallback translation
for the current language.

app/models/concerns/globalizable.rb

@@ -100,5 +100,22 @@ module Globalizable
     def translation_class_delegate(method)
       translation_class.instance_eval { delegate method, to: :globalized_model }
     end
+
+    def with_fallback_translation
+      translations_foreign_key = reflect_on_association(:translations).foreign_key
+      fallbacks = Globalize.fallbacks(Globalize.locale)
+
+      fallbacks_with_order = fallbacks.map.with_index do |locale, order|
+        "('#{locale}', #{order})"
+      end.join(", ")
+
+      translations_ids = translation_class
+        .select("DISTINCT ON (#{translations_foreign_key}) id")
+        .where(locale: fallbacks)
+        .joins("LEFT JOIN (VALUES #{fallbacks_with_order}) AS locales(name, ordering) ON locale = locales.name")
+        .order(translations_foreign_key, "locales.ordering")
+
+      with_translations(fallbacks).where("#{translations_table_name}.id": translations_ids)
+    end
   end
 end

spec/models/concerns/globalizable.rb

@@ -15,10 +15,7 @@ shared_examples_for "globalizable" do |factory_name|
   before do
     record.update!(attribute => "In English")
 
-    I18n.with_locale(:es) do
-      record.update!(required_fields.index_with("En español"))
-      record.update!(attribute => "En español")
-    end
+    add_translation(record, :es, "En español")
 
     record.reload
   end
@@ -98,7 +95,7 @@ shared_examples_for "globalizable" do |factory_name|
     end
 
     it "Does not automatically add a translation for the current locale" do
-      record.translations.find_by(locale: :en).destroy!
+      destroy_translation(record, :en)
       record.reload
 
       record.update!(translations_attributes: [
@@ -188,4 +185,62 @@ shared_examples_for "globalizable" do |factory_name|
       expect(record.send(attribute)).to eq "Deutsche Sprache"
     end
   end
+
+  describe ".with_fallback_translation" do
+    before do
+      fallbacks = { fr: %i[fr en es], es: %i[es fr en], en: %i[en es fr] }
+      allow(I18n).to receive(:fallbacks).and_return(I18n.fallbacks.merge(fallbacks))
+      Globalize.set_fallbacks_to_all_available_locales
+    end
+
+    it "returns records with the best fallback translation available for the current locale" do
+      record.update!(attribute => "Content in English")
+      add_translation(record, :es, "Contenido en español")
+      add_translation(record, :fr, "Contenu en français")
+
+      I18n.with_locale(:es) do
+        expect(attribute_with_fallback_translation(record, attribute)).to eq "Contenido en español"
+
+        destroy_translation(record, :es)
+
+        expect(attribute_with_fallback_translation(record, attribute)).to eq "Contenu en français"
+
+        destroy_translation(record, :fr)
+
+        expect(attribute_with_fallback_translation(record, attribute)).to eq "Content in English"
+      end
+
+      record.reload
+
+      add_translation(record, :es, "Contenido en español")
+      add_translation(record, :fr, "Contenu en français")
+
+      I18n.with_locale(:fr) do
+        expect(attribute_with_fallback_translation(record, attribute)).to eq "Contenu en français"
+
+        destroy_translation(record, :fr)
+
+        expect(attribute_with_fallback_translation(record, attribute)).to eq "Content in English"
+
+        destroy_translation(record, :en)
+
+        expect(attribute_with_fallback_translation(record, attribute)).to eq "Contenido en español"
+      end
+    end
+  end
+end
+
+def add_translation(record, locale, text)
+  I18n.with_locale(locale) do
+    record.update!(required_fields.index_with(text))
+    record.update!(attribute => text)
+  end
+end
+
+def destroy_translation(record, locale)
+  record.translations.find_by(locale: locale).destroy!
+end
+
+def attribute_with_fallback_translation(record, attribute)
+  record.class.with_fallback_translation.where(id: record.id).pick(attribute)
 end