Added per-language configureable fallback setting

modeltrans/fields.py

@@ -97,11 +97,25 @@ def __get__(self, instance, instance_type=None):
 
         field_name = build_localized_fieldname(self.original_name, language)
 
-        # fallback if key does not exist, or contains the empty string (only for <original_field>_i18n fields)
-        if self.language is None and (field_name not in instance.i18n or not instance.i18n[field_name]):
-            return getattr(instance, self.original_name)
+        def has_field(field_name):
+            return field_name in instance.i18n and instance.i18n[field_name]
+
+        # in two cases, just return the value:
+        #  - if this is an explicit field (<name>_<lang>)
+        #  - if this is a implicit field (<name>_i18n) AND the value exists and is not Falsy
+        if self.language is not None or has_field(field_name):
+            return instance.i18n.get(field_name)
+
+        # this is the _i18n version of the field, and the current language is not available,
+        # so we walk the fallback chain:
+        for fallback_language in get_fallback_chain(language):
+            field_name = build_localized_fieldname(self.original_name, fallback_language)
 
-        return instance.i18n.get(field_name)
+            if has_field(field_name):
+                return instance.i18n.get(field_name)
+
+        # finally, return the original field if all else fails.
+        return getattr(instance, self.original_name)
 
     def __set__(self, instance, value):
         if instance.i18n is None:
@@ -156,6 +170,13 @@ def output_field(self):
 
         return Field()
 
+    def _localized_lookup(self, language):
+        if language == DEFAULT_LANGUAGE:
+            return self.original_name
+
+        name = build_localized_fieldname(self.original_name, language)
+        return RawSQL('{}.i18n->>%s'.format(self.model._meta.db_table), (name, ))
+
     def sql_lookup(self, fallback=True):
         '''
         Compose the sql lookup to get the value for this virtual field in a query.
@@ -165,13 +186,18 @@ def sql_lookup(self, fallback=True):
         if language == DEFAULT_LANGUAGE:
             return self.original_name
 
-        name = build_localized_fieldname(self.original_name, language)
-
-        i18n_lookup = RawSQL('{}.i18n->>%s'.format(self.model._meta.db_table), (name, ))
-
         if fallback:
-            return Coalesce(i18n_lookup, self.original_name, output_field=self.output_field())
+            fallback_chain = get_fallback_chain(language)
+            # first, add the current language to the list of lookups
+            lookups = [self._localized_lookup(language)]
+            # and now, add the list of fallback languages to the lookup list
+            for fallback_language in fallback_chain:
+                lookups.append(
+                    self._localized_lookup(fallback_language)
+                )
+            return Coalesce(*lookups, output_field=self.output_field())
         else:
+            i18n_lookup = self._localized_lookup(language)
             return Cast(i18n_lookup, self.output_field())
 
 

modeltrans/manager.py

@@ -63,6 +63,7 @@ class MultilingualQuerySet(models.query.QuerySet):
     When adding the `modeltrans.fields.TranslationField` to a model, MultilingualManager is automatically
     mixed in to the manager class of that model.
     '''
+
     def add_i18n_annotation(self, field, annotation_name=None, fallback=True):
         '''
         Private method to add an annotation to the query to extract the translated
@@ -203,8 +204,8 @@ def _filter_or_exclude(self, negate, *args, **kwargs):
         Examples:
             - `title_nl__contains='foo'` will add an annotation for `title_nl`
             - `title_nl='bar'` will add an annotation for `title_nl`
-            - `title_i18n='foo'` will add an annotation for `title_<language>`
-              where `<language>` is the current active language.
+            - `title_i18n='foo'` will add an annotation for a coalesce of the
+               current active language, and all items of the fallback chain.
             - `Q(title_nl__contains='foo') will add an annotation for `title_nl`
 
         In all cases, the field part of the field lookup will be changed to use

tests/test_models.py

@@ -3,7 +3,7 @@
 
 from django.core.exceptions import ValidationError
 from django.db import DataError, transaction
-from django.test import TestCase
+from django.test import TestCase, override_settings
 from django.utils.translation import override
 
 from tests.app.models import Blog, NullableTextModel, TextModel
@@ -202,14 +202,52 @@ def test_textfield(self):
         )
         self.assertEquals(m.description_nl, long_str)
 
+    @override_settings(
+        MODELTRANS_AVAILABLE_LANGUAGES=('fr', 'fy', 'nl'),
+        MODELTRANS_FALLBACK={
+            'default': ('en', ),
+            'fy': ('nl', 'en')
+        }
+    )
+    def test_fallback_chain(self):
+        '''
+        Testing the fallback chain setting for model
+        '''
+        b = Blog.objects.create(title='Buzzard', i18n={
+            'title_fy': 'Mûzefalk',
+            'title_nl': 'Buizerd',
+            'title_fr': 'Buse'
+        })
+
+        with override('nl'):
+            self.assertEquals(b.title_i18n, 'Buizerd')
+        with override('fr'):
+            self.assertEquals(b.title_i18n, 'Buse')
+        with override('fy'):
+            self.assertEquals(b.title_i18n, 'Mûzefalk')
+
+        b = Blog.objects.create(title='Buzzard', i18n={
+            'title_nl': 'Buizerd',
+            'title_fr': 'Buse'
+        })
+        with override('fy'):
+            self.assertEquals(b.title_i18n, 'Buizerd')
+
+        b = Blog.objects.create(title='Buzzard', i18n={
+            'title_fr': 'Buse'
+        })
+        with override('fy'):
+            self.assertEquals(b.title_i18n, 'Buzzard')
+        with override('fr'):
+            self.assertEquals(b.title_i18n, 'Buse')
+
 
 class RefreshFromDbTest(TestCase):
     def test_refresh_from_db(self):
         b = Blog.objects.create(title='Falcon', i18n={
             'title_nl': 'Valk',
             'title_de': 'Falk'
         })
-
         Blog.objects.filter(title='Falcon').update(title='Falcon II')
 
         b.refresh_from_db()