feat: Support language-specific field defaults

Refs #700, #698

modeltranslation/fields.py

@@ -4,6 +4,8 @@
 from django import VERSION, forms
 from django.core.exceptions import ImproperlyConfigured
 from django.db.models import fields
+from django.utils.encoding import force_str
+from django.utils.translation import override
 
 from modeltranslation import settings as mt_settings
 from modeltranslation.thread_context import fallbacks_enabled
@@ -256,6 +258,17 @@ def __ne__(self, other):
     def __hash__(self):
         return hash((self.creation_counter, self.language))
 
+    def get_default(self):
+        with override(self.language):
+            default = super().get_default()
+            # we must *force evaluation* at this point, otherwise the lazy translatable
+            # string is returned and will be evaluated only later when the main language
+            # is activated again (because this context block has exited).
+            #
+            # force_str passes protected types as-is, which includes None, int, float,
+            # datetime...
+            return force_str(default, strings_only=True)
+
     def formfield(self, *args, **kwargs):
         """
         Returns proper formfield, according to empty_values setting

modeltranslation/tests/migrations/0001_initial.py

@@ -1,4 +1,4 @@
-# Generated by Django 3.2.20 on 2023-09-04 07:33
+# Generated by Django 3.2.21 on 2023-09-05 02:55
 
 import django.contrib.auth.models
 import django.core.validators
@@ -625,6 +625,15 @@ class Migration(migrations.Migration):
                 ('email', models.EmailField(blank=True, max_length=254, null=True)),
                 ('email_de', models.EmailField(blank=True, max_length=254, null=True)),
                 ('email_en', models.EmailField(blank=True, max_length=254, null=True)),
+                ('dynamic_default', models.CharField(default='password', max_length=255)),
+                (
+                    'dynamic_default_de',
+                    models.CharField(default='password', max_length=255, null=True),
+                ),
+                (
+                    'dynamic_default_en',
+                    models.CharField(default='password', max_length=255, null=True),
+                ),
             ],
         ),
         migrations.CreateModel(

modeltranslation/tests/models.py

@@ -11,6 +11,7 @@ class TestModel(models.Model):
     text = models.TextField(blank=True, null=True)
     url = models.URLField(blank=True, null=True)
     email = models.EmailField(blank=True, null=True)
+    dynamic_default = models.CharField(default=gettext_lazy("password"), max_length=255)
 
 
 class UniqueNullableModel(models.Model):

modeltranslation/tests/tests.py

@@ -631,6 +631,31 @@ def test_update_or_create_new(self):
             title_de='old de',
         )
 
+    def test_callable_field_default_uses_field_language(self):
+        # the test uses translations from django.contrib.auth django.po file by
+        # specifying a model default with one of the translatable literals from that
+        # app
+
+        # unsaved instance must follow django's behaviour for callable default
+        raw_instance = models.TestModel()
+
+        assert raw_instance.dynamic_default == "Passwort"
+        assert raw_instance.dynamic_default_en == "password"
+        assert raw_instance.dynamic_default_de == "Passwort"
+
+        # saved instance must have same behaviour as unsaved instance
+        instance = models.TestModel.objects.create()
+
+        assert instance.dynamic_default == "Passwort"
+        assert instance.dynamic_default_en == "password"
+        assert instance.dynamic_default_de == "Passwort"
+        assert_db_record(
+            instance,
+            dynamic_default='Passwort',
+            dynamic_default_en='password',
+            dynamic_default_de='Passwort',
+        )
+
 
 class ModeltranslationTransactionTest(ModeltranslationTransactionTestBase):
     def test_unique_nullable_field(self):
@@ -2408,6 +2433,8 @@ class TestModelAdmin(admin.TranslationAdmin):
             'url_en',
             'email_de',
             'email_en',
+            'dynamic_default_de',
+            'dynamic_default_en',
         )
 
     def test_default_fieldsets(self):
@@ -2426,6 +2453,8 @@ class TestModelAdmin(admin.TranslationAdmin):
             'url_en',
             'email_de',
             'email_en',
+            'dynamic_default_de',
+            'dynamic_default_en',
         ]
         assert ma.get_fieldsets(request) == [(None, {'fields': fields})]
         assert ma.get_fieldsets(request, self.test_obj) == [(None, {'fields': fields})]
@@ -2459,15 +2488,15 @@ class TestModelAdmin(admin.TranslationAdmin):
 
         # Using `exclude`.
         class TestModelAdmin(admin.TranslationAdmin):
-            exclude = ['url', 'email']
+            exclude = ['url', 'email', 'dynamic_default']
 
         ma = TestModelAdmin(models.TestModel, self.site)
         fields = ['title_de', 'title_en', 'text_de', 'text_en']
         assert tuple(ma.get_form(request).base_fields.keys()) == tuple(fields)
 
         # You can also pass a tuple to `exclude`.
         class TestModelAdmin(admin.TranslationAdmin):
-            exclude = ('url', 'email')
+            exclude = ('url', 'email', 'dynamic_default')
 
         ma = TestModelAdmin(models.TestModel, self.site)
         assert tuple(ma.get_form(request).base_fields.keys()) == tuple(fields)
@@ -2502,6 +2531,8 @@ class TestModelAdmin(admin.TranslationAdmin):
             'url_en',
             'email_de',
             'email_en',
+            'dynamic_default_de',
+            'dynamic_default_en',
         )
 
         # Using grouped fields.
@@ -2550,7 +2581,7 @@ class TestModelAdmin(admin.TranslationAdmin):
         class TestModelForm(forms.ModelForm):
             class Meta:
                 model = models.TestModel
-                exclude = ['url', 'email']
+                exclude = ['url', 'email', 'dynamic_default']
 
         class TestModelAdmin(admin.TranslationAdmin):
             form = TestModelForm
@@ -2564,7 +2595,7 @@ class TestModelAdmin(admin.TranslationAdmin):
         # option, the ModelAdmin wins. This is Django behaviour.
         class TestModelAdmin(admin.TranslationAdmin):
             form = TestModelForm
-            exclude = ['url']
+            exclude = ['url', 'dynamic_default']
 
         ma = TestModelAdmin(models.TestModel, self.site)
         fields = ['title_de', 'title_en', 'text_de', 'text_en', 'email_de', 'email_en']
@@ -3658,8 +3689,11 @@ class Meta:
             'email',
             'email_de',
             'email_en',
+            'dynamic_default',
+            'dynamic_default_de',
+            'dynamic_default_en',
         ]
-        assert list(form.fields) == ['title', 'text', 'url', 'email']
+        assert list(form.fields) == ['title', 'text', 'url', 'email', 'dynamic_default']
 
     def test_updating_with_empty_value(self):
         """
@@ -3670,7 +3704,7 @@ def test_updating_with_empty_value(self):
         class Form(forms.ModelForm):
             class Meta:
                 model = models.TestModel
-                exclude = ('text',)
+                exclude = ('text', 'dynamic_default')
 
         instance = models.TestModel.objects.create(text_de='something')
         form = Form(

modeltranslation/tests/translation.py

@@ -14,6 +14,7 @@ class TestTranslationOptions(TranslationOptions):
         'text',
         'url',
         'email',
+        'dynamic_default',
     )
     empty_values = ''