Fix issue #261: Handle unique constraint validation error

modeltranslation/admin.py

@@ -238,9 +238,27 @@ def _get_form_or_formset(
             exclude.extend(self.form._meta.exclude)
         # If exclude is an empty list we pass None to be consistent with the
         # default on modelform_factory
-        exclude = self.replace_orig_field(exclude) or None
-        exclude = self._exclude_original_fields(exclude)
-        kwargs.update({"exclude": exclude})
+        updated_exclude = self.replace_orig_field(exclude) or None
+        # Copy default language field value into the original field.
+        if request.POST:
+            data = request.POST.copy()
+            for field in self.trans_opts.fields:
+                default_lang_field = build_localized_fieldname(field, mt_settings.DEFAULT_LANGUAGE)
+                if default_lang_field in data:
+                    value = data.get(default_lang_field)
+                    if field not in data.keys() and value:
+                        data.appendlist(field, value)
+            request.POST = data  # type: ignore[assignment]
+        # In order for BaseModelAdmin to show unique-constraint validation error,
+        # add the original translation fields to kwargs, and do not exclude the
+        # original translation fields.
+        if kwargs.get("fields"):
+            original_fields = [field for field in self.trans_opts.fields if field not in exclude]
+            kwargs["fields"].extend(original_fields)
+            kwargs.update({"exclude": (updated_exclude and list({*exclude, *updated_exclude}))})
+        else:
+            updated_exclude = self._exclude_original_fields(updated_exclude)
+            kwargs.update({"exclude": updated_exclude})
 
         return kwargs
 

modeltranslation/tests/test_admin_views.py

@@ -1,17 +1,25 @@
+"""Tests for admin view."""
+
 from django.test import Client
 from django.urls import reverse
-import pytest
+
 from modeltranslation.tests.models import ModelWithConstraint
-from django.db import IntegrityError
 
 
 def test_create_duplicate(admin_client: Client):
+    """Unique constraint error should be handled by TranslationAdmin."""
     ModelWithConstraint.objects.create(title="1", sub_title="One")
     url = reverse("admin:tests_modelwithconstraint_add")
 
-    with pytest.raises(IntegrityError):
-        response = admin_client.post(
-            url, {"title": "1", "sub_title_en": "One", "sub_title_de": "Ein"}
-        )
+    response = admin_client.post(
+        url,
+        {
+            "title": "1",
+            "sub_title_en": "One",
+            "sub_title_de": "Ein",
+        },
+    )
 
-        assert response.status_code == 302
+    error_msg = "Model with constraint with this Title and Sub title already exists."
+    assert error_msg in response.context["errors"][0]
+    assert response.status_code == 200