fix: Fix patching unique_together for migrations

Refs #785

Author: last-partizan

modeltranslation/tests/migrations/0001_initial.py

@@ -1,4 +1,4 @@
-# Generated by Django 5.2.4 on 2025-09-14 04:17
+# Generated by Django 5.2.4 on 2025-09-14 05:04
 
 import django.contrib.auth.models
 import django.core.validators
@@ -943,6 +943,11 @@ class Migration(migrations.Migration):
                         name="unique_fields-sub_title_en",
                     ),
                 ],
+                "unique_together": {
+                    ("title", "sub_title"),
+                    ("title", "sub_title_de"),
+                    ("title", "sub_title_en"),
+                },
             },
         ),
         migrations.CreateModel(

modeltranslation/tests/models.py

@@ -27,6 +27,7 @@ class ModelWithConstraint(models.Model):
     sub_title = models.CharField(max_length=255)
 
     class Meta:
+        unique_together = (("title", "sub_title"),)
         constraints = [
             models.UniqueConstraint(
                 fields=["title", "sub_title"],

modeltranslation/translator.py

@@ -357,6 +357,10 @@ def add_constraints():
 
     model._meta.unique_together += tuple(add_unique_together())  # type: ignore[operator]
     model._meta.constraints += tuple(add_constraints())
+    # `unique_together` needs `original_attrs` to be set, for this changes to appear in migrations.
+    for attr_name in ("unique_together",):
+        if value := getattr(model._meta, attr_name):
+            model._meta.original_attrs[attr_name] = value
 
 
 def delete_mt_init(sender: type[Model], instance: Model, **kwargs: Any) -> None: