models: restore file record key unique index

invenio_records_resources/records/models.py

@@ -57,17 +57,15 @@ def object_version(cls):
         """Object version connected to the record file."""
         return db.relationship(ObjectVersion)
 
-    # NOTE: This seems to break SQLAlchemy-Continuum versioning. We should fix it
-    #       though to make sure we don't have duplicate keys for record files.
-    # @declared_attr
-    # def __table_args__(cls):
-    #     """Table args."""
-    #     return (
-    #         # To make sure we don't have duplicate keys for record files
-    #         db.Index(
-    #             f"uidx_{cls.__tablename__}_record_id_key",
-    #             "record_id",
-    #             "key",
-    #             unique=True,
-    #         ),
-    #     )
+    @declared_attr
+    def __table_args__(cls):
+        """Table args."""
+        return (
+            # To make sure we don't have duplicate keys for record files
+            db.Index(
+                f"uidx_{cls.__tablename__}_record_id_key",
+                "record_id",
+                "key",
+                unique=True,
+            ),
+        )