feat(signals): duplicate objects with field constraints

Add pre_duplicate signal to deal with fields of entity
object instances which won't allow object duplication
(e.g. fields with unique constraints).

apis_ontology/models.py

@@ -13,7 +13,7 @@
 from django.utils.translation import gettext_lazy as _
 from multiselectfield import MultiSelectField
 
-from .signals import update_duplicates  # noqa
+from .signals import prepare_for_duplication, update_duplicates  # noqa
 
 
 logger = logging.getLogger(__name__)

apis_ontology/signals.py

@@ -1,13 +1,35 @@
 import logging
 
 from apis_core.apis_metainfo.models import RootObject
-from apis_core.apis_metainfo.signals import post_duplicate
+from apis_core.apis_metainfo.signals import post_duplicate, pre_duplicate
 from django.dispatch import receiver
 
 
 logger = logging.getLogger(__name__)
 
 
+@receiver(pre_duplicate)
+def prepare_for_duplication(sender, instance, **kwargs):
+    """
+    Prepare instances of entity classes before duplicating them
+    by removing or updating fields which won't pass validation.
+    Helps to e.g. circumvent IntegrityErrors caused by unique constraints.
+
+    :param sender: the model class
+    :param instance: the original object
+    """
+    if isinstance(instance, RootObject):
+        available_fields = [f.name for f in instance._meta.fields]
+
+        update_fields = {
+            "siglum": None,
+        }
+
+        for f, v in update_fields.items():
+            if f in available_fields:
+                setattr(instance, f, v)
+
+
 @receiver(post_duplicate)
 def update_duplicates(sender, instance, duplicate, **kwargs):
     """