further refactor into mixins

ormar/models/mixins/save_mixin.py

@@ -0,0 +1,47 @@
+from typing import Dict
+
+import ormar
+from ormar.exceptions import ModelPersistenceError
+from ormar.models.mixins.relation_mixin import RelationMixin
+
+
+class SavePrepareMixin(RelationMixin):
+    @classmethod
+    def substitute_models_with_pks(cls, model_dict: Dict) -> Dict:  # noqa  CCR001
+        for field in cls.extract_related_names():
+            field_value = model_dict.get(field, None)
+            if field_value is not None:
+                target_field = cls.Meta.model_fields[field]
+                target_pkname = target_field.to.Meta.pkname
+                if isinstance(field_value, ormar.Model):
+                    pk_value = getattr(field_value, target_pkname)
+                    if not pk_value:
+                        raise ModelPersistenceError(
+                            f"You cannot save {field_value.get_name()} "
+                            f"model without pk set!"
+                        )
+                    model_dict[field] = pk_value
+                elif field_value:  # nested dict
+                    if isinstance(field_value, list):
+                        model_dict[field] = [
+                            target.get(target_pkname) for target in field_value
+                        ]
+                    else:
+                        model_dict[field] = field_value.get(target_pkname)
+                else:
+                    model_dict.pop(field, None)
+        return model_dict
+
+    @classmethod
+    def populate_default_values(cls, new_kwargs: Dict) -> Dict:
+        for field_name, field in cls.Meta.model_fields.items():
+            if (
+                field_name not in new_kwargs
+                and field.has_default(use_server=False)
+                and not field.pydantic_only
+            ):
+                new_kwargs[field_name] = field.get_default()
+            # clear fields with server_default set as None
+            if field.server_default is not None and not new_kwargs.get(field_name):
+                new_kwargs.pop(field_name, None)
+        return new_kwargs