tomleo · January 30, 2020 17:58 · Jan 30, 2020
diff --git a/db_constraint_example.py b/db_constraint_example.py
@@ -0,0 +1,40 @@
+class Foo(models.Model):
+
+
+    def object_validation(
+        cls, some_values
+    ) -> Optional[str]:
+        """
+        Validation logic when creating a Foo record
+
+        If creation is via a model serializer's is_valid method this function
+        will get triggered via the clean method.
+
+        If creation is not via a model serializer's is_valid method this
+        function will get triggered via the save method.
+        """
+        if not some_value == "somethong":
+            return FOO_ERROR_MSG_SOMETHING_GOES_HERE
+        return None
+
+    def clean(self):
+        """
+        `is_valid` calls on model serializers should trigger this validation prior to saving
+        """
+        error_msg = self.content_object_validation(
+            some_value
+        )
+        if error_msg:
+            raise ValidationError(error_msg)
+
+    def save(self, *args, **kwargs):
+        """
+        Ensure new objects are valid prior to save.
+        """
+        if not self.id:
+            error_msg = self.content_object_validation(
+                some_value
+            )
+            if error_msg:
+                raise IntegrityError(error_msg)
+        super().save(*args, **kwargs)