From 937a362ba8599c9571824493c13fed05223fb561 Mon Sep 17 00:00:00 2001
From: Radek Czajka <rczajka@rczajka.pl>
Date: Thu, 10 Nov 2022 11:08:58 +0100
Subject: [PATCH 1/1] Fix errors on serializing unsaved wikidata imports.

---
 src/catalogue/models.py | 4 ++++
 src/catalogue/views.py  | 6 +++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/catalogue/models.py b/src/catalogue/models.py
index 92b27651..f9a2ecfe 100644
--- a/src/catalogue/models.py
+++ b/src/catalogue/models.py
@@ -227,11 +227,15 @@ class Book(WikidataModel):
         return f'https://wolnelektury.pl/katalog/lektura/{self.slug}/'
     
     def authors_str(self):
+        if not self.pk:
+            return ''
         return ", ".join(str(author) for author in self.authors.all())
     authors_str.admin_order_field = 'authors__last_name'
     authors_str.short_description = _('Author')
 
     def translators_str(self):
+        if not self.pk:
+            return ''
         return ", ".join(str(author) for author in self.translators.all())
     translators_str.admin_order_field = 'translators__last_name'
     translators_str.short_description = _('Translator')
diff --git a/src/catalogue/views.py b/src/catalogue/views.py
index 889a8321..3e55d693 100644
--- a/src/catalogue/views.py
+++ b/src/catalogue/views.py
@@ -165,7 +165,11 @@ class WikidataView(APIView):
             if attname.startswith("_"):
                 continue
             for fieldname, lang in obj.wikidata_fields_for_attribute(attname):
-                d[fieldname] = getattr(obj, fieldname)
+                try:
+                    d[fieldname] = getattr(obj, fieldname)
+                except ValueError:
+                    # Like accessing related field on non-saved object.
+                    continue
 
                 if isinstance(d[fieldname], models.WikidataModel):
                     d[fieldname] = {
-- 
2.20.1