[books] Really fix the subtitle bug

vrobbler/apps/books/models.py

@@ -71,7 +71,7 @@ class BookLogData(BaseLogData, LongPlayLogData):
     _excluded_fields = {"koreader_hash", "page_data"}
 
     def avg_seconds_per_page(self):
-        if self.page_data:
+        if self.page_data and isinstance(self.page_data, dict):
             total_duration = 0
             for page_num, stats in self.page_data.items():
                 total_duration += stats.get("duration", 0)
@@ -173,6 +173,9 @@ class Book(LongPlayScrobblableMixin):
     genre = TaggableManager(through=ObjectWithGenres, blank=True, verbose_name="Genre")
 
     def __str__(self) -> str:
+        if not self.subtitle:
+            return self.title
+
         return f"{self.title} - {self.subtitle}"
 
     def save(self, *args, **kwargs):
@@ -184,14 +187,18 @@ class Book(LongPlayScrobblableMixin):
 
     @property
     def subtitle(self):
-        subtitle = ""
+        subtitle_parts = []
         if self.author:
-            subtitle += self.author.name
+            subtitle_parts.append(self.author.name)
         if self.issue_number and "Issue" not in str(self.title):
-            subtitle += " - Issue {self.issue_number}"
+            subtitle_parts.append(f"Issue {self.issue_number}")
         if self.volume_number and "Volume" not in str(self.title):
-            subtitle += " - Volume {self.volume_number}"
-        return subtitle
+            subtitle_parts.append(f"Volume {self.volume_number}")
+        if len(subtitle_parts) > 1:
+            return " / ".join(subtitle_parts)
+        if len(subtitle_parts) == 1:
+            return subtitle_parts[0]
+        return ""
 
     @property
     def strings(self) -> ScrobblableConstants: