From e2c3bb40a51a3f11137a047fbfe0d2d2edbb81e4 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Thu, 1 Aug 2013 07:41:49 +0530
Subject: [PATCH] newdb: Fix default value for identifiers is mutable

---
 src/calibre/db/fields.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/calibre/db/fields.py b/src/calibre/db/fields.py
index 50fa658b29..e47e366c9b 100644
--- a/src/calibre/db/fields.py
+++ b/src/calibre/db/fields.py
@@ -410,7 +410,10 @@ class IdentifiersField(ManyToManyField):
     def for_book(self, book_id, default_value=None):
         ids = self.table.book_col_map.get(book_id, ())
         if not ids:
-            ids = default_value
+            try:
+                ids = default_value.copy()  # in case default_value is a mutable dict
+            except AttributeError:
+                ids = default_value
         return ids
 
     def sort_keys_for_books(self, get_metadata, lang_map, all_book_ids):