From 31467359620cbb35e6533f0a5e8c7b0b0eb2afc6 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sat, 21 Feb 2015 14:07:49 +0530
Subject: [PATCH] Fix regression in 2.20 that prevented some plugins from
 updating their preferences

---
 src/calibre/db/backend.py       | 14 ++++++--------
 src/calibre/db/tests/writing.py | 16 ++++++++++++++++
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/src/calibre/db/backend.py b/src/calibre/db/backend.py
index abe07a12a1..5077d1f1a7 100644
--- a/src/calibre/db/backend.py
+++ b/src/calibre/db/backend.py
@@ -107,14 +107,12 @@ class DBPrefs(dict):  # {{{
 
     def __setitem__(self, key, val):
         if not self.disable_setting:
-            try:
-                current_val = self[key]
-            except KeyError:
-                current_val = object()
-            if val != current_val:
-                raw = self.to_raw(val)
-                self.db.execute('INSERT OR REPLACE INTO preferences (key,val) VALUES (?,?)', (key, raw))
-                dict.__setitem__(self, key, val)
+            raw = self.to_raw(val)
+            with self.db.conn:
+                dbraw = self.db.execute('SELECT val FROM preferences WHERE key=?', (key,)).fetchone()
+                if dbraw != raw:
+                    self.db.execute('INSERT OR REPLACE INTO preferences (key,val) VALUES (?,?)', (key, raw))
+                    dict.__setitem__(self, key, val)
 
     def set(self, key, val):
         self.__setitem__(key, val)
diff --git a/src/calibre/db/tests/writing.py b/src/calibre/db/tests/writing.py
index 175043ce6a..eca53bd86b 100644
--- a/src/calibre/db/tests/writing.py
+++ b/src/calibre/db/tests/writing.py
@@ -7,6 +7,7 @@ __license__   = 'GPL v3'
 __copyright__ = '2013, Kovid Goyal <kovid at kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
+import os
 from collections import namedtuple
 from functools import partial
 from io import BytesIO
@@ -692,3 +693,18 @@ class WritingTest(BaseTest):
             ae(c.field_for('tags', 3), (t.id_map[lid], t.id_map[norm]))
     # }}}
 
+    def test_preferences(self):  # {{{
+        ' Test getting and setting of preferences, especially with mutable objects '
+        cache = self.init_cache()
+        prefs = cache.backend.prefs
+        prefs['test mutable'] =  [1, 2, 3]
+        a = prefs['test mutable']
+        a.append(4)
+        self.assertIn(4, prefs['test mutable'])
+        prefs['test mutable'] = a
+        prefs.load_from_db()
+        self.assertIn(4, prefs['test mutable'])
+        before = os.stat(cache.backend.library_path)
+        prefs['test mutable'] = a
+        self.assertEqual(before, os.stat(cache.backend.library_path), 'The database was written to despite there being no change in value')
+    # }}}