diff --git a/src/calibre/library/database2.py b/src/calibre/library/database2.py
index a23e243a23..513f0bc690 100644
--- a/src/calibre/library/database2.py
+++ b/src/calibre/library/database2.py
@@ -7,8 +7,8 @@ __docformat__ = 'restructuredtext en'
 The database used to store ebook metadata
 '''
 import os, sys, shutil, cStringIO, glob, time, functools, traceback, re, \
-        json, uuid, hashlib, copy
-from collections import defaultdict
+        json, uuid, hashlib, copy, weakref
+from collections import defaultdict, MutableMapping, MutableSequence
 import threading, random
 from itertools import repeat
 from math import ceil
@@ -81,6 +81,109 @@ class Tag(object):
     def __repr__(self):
         return str(self)
 
+class MutablePrintMixin(object): # {{{
+    def __str__(self):
+        self._resolve()
+        return str(self.values)
+
+    def __repr__(self):
+        self._resolve()
+        return repr(self.values)
+
+    def __unicode__(self):
+        self._resolve()
+        return unicode(self.values)
+# }}}
+
+class FormatMetadata(MutableMapping, MutablePrintMixin): # {{{
+
+    def __init__(self, db, id_, formats):
+        self.dbwref = weakref.ref(db)
+        self.id_ = id_
+        self.formats = formats
+        self._must_do = True
+        self.values = {}
+
+    def _resolve(self):
+        if self._must_do:
+            self._must_do = False
+            db = self.dbwref()
+            for f in self.formats:
+                try:
+                    self.values[f] = db.format_metadata(self.id_, f)
+                except:
+                    pass
+
+    def __contains__(self, key):
+        self._resolve()
+        return key in self.values
+
+    def __getitem__(self, fmt):
+        self._resolve()
+        return self.values[fmt]
+
+    def __setitem__(self, key, val):
+        self._resolve()
+        self.values[key] = val
+
+    def __delitem__(self, key):
+        self._resolve()
+        self.values.__delitem__(key)
+
+    def __len__(self):
+        self._resolve()
+        return len(self.values)
+
+    def __iter__(self):
+        self._resolve()
+        return self.values.__iter__()
+
+
+class FormatsList(MutableSequence, MutablePrintMixin):
+
+    def __init__(self, formats, format_metadata):
+        self.formats = formats
+        self.format_metadata = format_metadata
+        self._must_do = True
+        self.values = []
+
+    def _resolve(self):
+        if self._must_do:
+            self._must_do = False
+            for f in self.formats:
+                try:
+                    if f in self.format_metadata:
+                        self.values.append(f)
+                except:
+                    pass
+
+    def __getitem__(self, dex):
+        self._resolve()
+        return self.values[dex]
+
+    def __setitem__(self, key, dex):
+        self._resolve()
+        self.values[key] = dex
+
+    def __delitem__(self, dex):
+        self._resolve()
+        self.values.__delitem__(dex)
+
+    def __len__(self):
+        self._resolve()
+        return len(self.values)
+
+    def __iter__(self):
+        self._resolve()
+        return self.values.__iter__()
+
+    def insert(self, idx, val):
+        self._resolve()
+        self.values.insert(idx, val)
+
+# }}}
+
+
 
 class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
     '''
@@ -944,14 +1047,8 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
             good_formats = None
         else:
             formats = sorted(formats.split(','))
-            good_formats = []
-            for f in formats:
-                try:
-                    mi.format_metadata[f] = self.format_metadata(id, f)
-                except:
-                    pass
-                else:
-                    good_formats.append(f)
+            mi.format_metadata = FormatMetadata(self, id, formats)
+            good_formats = FormatsList(formats, mi.format_metadata)
         mi.formats = good_formats
         tags = row[fm['tags']]
         if tags: