Use ProxyMetadata in formatter functions for virt libs, ondevice, book_size, and approximate_formats. This saves the assignment in get_metadata()

src/calibre/db/cache.py

@@ -214,8 +214,8 @@ class Cache(object):
                 default_value='dummy')
         mi.title_sort  = self._field_for('sort', book_id,
                 default_value=_('Unknown'))
-        mi.book_size   = self._field_for('size', book_id, default_value=0)
+#         mi.book_size   = self._field_for('size', book_id, default_value=0)
-        mi.ondevice_col = self._field_for('ondevice', book_id, default_value='')
+#         mi.ondevice_col = self._field_for('ondevice', book_id, default_value='')
         mi.last_modified = self._field_for('last_modified', book_id,
                 default_value=n)
         formats = self._field_for('formats', book_id)
@@ -227,7 +227,7 @@ class Cache(object):
             mi.format_metadata = FormatMetadata(self, book_id, formats)
             good_formats = FormatsList(formats, mi.format_metadata)
         mi.formats = good_formats
-        mi.db_approx_formats = formats
+#         mi.db_approx_formats = formats
         mi.has_cover = _('Yes') if self._field_for('cover', book_id,
                 default_value=False) else ''
         mi.tags = list(self._field_for('tags', book_id, default_value=()))
@@ -1413,6 +1413,7 @@ class Cache(object):
     def refresh_ondevice(self):
         self.fields['ondevice'].clear_caches()
         self.clear_search_caches()
+        self.clear_composite_caches()
 
     @read_api
     def tags_older_than(self, tag, delta=None, must_have_tag=None, must_have_authors=None):

src/calibre/db/lazy.py

@@ -355,4 +355,6 @@ class ProxyMetadata(Metadata):
         um = ga(self, '_user_metadata')
         return frozenset(ALL_METADATA_FIELDS.union(um.iterkeys()))
 
-
+    @property
+    def _proxy_metadata(self):
+        return self

src/calibre/gui2/library/models.py

@@ -453,7 +453,7 @@ class BooksModel(QAbstractTableModel):  # {{{
 
     def get_book_display_info(self, idx):
         mi = self.db.get_metadata(idx)
-        mi.size = mi.book_size
+        mi.size = mi._proxy_metadata.book_size
         mi.cover_data = ('jpg', self.cover(idx))
         mi.id = self.db.id(idx)
         mi.field_metadata = self.db.field_metadata

src/calibre/utils/formatter_functions.py

@@ -640,15 +640,22 @@ class BuiltinApproximateFormats(BuiltinFormatterFunction):
                   'although it probably is. '
                   'This function can be called in template program mode using '
                   'the template "{:\'approximate_formats()\'}". '
-                  'Note that format names are always uppercase, as in EPUB.'
+                  'Note that format names are always uppercase, as in EPUB. '
+                  'This function works only in the GUI. If you want to use these values '
+                  'in save-to-disk or send-to-device templates then you '
+                  'must make a custom "Column built from other columns", use '
+                  'the function in that column\'s template, and use that '
+                  'column\'s value in your save/send templates'
             )
 
     def evaluate(self, formatter, kwargs, mi, locals):
-        fmt_data = mi.get('db_approx_formats', [])
+        if hasattr(mi, '_proxy_metadata'):
-        if not fmt_data:
+            fmt_data = mi._proxy_metadata.db_approx_formats
-            return ''
+            if not fmt_data:
-        data = sorted(fmt_data)
+                return ''
-        return ','.join(v.upper() for v in data)
+            data = sorted(fmt_data)
+            return ','.join(v.upper() for v in data)
+        return _('This function can be used only in the GUI')
 
 class BuiltinFormatsModtimes(BuiltinFormatterFunction):
     name = 'formats_modtimes'
@@ -902,27 +909,42 @@ class BuiltinBooksize(BuiltinFormatterFunction):
     name = 'booksize'
     arg_count = 0
     category = 'Get values from metadata'
-    __doc__ = doc = _('booksize() -- return value of the size field')
+    __doc__ = doc = _('booksize() -- return value of the size field. '
+                'This function works only in the GUI. If you want to use this value '
+                'in save-to-disk or send-to-device templates then you '
+                'must make a custom "Column built from other columns", use '
+                'the function in that column\'s template, and use that '
+                'column\'s value in your save/send templates')
 
     def evaluate(self, formatter, kwargs, mi, locals):
-        if mi.book_size is not None:
+        if hasattr(mi, '_proxy_metadata'):
             try:
-                return str(mi.book_size)
+                v = mi._proxy_metadata.book_size
+                if v is not None:
+                    return str(mi._proxy_metadata.book_size)
+                return ''
             except:
                 pass
-        return ''
+            return ''
+        return _('This function can be used only in the GUI')
 
 class BuiltinOndevice(BuiltinFormatterFunction):
     name = 'ondevice'
     arg_count = 0
     category = 'Get values from metadata'
     __doc__ = doc = _('ondevice() -- return Yes if ondevice is set, otherwise return '
-            'the empty string')
+              'the empty string. This function works only in the GUI. If you want to '
+              'use this value in save-to-disk or send-to-device templates then you '
+              'must make a custom "Column built from other columns", use '
+              'the function in that column\'s template, and use that '
+              'column\'s value in your save/send templates')
 
     def evaluate(self, formatter, kwargs, mi, locals):
-        if mi.ondevice_col:
+        if hasattr(mi, '_proxy_metadata'):
-            return _('Yes')
+            if mi._proxy_metadata.ondevice_col:
-        return ''
+                return _('Yes')
+            return ''
+        return _('This function can be used only in the GUI')
 
 class BuiltinSeriesSort(BuiltinFormatterFunction):
     name = 'series_sort'
@@ -1259,9 +1281,6 @@ class BuiltinVirtualLibraries(BuiltinFormatterFunction):
                       'column\'s value in your save/send templates')
 
     def evaluate(self, formatter, kwargs, mi, locals_):
-        from calibre.db.lazy import ProxyMetadata
-        if isinstance(mi, ProxyMetadata):
-            return mi.virtual_libraries
         if hasattr(mi, '_proxy_metadata'):
             return mi._proxy_metadata.virtual_libraries
         return _('This function can be used only in the GUI')