newdb: Automatically fix broken link tables

Fixes #1218783 [Beim Starten von Calibre bleibt das Startlogo bestehen und Pythons meldet einen Fehler.](https://bugs.launchpad.net/calibre/+bug/1218783)

src/calibre/db/cache.py

@@ -20,7 +20,7 @@ from calibre.db import SPOOL_SIZE, _get_next_series_num_for_list
 from calibre.db.categories import get_categories
 from calibre.db.locking import create_locks
 from calibre.db.errors import NoSuchFormat
-from calibre.db.fields import create_field, IDENTITY
+from calibre.db.fields import create_field, IDENTITY, InvalidLinkTable
 from calibre.db.search import Search
 from calibre.db.tables import VirtualTable
 from calibre.db.write import get_series_values, uniq
@@ -866,10 +866,18 @@ class Cache(object):
     def search(self, query, restriction='', virtual_fields=None, book_ids=None):
         return self._search_api(self, query, restriction, virtual_fields=virtual_fields, book_ids=book_ids)
 
-    @read_api
-    def get_categories(self, sort='name', book_ids=None, icon_map=None):
-        return get_categories(self, sort=sort, book_ids=book_ids,
-                              icon_map=icon_map)
+    @api
+    def get_categories(self, sort='name', book_ids=None, icon_map=None, already_fixed=None):
+        try:
+            with self.read_lock:
+                return get_categories(self, sort=sort, book_ids=book_ids, icon_map=icon_map)
+        except InvalidLinkTable as err:
+            bad_field = err.field_name
+            if bad_field == already_fixed:
+                raise
+            with self.write_lock:
+                self.fields[bad_field].table.fix_link_table(self.backend)
+            return self.get_categories(sort=sort, book_ids=book_ids, icon_map=icon_map, already_fixed=bad_field)
 
     @write_api
     def update_last_modified(self, book_ids, now=None):

src/calibre/db/fields.py

@@ -27,6 +27,12 @@ def bool_sort_key(bools_are_tristate):
 
 IDENTITY = lambda x: x
 
+class InvalidLinkTable(Exception):
+
+    def __init__(self, name):
+        Exception.__init__(self, name)
+        self.field_name = name
+
 class Field(object):
 
     is_many = False
@@ -144,9 +150,15 @@ class Field(object):
                 ratings = tuple(r for r in (book_rating_map.get(book_id, 0) for
                                             book_id in item_book_ids) if r > 0)
                 avg = sum(ratings)/len(ratings) if ratings else 0
-                name = self.category_formatter(id_map[item_id])
+                try:
+                    name = self.category_formatter(id_map[item_id])
+                except KeyError:
+                    # db has entries in the link table without entries in the
+                    # id table, for example, see
+                    # https://bugs.launchpad.net/bugs/1218783
+                    raise InvalidLinkTable(self.name)
                 sval = (self.category_sort_value(item_id, item_book_ids, lang_map)
-                        if special_sort else name)
+                    if special_sort else name)
                 c = tag_class(name, id=item_id, sort=sval, avg=avg,
                               id_set=item_book_ids, count=len(item_book_ids))
                 ans.append(c)

src/calibre/db/tables.py

@@ -64,6 +64,9 @@ class Table(object):
     def remove_books(self, book_ids, db):
         return set()
 
+    def fix_link_table(self, db):
+        pass
+
 class VirtualTable(Table):
 
     '''
@@ -201,6 +204,17 @@ class ManyToOneTable(Table):
             cbm[item_id].add(book)
             bcm[book] = item_id
 
+    def fix_link_table(self, db):
+        linked_item_ids = {item_id for item_id in self.book_col_map.itervalues()}
+        extra_item_ids = linked_item_ids - set(self.id_map)
+        if extra_item_ids:
+            for item_id in extra_item_ids:
+                book_ids = self.col_book_map.pop(item_id, ())
+                for book_id in book_ids:
+                    self.book_col_map.pop(book_id, None)
+            db.conn.executemany('DELETE FROM {0} WHERE {1}=?'.format(
+                self.link_table, self.metadata['link_column']), tuple((x,) for x in extra_item_ids))
+
     def remove_books(self, book_ids, db):
         clean = set()
         for book_id in book_ids:
@@ -284,6 +298,17 @@ class ManyToManyTable(ManyToOneTable):
 
         self.book_col_map = {k:tuple(v) for k, v in bcm.iteritems()}
 
+    def fix_link_table(self, db):
+        linked_item_ids = {item_id for item_ids in self.book_col_map.itervalues() for item_id in item_ids}
+        extra_item_ids = linked_item_ids - set(self.id_map)
+        if extra_item_ids:
+            for item_id in extra_item_ids:
+                book_ids = self.col_book_map.pop(item_id, ())
+                for book_id in book_ids:
+                    self.book_col_map[book_id] = tuple(iid for iid in self.book_col_map.pop(book_id, ()) if iid not in extra_item_ids)
+            db.conn.executemany('DELETE FROM {0} WHERE {1}=?'.format(
+                self.link_table, self.metadata['link_column']), tuple((x,) for x in extra_item_ids))
+
     def remove_books(self, book_ids, db):
         clean = set()
         for book_id in book_ids: