Clean up DB code from previous PR

Note that string literals in SQLITE should be single quoted.
https://sqlite.org/quirks.html#dblquote

resources/metadata_sqlite.sql

@@ -97,6 +97,7 @@ CREATE TABLE identifiers  ( id     INTEGER PRIMARY KEY,
         );
 CREATE TABLE languages    ( id        INTEGER PRIMARY KEY,
                                     lang_code TEXT NOT NULL COLLATE NOCASE,
+							        link TEXT NOT NULL DEFAULT '',
                                     UNIQUE(lang_code)
         );
 CREATE TABLE library_id ( id   INTEGER PRIMARY KEY,
@@ -116,19 +117,23 @@ CREATE TABLE preferences(id INTEGER PRIMARY KEY,
 CREATE TABLE publishers ( id   INTEGER PRIMARY KEY,
                                   name TEXT NOT NULL COLLATE NOCASE,
                                   sort TEXT COLLATE NOCASE,
+								  link TEXT NOT NULL DEFAULT '',
                                   UNIQUE(name)
                              );
 CREATE TABLE ratings ( id   INTEGER PRIMARY KEY,
                                rating INTEGER CHECK(rating > -1 AND rating < 11),
+							   link TEXT NOT NULL DEFAULT '',
                                UNIQUE (rating)
                              );
 CREATE TABLE series ( id   INTEGER PRIMARY KEY,
                               name TEXT NOT NULL COLLATE NOCASE,
                               sort TEXT COLLATE NOCASE,
+							  link TEXT NOT NULL DEFAULT '',
                               UNIQUE (name)
                              );
 CREATE TABLE tags ( id   INTEGER PRIMARY KEY,
                             name TEXT NOT NULL COLLATE NOCASE,
+							link TEXT NOT NULL DEFAULT '',
                             UNIQUE (name)
                              );
 CREATE TABLE last_read_positions ( id INTEGER PRIMARY KEY,
@@ -633,4 +638,4 @@ CREATE TRIGGER series_update_trg
         BEGIN
           UPDATE series SET sort=title_sort(NEW.name) WHERE id=NEW.id;
         END;
-pragma user_version=25;
+pragma user_version=26;

src/calibre/db/cache.py

@@ -2341,10 +2341,7 @@ class Cache:
 
     @read_api
     def has_link_map(self, field):
-        if field not in self.fields:
+        return hasattr(getattr(self.fields.get(field), 'table', None), 'link_map')
-            raise ValueError(f'Lookup name {field} is not a valid name')
-        table = self.fields[field].table
-        return hasattr(table, 'link_map')
 
     @read_api
     def get_link_map(self, for_field):
@@ -2358,11 +2355,12 @@ class Cache:
         if for_field not in self.fields:
             raise ValueError(f'Lookup name {for_field} is not a valid name')
         table = self.fields[for_field].table
-        if not hasattr(table, 'link_map'):
+        lm = getattr(table, 'link_map', None)
+        if lm is None:
             raise ValueError(f"Lookup name {for_field} doesn't have a link map")
         lm = table.link_map
         vm = table.id_map
-        return dict({vm.get(fid, None):v for fid,v in lm.items() if v})
+        return {vm.get(fid):v for fid,v in lm.items() if v}
 
     @read_api
     def get_all_link_maps_for_book(self, book_id):
@@ -2381,21 +2379,22 @@ class Cache:
                  If book 2's author is neither A nor B and has no tags, this
                  method returns {}
         '''
-        if book_id in self.link_maps_cache:
+        cached = self.link_maps_cache.get(book_id)
-            return self.link_maps_cache[book_id]
+        if cached is not None:
+            return cached
         links = {}
         def add_links_for_field(f):
             field_ids = frozenset(self.field_ids_for(f, book_id))
             table = self.fields[f].table
             lm = table.link_map
             vm = table.id_map
-            d = dict({vm.get(fid, None):v for fid,v in lm.items() if v and fid in field_ids})
+            d = {vm.get(fid):v for fid,v in lm.items() if v and fid in field_ids}
             if d:
                 links[f] = d
         for field in ('authors', 'publisher', 'series', 'tags'):
             add_links_for_field(field)
         for field in self.field_metadata.custom_field_keys(include_composites=False):
-            if self.has_link_map(field):
+            if self._has_link_map(field):
                 add_links_for_field(field)
         self.link_maps_cache[book_id] = links
         return links
@@ -2415,8 +2414,8 @@ class Cache:
         '''
         if field not in self.fields:
             raise ValueError(f'Lookup name {field} is not a valid name')
-        table = self.fields[field].table
+        table = getattr(self.fields[field], 'table', None)
-        if not hasattr(table, 'link_map'):
+        if table is None:
             raise ValueError(f"Lookup name {field} doesn't have a link map")
         # Clear the links for book cache as we don't know what will be affected
         self.link_maps_cache = {}

src/calibre/db/schema_upgrades.py

@@ -810,14 +810,13 @@ CREATE TRIGGER fkc_annot_update
                     }
             if data['normalized']:
                 tn = 'custom_column_{}'.format(data['num'])
-                alters.append(f'ALTER TABLE {tn} ADD COLUMN link TEXT NOT NULL DEFAULT "";')
+                alters.append(f"ALTER TABLE {tn} ADD COLUMN link TEXT NOT NULL DEFAULT '';")
 
-        alters.append('ALTER TABLE publishers ADD COLUMN link TEXT NOT NULL DEFAULT "";')
+        alters.append("ALTER TABLE publishers ADD COLUMN link TEXT NOT NULL DEFAULT '';")
-        alters.append('ALTER TABLE series ADD COLUMN link TEXT NOT NULL DEFAULT "";')
+        alters.append("ALTER TABLE series ADD COLUMN link TEXT NOT NULL DEFAULT '';")
-        alters.append('ALTER TABLE tags ADD COLUMN link TEXT NOT NULL DEFAULT "";')
+        alters.append("ALTER TABLE tags ADD COLUMN link TEXT NOT NULL DEFAULT '';")
         # These aren't necessary in that there is no UI to set links, but having them
         # makes the code uniform
-        alters.append('ALTER TABLE languages ADD COLUMN link TEXT NOT NULL DEFAULT "";')
+        alters.append("ALTER TABLE languages ADD COLUMN link TEXT NOT NULL DEFAULT '';")
-        alters.append('ALTER TABLE ratings ADD COLUMN link TEXT NOT NULL DEFAULT "";')
+        alters.append("ALTER TABLE ratings ADD COLUMN link TEXT NOT NULL DEFAULT '';")
         self.db.execute('\n'.join(alters))
-

src/calibre/db/tables.py

@@ -16,6 +16,9 @@ from calibre_extensions.speedup import parse_date as _c_speedup
 from polyglot.builtins import iteritems, itervalues
 
 
+def identity(x):
+    return x
+
 def c_parse(val):
     try:
         year, month, day, hour, minutes, seconds, tzsecs = _c_speedup(val)
@@ -208,10 +211,7 @@ class ManyToOneTable(Table):
     def read_id_maps(self, db):
         query = db.execute('SELECT id, {}, link FROM {}'.format(
             self.metadata['column'], self.metadata['table']))
-        if self.unserialize is None:
+        us = identity if self.unserialize is None else self.unserialize
-            us = lambda x: x
-        else:
-            us = self.unserialize
         for id_, val, link in query:
             self.id_map[id_] = us(val)
             self.link_map[id_] = link
@@ -347,11 +347,12 @@ class ManyToOneTable(Table):
         return affected_books, new_id
 
     def set_links(self, link_map, db):
-        link_map = {id_:(l or '').strip() for id_, l in iteritems(link_map)}
+        link_map = {id_:(l or '').strip() for id_, l in link_map.items()}
-        link_map = {id_:l for id_, l in iteritems(link_map) if l != self.link_map.get(id_)}
+        link_map = {id_:l for id_, l in link_map.items() if l != self.link_map.get(id_)}
-        self.link_map.update(link_map)
+        if link_map:
-        db.executemany(f'UPDATE {self.metadata["table"]} SET link=? WHERE id=?',
+            self.link_map.update(link_map)
-            [(v, k) for k, v in iteritems(link_map)])
+            db.executemany(f'UPDATE {self.metadata["table"]} SET link=? WHERE id=?',
+                tuple((v, k) for k, v in link_map.items()))
         return link_map