Bulk updating metadata from a plugin?

[kiwidude]

Hi - I'm looking at some (ancient) code in the Extract ISBN plugin.

The code just wants to update a batch of books to set the .isbn property of the Metadata. For reasons I have long since got no idea on (likely written 12+ years ago), the code appears to steal some behaviour from the Edit Metadata plugin back then. It currently looks like this:

        # At this point we want to re-use code in edit_metadata to go ahead and
        # apply the changes. So we will replace the Metadata objects with some
        # empty ones with only the isbn field set so only that field gets updated
        id_map = {}
        for i, title, last_modified, isbn in extracted_ids:
            mi = Metadata(_('Unknown'))
            mi.isbn = isbn
            id_map[i] = mi
        edit_metadata_action = self.gui.iactions['Edit Metadata']
        edit_metadata_action.apply_metadata_changes(id_map,
                                                    callback=self._mark_and_display_results)

As you can see fairly straightforward of only setting one property on the Metadata object and relying on magic inside apply_metadata_changes() to ensure only that property gets updated on the books.

It is entirely possibly that in "current" calibre this is a terrible approach and there is a better way of doing this. Thoughts/suggestions welcomed - it still seems to work perfectly fine for me but two users now are saying their titles are being reset to "unknown". I havent touched any of this code, the only change my latest plugin release made is to increase the likelihood of an ISBN being found (which would then invoke this code)...

[chaley]

I would do something like this. I didn't try to run it, but see below.

	# I assume you have an old API db reference. Get a new_api reference
	ndb = db.new_api
	book_to_id_map = {}
	for i, title, last_modified, isbn in extracted_ids:
		# Get the existing identifiers for the book
		identifiers_for_book = ndb.field_for('identifiers', i)
		# Add/replace the ISBN identifer
		identifiers_for_book['isbn'] = isbn
		# Save the (probably) updated list of identifiers
		book_to_id_map[i] = identifiers_for_book
	# Set all the books' identifier values
	ndb.set_field('identifiers', book_to_id_map)

As a test I ran this in the template tester. It worked. The first 4 books with more than one identifier ended up including "isbn:grumblebunny"

python:
def evaluate(book, context):
	db = context.db.new_api
	ids = list(db.search("identifiers:#>2"))
	book_to_id_map = {}
	for id_ in ids[0:4]:
		identifiers_for_book = db.field_for('identifiers', id_)
		identifiers_for_book['isbn'] = 'grumblebunny'
		book_to_id_map[id_] = identifiers_for_book
	db.set_field('identifiers', book_to_id_map)
	return 'foo'

[kiwidude]

Thanks very much chaley!