Пример #1
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    def create_missing_books(self, subset=None):
        """Finds books present in the PG catalog but missing from Edition.

        Yields (Edition, LicensePool) 2-tuples.
        """
        books = list(self.all_books())
        for pg_id, archive, archive_item in books:
            if subset is not None and not subset(pg_id, archive, archive_item):
                continue
            self.log.info("Considering %s" % pg_id)
            # Find an existing Edition for the book.
            book = Edition.for_foreign_id(
                self._db, self.source, Identifier.GUTENBERG_ID, pg_id,
                create_if_not_exists=False)

            if not book:
                # Create a new Edition object with bibliographic
                # information from the Project Gutenberg RDF file.
                fh = archive.extractfile(archive_item)
                data = fh.read()
                fake_fh = StringIO(data)
                book, license, new = GutenbergRDFExtractor.book_in(
                    self.collection, pg_id, fake_fh)

                if book and license:
                    yield (book, license)
Пример #2
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    def update_licensepool_with_book_info(self, book, license_pool, is_new_pool):
        """Update a book's LicensePool with information from a JSON
        representation of its circulation info.

        Then, create an Edition and make sure it has bibliographic
        coverage. If the new Edition is the only candidate for the
        pool's presentation_edition, promote it to presentation
        status.
        """
        circulation = OverdriveRepresentationExtractor.book_info_to_circulation(
            book
        )
        license_pool, circulation_changed = circulation.apply(license_pool)

        edition, is_new_edition = Edition.for_foreign_id(
            self._db, self.source, license_pool.identifier.type,
            license_pool.identifier.identifier)

        # If the pool does not already have a presentation edition, 
        # and if this edition is newly made, then associate pool and edition
        # as presentation_edition
        if ((not license_pool.presentation_edition) and is_new_edition): 
            edition_changed = license_pool.set_presentation_edition(
                policy=None
            )

        if is_new_pool:
            license_pool.open_access = False
            self.log.info("New Overdrive book discovered: %r", edition)
        return license_pool, is_new_pool, circulation_changed
Пример #3
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    def update_licensepool_with_book_info(self, book, license_pool,
                                          is_new_pool):
        """Update a book's LicensePool with information from a JSON
        representation of its circulation info.

        Then, create an Edition and make sure it has bibliographic
        coverage. If the new Edition is the only candidate for the
        pool's presentation_edition, promote it to presentation
        status.
        """
        circulation = OverdriveRepresentationExtractor.book_info_to_circulation(
            book)
        license_pool, circulation_changed = circulation.apply(
            self._db, license_pool.collection)

        edition, is_new_edition = Edition.for_foreign_id(
            self._db, self.source, license_pool.identifier.type,
            license_pool.identifier.identifier)

        # If the pool does not already have a presentation edition,
        # and if this edition is newly made, then associate pool and edition
        # as presentation_edition
        if ((not license_pool.presentation_edition) and is_new_edition):
            edition_changed = license_pool.set_presentation_edition()

        if is_new_pool:
            license_pool.open_access = False
            self.log.info("New Overdrive book discovered: %r", edition)
        return license_pool, is_new_pool, circulation_changed
    def process_item(self, identifier):
        """Associate bibliographic metadata with the given Identifier.

        :param Identifier: Look up this Identifier on Content Cafe.
        """
        try:
            # Create a Metadata object.
            metadata = self.content_cafe.create_metadata(identifier)
            if not metadata:
                # TODO: The only time this is really a transient error
                # is when the book is too new for Content Cafe to know
                # about it, which isn't often. It would be best to
                # keep this as a transient failure but give it a relatively
                # long and exponentially increasing retry time.
                return self.failure(
                    identifier,
                    "Content Cafe has no knowledge of this identifier.",
                    transient=True
                )
            edition, is_new = Edition.for_foreign_id(
                self._db, self.data_source, identifier.type,
                identifier.identifier
            )
            # We're passing in collection=None even though we
            # technically have a Collection available, because our
            # goal is to add metadata for the book without reference
            # to any particular collection.
            metadata.apply(
                edition, collection=None, replace=self.replacement_policy
            )
            return identifier
        except Exception as e:
            self.log.error('Coverage error for %r', identifier, exc_info=e)
            return self.failure(identifier, repr(e), transient=True)
Пример #5
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    def process_item(self, identifier):
        """Associate bibliographic metadata with the given Identifier.

        :param Identifier: Look up this Identifier on Content Cafe.
        """
        try:
            # Create a Metadata object.
            metadata = self.content_cafe.create_metadata(identifier)
            if not metadata:
                # TODO: The only time this is really a transient error
                # is when the book is too new for Content Cafe to know
                # about it, which isn't often. It would be best to
                # keep this as a transient failure but give it a relatively
                # long and exponentially increasing retry time.
                return self.failure(
                    identifier,
                    "Content Cafe has no knowledge of this identifier.",
                    transient=True)
            edition, is_new = Edition.for_foreign_id(self._db,
                                                     self.data_source,
                                                     identifier.type,
                                                     identifier.identifier)
            # We're passing in collection=None even though we
            # technically have a Collection available, because our
            # goal is to add metadata for the book without reference
            # to any particular collection.
            metadata.apply(edition,
                           collection=None,
                           replace=self.replacement_policy)
            return identifier
        except Exception as e:
            self.log.error('Coverage error for %r', identifier, exc_info=e)
            return self.failure(identifier, repr(e), transient=True)
Пример #6
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    def test_finalize_edition(self):

        provider_no_presentation_ready = self._provider(presentation_ready_on_success=False)
        provider_presentation_ready = self._provider(presentation_ready_on_success=True)
        identifier = self._identifier()
        source = DataSource.lookup(self._db, DataSource.GUTENBERG)

        # Here's an Edition with no LicensePool.
        edition, is_new = Edition.for_foreign_id(
            self._db, source, identifier.type, identifier.identifier
        )
        edition.title = self._str

        # This will effectively do nothing.
        provider_no_presentation_ready.finalize_edition(edition)

        # No Works have been created.
        eq_(0, self._db.query(Work).count())

        # But if there's also a LicensePool...
        pool, is_new = LicensePool.for_foreign_id(
            self._db, source, identifier.type, identifier.identifier
        )

        # finalize_edition() will create a Work.
        provider_no_presentation_ready.finalize_edition(edition)

        work = pool.work
        eq_(work, edition.work)
        eq_(False, work.presentation_ready)

        # If the provider is configured to do so, finalize_edition()
        # will also set the Work as presentation-ready.
        provider_presentation_ready.finalize_edition(edition)
        eq_(True, work.presentation_ready)
Пример #7
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 def _edition(self, licensepool):
     """Find or create the Edition that would be used to contain
     Overdrive metadata for the given LicensePool.
     """
     return Edition.for_foreign_id(
         self._db, self.source, licensepool.identifier.type,
         licensepool.identifier.identifier
     )
Пример #8
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 def _edition(self, licensepool):
     """Find or create the Edition that would be used to contain
     Overdrive metadata for the given LicensePool.
     """
     return Edition.for_foreign_id(
         self._db, self.source, licensepool.identifier.type,
         licensepool.identifier.identifier
     )
Пример #9
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 def edition(self, identifier):
     """Finds or creates an edition with license-offering DataSource.GUTENBERG
     instead of the class's local DataSource.GUTENBERG_EPUB_GENERATOR
     """
     edition, is_new = Edition.for_foreign_id(
         self._db, DataSource.GUTENBERG,
         identifier.type, identifier.identifier
     )
     return edition
Пример #10
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 def items_that_need_coverage(self):
     """Returns Editions associated with an open-access LicensePool but
     with no open-access download URL.
     """
     q = Edition.missing_coverage_from(self._db, [], self.coverage_source)
     clause = and_(Edition.data_source_id==LicensePool.data_source_id,
                   Edition.primary_identifier_id==LicensePool.identifier_id)
     q = q.join(LicensePool, clause)
     q = q.filter(LicensePool.open_access == True).filter(
         Edition.open_access_download_url==None
     )
     return q
Пример #11
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    def handle_event(self, bibliotheca_id, isbn, foreign_patron_id, start_time,
                     end_time, internal_event_type):
        # Find or lookup the LicensePool for this event.
        license_pool, is_new = LicensePool.for_foreign_id(
            self._db,
            self.api.source,
            Identifier.BIBLIOTHECA_ID,
            bibliotheca_id,
            collection=self.collection)

        if is_new:
            # This is a new book. Immediately acquire bibliographic
            # coverage for it.  This will set the
            # DistributionMechanisms and make the book
            # presentation-ready. However, its circulation information
            # might not be up to date until we process some more
            # events.
            record = self.bibliographic_coverage_provider.ensure_coverage(
                license_pool.identifier, force=True)

        bibliotheca_identifier = license_pool.identifier
        isbn, ignore = Identifier.for_foreign_id(self._db, Identifier.ISBN,
                                                 isbn)

        edition, ignore = Edition.for_foreign_id(self._db, self.api.source,
                                                 Identifier.BIBLIOTHECA_ID,
                                                 bibliotheca_id)

        # The ISBN and the Bibliotheca identifier are exactly equivalent.
        bibliotheca_identifier.equivalent_to(self.api.source, isbn, strength=1)

        # Log the event.
        start = start_time or CirculationEvent.NO_DATE

        # Make sure the effects of the event reported by Bibliotheca
        # are made visible on the LicensePool and turned into
        # analytics events. This is not 100% reliable, but it
        # should be mostly accurate, and the BibliothecaCirculationSweep
        # will periodically correct the errors.
        license_pool.update_availability_from_delta(internal_event_type,
                                                    start_time, 1,
                                                    self.analytics)

        if is_new:
            # This is our first time seeing this LicensePool. Log its
            # occurance as a separate event.
            license_pool.collect_analytics_event(
                self.analytics, CirculationEvent.DISTRIBUTOR_TITLE_ADD,
                license_pool.last_checked or start_time, 0, 1)
        title = edition.title or "[no title]"
        self.log.info("%r %s: %s", start_time, title, internal_event_type)
        return start_time
Пример #12
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    def handle_event(self, threem_id, isbn, foreign_patron_id, start_time,
                     end_time, internal_event_type):
        # Find or lookup the LicensePool for this event.
        license_pool, is_new = LicensePool.for_foreign_id(
            self._db, self.api.source, Identifier.THREEM_ID, threem_id)

        if is_new:
            # Immediately acquire bibliographic coverage for this book.
            # This will set the DistributionMechanisms and make the
            # book presentation-ready. However, its circulation information
            # might not be up to date until we process some more events.
            record = self.bibliographic_coverage_provider.ensure_coverage(
                license_pool.identifier, force=True)

        threem_identifier = license_pool.identifier
        isbn, ignore = Identifier.for_foreign_id(self._db, Identifier.ISBN,
                                                 isbn)

        edition, ignore = Edition.for_foreign_id(self._db, self.api.source,
                                                 Identifier.THREEM_ID,
                                                 threem_id)

        # The ISBN and the 3M identifier are exactly equivalent.
        threem_identifier.equivalent_to(self.api.source, isbn, strength=1)

        # Log the event.
        event, was_new = get_one_or_create(self._db,
                                           CirculationEvent,
                                           license_pool=license_pool,
                                           type=internal_event_type,
                                           start=start_time,
                                           foreign_patron_id=foreign_patron_id,
                                           create_method_kwargs=dict(
                                               delta=1, end=end_time))

        # If this is our first time seeing this LicensePool, log its
        # occurance as a separate event
        if is_new:
            event = get_one_or_create(
                self._db,
                CirculationEvent,
                type=CirculationEvent.DISTRIBUTOR_TITLE_ADD,
                license_pool=license_pool,
                create_method_kwargs=dict(
                    start=license_pool.last_checked or start_time,
                    delta=1,
                    end=license_pool.last_checked or end_time,
                ))
        title = edition.title or "[no title]"
        self.log.info("%r %s: %s", start_time, title, internal_event_type)
        return start_time
Пример #13
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    def handle_event(self, threem_id, isbn, foreign_patron_id,
                     start_time, end_time, internal_event_type):
        # Find or lookup the LicensePool for this event.
        license_pool, is_new = LicensePool.for_foreign_id(
            self._db, self.api.source, Identifier.THREEM_ID, threem_id)

        if is_new:
            # Immediately acquire bibliographic coverage for this book.
            # This will set the DistributionMechanisms and make the
            # book presentation-ready. However, its circulation information
            # might not be up to date until we process some more events.
            record = self.bibliographic_coverage_provider.ensure_coverage(
                license_pool.identifier, force=True
            )

        threem_identifier = license_pool.identifier
        isbn, ignore = Identifier.for_foreign_id(
            self._db, Identifier.ISBN, isbn)

        edition, ignore = Edition.for_foreign_id(
            self._db, self.api.source, Identifier.THREEM_ID, threem_id)

        # The ISBN and the 3M identifier are exactly equivalent.
        threem_identifier.equivalent_to(self.api.source, isbn, strength=1)

        # Log the event.
        event, was_new = get_one_or_create(
            self._db, CirculationEvent, license_pool=license_pool,
            type=internal_event_type, start=start_time,
            foreign_patron_id=foreign_patron_id,
            create_method_kwargs=dict(delta=1,end=end_time)
            )

        # If this is our first time seeing this LicensePool, log its
        # occurance as a separate event
        if is_new:
            event = get_one_or_create(
                self._db, CirculationEvent,
                type=CirculationEvent.TITLE_ADD,
                license_pool=license_pool,
                create_method_kwargs=dict(
                    start=license_pool.last_checked or start_time,
                    delta=1,
                    end=license_pool.last_checked or end_time,
                )
            )
        title = edition.title or "[no title]"
        self.log.info("%r %s: %s", start_time, title, internal_event_type)
        return start_time
Пример #14
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    def test_register_equivalency(self):
        data_source = DataSource.lookup(self._db, DataSource.GUTENBERG)
        id = "549"

        # We've got a record.
        record, was_new = Edition.for_foreign_id(self._db, data_source,
                                                 Identifier.GUTENBERG_ID, id)

        # Then we look it up and discover another identifier for it.
        data_source_2 = DataSource.lookup(self._db, DataSource.OCLC)
        record2, was_new = Edition.for_foreign_id(self._db, data_source_2,
                                                  Identifier.OCLC_NUMBER, "22")

        eq = record.primary_identifier.equivalent_to(
            data_source_2, record2.primary_identifier, 1)

        assert eq.input == record.primary_identifier
        assert eq.output == record2.primary_identifier
        assert eq.data_source == data_source_2

        assert [eq] == record.primary_identifier.equivalencies

        assert set([record,
                    record2]) == set(record.equivalent_editions().all())
Пример #15
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    def test_finalize_license_pool(self):

        provider_no_presentation_ready = self._provider(
            presentation_ready_on_success=False)
        provider_presentation_ready = self._provider(
            presentation_ready_on_success=True)
        identifier = self._identifier()
        license_source = DataSource.lookup(self._db, DataSource.GUTENBERG)
        data_source = DataSource.lookup(self._db, DataSource.OA_CONTENT_SERVER)

        # Here's a LicensePool with no presentation edition.
        pool, is_new = LicensePool.for_foreign_id(self._db, license_source,
                                                  identifier.type,
                                                  identifier.identifier)
        eq_(None, pool.presentation_edition)

        # Calling finalize_license_pool() here won't do much.
        provider_no_presentation_ready.finalize_license_pool(pool)

        # A presentation edition has been created for the LicensePool,
        # but it has no title (in fact it has no data at all), so no
        # Work was created.
        eq_(None, pool.presentation_edition.title)
        eq_(0, self._db.query(Work).count())

        # Here's an Edition for the same book as the LicensePool but
        # from a different data source.
        edition, is_new = Edition.for_foreign_id(self._db, data_source,
                                                 identifier.type,
                                                 identifier.identifier)
        edition.title = self._str

        # Although Edition and LicensePool share an identifier, they
        # are not otherwise related.
        eq_(None, pool.presentation_edition.title)

        # finalize_license_pool() will create a Work and update the
        # LicensePool's presentation edition, based on the brand-new
        # Edition.
        provider_no_presentation_ready.finalize_license_pool(pool)
        work = pool.work
        eq_(edition.title, pool.presentation_edition.title)
        eq_(False, work.presentation_ready)

        # If the provider is configured to do so, finalize_license_pool()
        # will also set the Work as presentation-ready.
        provider_presentation_ready.finalize_license_pool(pool)
        eq_(True, work.presentation_ready)
Пример #16
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    def update_licensepool_with_book_info(self, book, license_pool, is_new):
        """Update a book's LicensePool with information from a JSON
        representation of its circulation info.

        Also creates an Edition and gives it very basic bibliographic
        information (the title), if possible.
        """
        circulation = OverdriveRepresentationExtractor.book_info_to_circulation(
            book
        )
        circulation_changed = circulation.update(license_pool, is_new)

        edition, ignore = Edition.for_foreign_id(
            self._db, self.source, license_pool.identifier.type,
            license_pool.identifier.identifier)
        edition.title = edition.title or book.get('title')
        if is_new:
            license_pool.open_access = False
            self.log.info("New Overdrive book discovered: %r", edition)
        return license_pool, is_new, circulation_changed
Пример #17
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    def test_finalize_license_pool(self):

        identifier = self._identifier()
        license_source = DataSource.lookup(self._db, DataSource.GUTENBERG)
        data_source = DataSource.lookup(self._db, DataSource.OA_CONTENT_SERVER)

        # Here's a LicensePool with no presentation edition.
        pool, is_new = LicensePool.for_foreign_id(
            self._db,
            license_source,
            identifier.type,
            identifier.identifier,
            collection=self._default_collection)
        eq_(None, pool.presentation_edition)

        # Here's an Edition for the same book as the LicensePool but
        # from a different data source.
        edition, is_new = Edition.for_foreign_id(self._db, data_source,
                                                 identifier.type,
                                                 identifier.identifier)
        edition.title = self._str

        # Although Edition and LicensePool share an identifier, they
        # are not otherwise related.
        eq_(None, pool.presentation_edition)

        # finalize_license_pool() will create a Work and update the
        # LicensePool's presentation edition, based on the brand-new
        # Edition.
        lookup = MockSimplifiedOPDSLookup(self._url)
        provider = ContentServerBibliographicCoverageProvider(
            self._default_collection, lookup)
        provider.finalize_license_pool(pool)
        work = pool.work
        eq_(edition.title, pool.presentation_edition.title)
        eq_(True, work.presentation_ready)
Пример #18
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    def _extract_publication_metadata(self, feed, publication, data_source_name):
        """Extract a Metadata object from webpub-manifest-parser's publication.

        :param publication: Feed object
        :type publication: opds2_ast.OPDS2Feed

        :param publication: Publication object
        :type publication: opds2_ast.OPDS2Publication

        :param data_source_name: Data source's name
        :type data_source_name: str

        :return: Publication's metadata
        :rtype: Metadata
        """
        metadata = super(ODL2Importer, self)._extract_publication_metadata(
            feed, publication, data_source_name
        )
        formats = []
        licenses = []
        medium = None

        with self._get_configuration(self._db) as configuration:
            skipped_license_formats = configuration.skipped_license_formats

            if skipped_license_formats:
                skipped_license_formats = set(skipped_license_formats)

        if publication.licenses:
            for odl_license in publication.licenses:
                identifier = odl_license.metadata.identifier
                checkout_link = first_or_default(
                    odl_license.links.get_by_rel(OPDS2LinkRelationsRegistry.BORROW.key)
                )
                if checkout_link:
                    checkout_link = checkout_link.href

                license_info_document_link = first_or_default(
                    odl_license.links.get_by_rel(OPDS2LinkRelationsRegistry.SELF.key)
                )
                if license_info_document_link:
                    license_info_document_link = license_info_document_link.href

                expires = (
                    to_utc(odl_license.metadata.terms.expires)
                    if odl_license.metadata.terms
                    else None
                )
                concurrency = (
                    int(odl_license.metadata.terms.concurrency)
                    if odl_license.metadata.terms
                    else None
                )

                if not license_info_document_link:
                    parsed_license = None
                else:
                    parsed_license = ODLImporter.get_license_data(
                        license_info_document_link,
                        checkout_link,
                        identifier,
                        expires,
                        concurrency,
                        self.http_get,
                    )

                if parsed_license is not None:
                    licenses.append(parsed_license)

                # DPLA feed doesn't have information about a DRM protection used for audiobooks.
                # We want to try to extract that information from the License Info Document it's present there.
                license_formats = set(odl_license.metadata.formats)
                if parsed_license and parsed_license.content_types:
                    license_formats |= set(parsed_license.content_types)

                for license_format in license_formats:
                    if (
                        skipped_license_formats
                        and license_format in skipped_license_formats
                    ):
                        continue

                    if not medium:
                        medium = Edition.medium_from_media_type(license_format)

                    if license_format in ODLImporter.LICENSE_FORMATS:
                        # Special case to handle DeMarque audiobooks which
                        # include the protection in the content type
                        drm_schemes = [
                            ODLImporter.LICENSE_FORMATS[license_format][
                                ODLImporter.DRM_SCHEME
                            ]
                        ]
                        license_format = ODLImporter.LICENSE_FORMATS[license_format][
                            ODLImporter.CONTENT_TYPE
                        ]
                    else:
                        drm_schemes = (
                            odl_license.metadata.protection.formats
                            if odl_license.metadata.protection
                            else []
                        )

                    for drm_scheme in drm_schemes or [None]:
                        formats.append(
                            FormatData(
                                content_type=license_format,
                                drm_scheme=drm_scheme,
                                rights_uri=RightsStatus.IN_COPYRIGHT,
                            )
                        )

        metadata.circulation.licenses = licenses
        metadata.circulation.licenses_owned = None
        metadata.circulation.licenses_available = None
        metadata.circulation.licenses_reserved = None
        metadata.circulation.patrons_in_hold_queue = None
        metadata.circulation.formats.extend(formats)
        metadata.medium = medium

        return metadata
Пример #19
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    def test_recursively_equivalent_identifiers(self):

        # We start with a Gutenberg book.
        gutenberg = DataSource.lookup(self._db, DataSource.GUTENBERG)
        record, ignore = Edition.for_foreign_id(self._db, gutenberg,
                                                Identifier.GUTENBERG_ID, "100")
        gutenberg_id = record.primary_identifier

        # We use OCLC Classify to do a title/author lookup.
        oclc = DataSource.lookup(self._db, DataSource.OCLC)
        search_id, ignore = Identifier.for_foreign_id(self._db,
                                                      Identifier.OCLC_WORK,
                                                      "60010")
        gutenberg_id.equivalent_to(oclc, search_id, 1)

        # The title/author lookup associates the search term with two
        # different OCLC Numbers.
        oclc_id, ignore = Identifier.for_foreign_id(self._db,
                                                    Identifier.OCLC_NUMBER,
                                                    "9999")
        oclc_id_2, ignore = Identifier.for_foreign_id(self._db,
                                                      Identifier.OCLC_NUMBER,
                                                      "1000")

        search_id.equivalent_to(oclc, oclc_id, 1)
        search_id.equivalent_to(oclc, oclc_id_2, 1)

        # We then use OCLC Linked Data to connect one of the OCLC
        # Numbers with an ISBN.
        linked_data = DataSource.lookup(self._db, DataSource.OCLC_LINKED_DATA)
        isbn_id, ignore = Identifier.for_foreign_id(self._db, Identifier.ISBN,
                                                    "900100434X")
        oclc_id.equivalent_to(linked_data, isbn_id, 1)

        # As it turns out, we have an Overdrive work record...
        overdrive = DataSource.lookup(self._db, DataSource.OVERDRIVE)
        overdrive_record, ignore = Edition.for_foreign_id(
            self._db, overdrive, Identifier.OVERDRIVE_ID, "{111-222}")
        overdrive_id = overdrive_record.primary_identifier

        # ...which is tied (by Overdrive) to the same ISBN.
        overdrive_id.equivalent_to(overdrive, isbn_id, 1)

        # Finally, here's a completely unrelated Edition, which
        # will not be showing up.
        gutenberg2, ignore = Edition.for_foreign_id(self._db, gutenberg,
                                                    Identifier.GUTENBERG_ID,
                                                    "200")
        gutenberg2.title = "Unrelated Gutenberg record."

        levels = [
            record.equivalent_identifiers(policy=PresentationCalculationPolicy(
                equivalent_identifier_levels=i)) for i in range(0, 5)
        ]

        # At level 0, the only identifier found is the Gutenberg ID.
        assert set([gutenberg_id]) == set(levels[0])

        # At level 1, we pick up the title/author lookup.
        assert set([gutenberg_id, search_id]) == set(levels[1])

        # At level 2, we pick up the title/author lookup and the two
        # OCLC Numbers.
        assert set([gutenberg_id, search_id, oclc_id,
                    oclc_id_2]) == set(levels[2])

        # At level 3, we also pick up the ISBN.
        assert set([gutenberg_id, search_id, oclc_id, oclc_id_2,
                    isbn_id]) == set(levels[3])

        # At level 4, the recursion starts to go in the other
        # direction: we pick up the Overdrive ID that's equivalent to
        # the same ISBN as the OCLC Number.
        assert set([
            gutenberg_id, search_id, oclc_id, oclc_id_2, isbn_id, overdrive_id
        ]) == set(levels[4])