Clear unused editions with poor metadata

bookwyrm/management/commands/remove_editions.py

@@ -0,0 +1,34 @@
+''' PROCEED WITH CAUTION: this permanently deletes book data '''
+from django.core.management.base import BaseCommand
+from django.db.models import Count, Q
+from bookwyrm import models
+
+
+def remove_editions():
+    ''' combine duplicate editions and update related models '''
+    # not in use
+    filters = {'%s__isnull' % r.name: True \
+        for r in models.Edition._meta.related_objects}
+    # no cover, no identifying fields
+    filters['cover'] = ''
+    null_fields = {'%s__isnull' % f: True for f in \
+        ['isbn_10', 'isbn_13', 'oclc_number']}
+
+    editions = models.Edition.objects.filter(
+        Q(languages=[]) | Q(languages__contains=['English']),
+        **filters, **null_fields
+    ).annotate(Count('parent_work__editions')).filter(
+        # mustn't be the only edition for the work
+        parent_work__editions__count__gt=1
+    )
+    print(editions.count())
+    editions.delete()
+
+
+class Command(BaseCommand):
+    ''' dedplucate allllll the book data models '''
+    help = 'merges duplicate book data'
+    # pylint: disable=no-self-use,unused-argument
+    def handle(self, *args, **options):
+        ''' run deudplications '''
+        remove_editions()