Add shelved_date field and populate it on import

bookwyrm/migrations/0078_add_shelved_date.py

@@ -0,0 +1,34 @@
+# Generated by Django 3.2.4 on 2021-07-03 08:25
+
+from django.db import migrations, models
+import django.utils.timezone
+
+
+def copy_created_date(app_registry, schema_editor):
+    db_alias = schema_editor.connection.alias
+    ShelfBook = app_registry.get_model("bookwyrm", "ShelfBook")
+    ShelfBook.objects.all().update(shelved_date=models.F("created_date"))
+
+
+def do_nothing(app_registry, schema_editor):
+    pass
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("bookwyrm", "0077_auto_20210623_2155"),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name="shelfbook",
+            options={"ordering": ("-shelved_date",)},
+        ),
+        migrations.AddField(
+            model_name="shelfbook",
+            name="shelved_date",
+            field=models.DateTimeField(default=django.utils.timezone.now),
+        ),
+        migrations.RunPython(copy_created_date, reverse_code=do_nothing),
+    ]