Generate likely followers url for existing users

bookwyrm/migrations/0086_auto_20210828_1724.py

@@ -3,24 +3,47 @@
 import bookwyrm.models.fields
 from django.conf import settings
 from django.db import migrations, models
+from django.db.models import F, Value, CharField
+from django.db.models.functions import Concat
+
+
+def forwards_func(apps, schema_editor):
+    """generate followers url"""
+    db_alias = schema_editor.connection.alias
+    apps.get_model("bookwyrm", "User").objects.using(db_alias).annotate(
+        generated_url=Concat(
+            F("remote_id"), Value("/followers"), output_field=CharField()
+        )
+    ).update(followers_url=models.F("generated_url"))
+
+
+def reverse_func(apps, schema_editor):
+    """noop"""
 
 
 class Migration(migrations.Migration):
 
     dependencies = [
-        ('bookwyrm', '0085_user_saved_lists'),
+        ("bookwyrm", "0085_user_saved_lists"),
     ]
 
     operations = [
         migrations.AddField(
-            model_name='user',
-            name='followers_url',
-            field=bookwyrm.models.fields.CharField(default='/followers', max_length=255),
+            model_name="user",
+            name="followers_url",
+            field=bookwyrm.models.fields.CharField(
+                default="/followers", max_length=255
+            ),
             preserve_default=False,
         ),
+        migrations.RunPython(forwards_func, reverse_func),
         migrations.AlterField(
-            model_name='user',
-            name='followers',
-            field=models.ManyToManyField(through='bookwyrm.UserFollows', to=settings.AUTH_USER_MODEL),
+            model_name="user",
+            name="followers",
+            field=models.ManyToManyField(
+                related_name="following",
+                through="bookwyrm.UserFollows",
+                to=settings.AUTH_USER_MODEL,
+            ),
         ),
     ]