apps/modules: Populate existing Items with content-type values (#1833)

Author: glanzel

adhocracy4/modules/migrations/0010_populate_item_polymorphic_ctype.py

@@ -0,0 +1,69 @@
+# Generated manually to backfill polymorphic_ctype on existing items.
+from django.db import migrations
+
+
+def populate_polymorphic_ctypes(apps, schema_editor):
+    Item = apps.get_model("a4modules", "Item")
+    ContentType = apps.get_model("contenttypes", "ContentType")
+    db_alias = schema_editor.connection.alias
+
+    def get_parent_link(model):
+        for field in model._meta.fields:
+            remote_field = getattr(field, "remote_field", None)
+            if remote_field and remote_field.parent_link:
+                return field
+        return None
+
+    # Update all known subclasses first.
+    for model in apps.get_models():
+        if model is Item:
+            continue
+        try:
+            is_item_subclass = issubclass(model, Item)
+        except TypeError:
+            continue
+        if not is_item_subclass:
+            continue
+
+        parent_link_field = get_parent_link(model)
+        if not parent_link_field:
+            continue
+
+        content_type = ContentType.objects.db_manager(db_alias).get_for_model(
+            model, for_concrete_model=False
+        )
+        item_ids = model._default_manager.using(db_alias).values_list(
+            parent_link_field.attname, flat=True
+        )
+        (
+            Item.objects.using(db_alias)
+            .filter(polymorphic_ctype__isnull=True, pk__in=item_ids)
+            .update(polymorphic_ctype=content_type)
+        )
+
+    # Any remaining items fallback to the base Item content type.
+    base_ct = ContentType.objects.db_manager(db_alias).get_for_model(
+        Item, for_concrete_model=False
+    )
+    (
+        Item.objects.using(db_alias)
+        .filter(polymorphic_ctype__isnull=True)
+        .update(polymorphic_ctype=base_ct)
+    )
+
+
+def remove_polymorphic_ctypes(apps, schema_editor):
+    Item = apps.get_model("a4modules", "Item")
+    Item.objects.using(schema_editor.connection.alias).update(polymorphic_ctype=None)
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("a4modules", "0009_alter_item_options_item_polymorphic_ctype"),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            populate_polymorphic_ctypes, reverse_code=remove_polymorphic_ctypes
+        ),
+    ]