Refactor removal of deprecated features while preserving database state

dojo/db_migrations/0265_remove_stub_finding.py

@@ -1,8 +1,10 @@
-"""Remove the Stub Findings feature.
+"""Remove the Stub Findings feature (state only).
 
-Drops the ``Stub_Finding`` model. Stub Findings was deprecated in 2.57.0 and
-is end-of-life in 2.59. The model has no inbound foreign keys, so the
-deletion is self-contained.
+Drops the ``Stub_Finding`` model from Django's state but leaves the
+``dojo_stub_finding`` table in place so a downgrade to a release that still
+defines the model keeps its data. Stub Findings was deprecated in 2.57.0 and
+is end-of-life in 2.59. The model has no inbound foreign keys, so the removal
+is self-contained.
 
 Note: rebase the filename and the ``dependencies`` tuple to point at
 whatever the latest migration is at merge time if another migration has
@@ -19,7 +21,14 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
-        migrations.DeleteModel(
-            name="Stub_Finding",
+        migrations.SeparateDatabaseAndState(
+            # State only: forget the model so it no longer has to be defined
+            # in dojo/models.py. database_operations is intentionally empty so
+            # the dojo_stub_finding table is preserved for downgrades.
+            state_operations=[
+                migrations.DeleteModel(
+                    name="Stub_Finding",
+                ),
+            ],
         ),
     ]

dojo/db_migrations/0266_remove_credential_manager.py

@@ -1,9 +1,11 @@
-"""Remove the Credential Manager feature.
+"""Remove the Credential Manager feature (state only).
 
-Drops the `Cred_User`, `Cred_Mapping`, and `Cred_UserEvent` models, removes
-the pghistory triggers that wrote into the latter, and removes the
-`enable_credentials` switch from System_Settings. The Credential Manager
-feature was deprecated in 2.57.0 and is end-of-life in 2.59.
+Removes the `Cred_User`, `Cred_Mapping`, and `Cred_UserEvent` models, their
+pghistory triggers, and the `enable_credentials` switch from System_Settings
+from Django's state, but leaves the underlying tables, columns, and triggers
+in the database so a downgrade to a release that still defines them keeps its
+data. The Credential Manager feature was deprecated in 2.57.0 and is
+end-of-life in 2.59.
 """
 
 import pgtrigger.migrations
@@ -17,36 +19,56 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
-        # Remove pghistory triggers that mirror Cred_User changes into
-        # Cred_UserEvent. Triggers must be dropped before the source / event
-        # tables can be removed.
-        pgtrigger.migrations.RemoveTrigger(
-            model_name="cred_user",
-            name="insert_insert",
+        # State only: forget the models and their triggers so they no longer
+        # have to be defined in dojo/models.py. There are no database_operations
+        # so the dojo_cred_user, dojo_cred_mapping, and dojo_cred_userevent
+        # tables and the cred_user pghistory triggers are preserved for
+        # downgrades.
+        migrations.SeparateDatabaseAndState(
+            state_operations=[
+                # Drop the pghistory triggers from state before the model they
+                # hang off of is removed.
+                pgtrigger.migrations.RemoveTrigger(
+                    model_name="cred_user",
+                    name="insert_insert",
+                ),
+                pgtrigger.migrations.RemoveTrigger(
+                    model_name="cred_user",
+                    name="update_update",
+                ),
+                pgtrigger.migrations.RemoveTrigger(
+                    model_name="cred_user",
+                    name="delete_delete",
+                ),
+                # Cred_UserEvent FKs Cred_User; Cred_Mapping FKs Cred_User too,
+                # so both come out of state before Cred_User itself.
+                migrations.DeleteModel(
+                    name="Cred_UserEvent",
+                ),
+                migrations.DeleteModel(
+                    name="Cred_Mapping",
+                ),
+                migrations.DeleteModel(
+                    name="Cred_User",
+                ),
+            ],
         ),
-        pgtrigger.migrations.RemoveTrigger(
-            model_name="cred_user",
-            name="update_update",
-        ),
-        pgtrigger.migrations.RemoveTrigger(
-            model_name="cred_user",
-            name="delete_delete",
-        ),
-        # Drop the audit/event table (FKs from Cred_UserEvent → Cred_User get
-        # cleaned up automatically as part of DeleteModel).
-        migrations.DeleteModel(
-            name="Cred_UserEvent",
-        ),
-        # Cred_Mapping holds an FK to Cred_User and must be dropped first.
-        migrations.DeleteModel(
-            name="Cred_Mapping",
-        ),
-        migrations.DeleteModel(
-            name="Cred_User",
-        ),
-        # The UI toggle no longer has anything to gate.
-        migrations.RemoveField(
-            model_name="system_settings",
-            name="enable_credentials",
+        # Drop the enable_credentials field from state but keep the column for
+        # downgrades. The model no longer supplies a value on INSERT, so give
+        # the column a server-side default (the field defaulted to True) to
+        # keep new System_Settings rows satisfying its NOT NULL constraint.
+        migrations.SeparateDatabaseAndState(
+            state_operations=[
+                migrations.RemoveField(
+                    model_name="system_settings",
+                    name="enable_credentials",
+                ),
+            ],
+            database_operations=[
+                migrations.RunSQL(
+                    sql="ALTER TABLE dojo_system_settings ALTER COLUMN enable_credentials SET DEFAULT true;",
+                    reverse_sql="ALTER TABLE dojo_system_settings ALTER COLUMN enable_credentials DROP DEFAULT;",
+                ),
+            ],
         ),
     ]