Propagate rename_table to inbound ForeignKey references in the schema snapshot

piccolo/apps/migrations/auto/schema_snapshot.py

@@ -4,6 +4,8 @@
 
 from piccolo.apps.migrations.auto.diffable_table import DiffableTable
 from piccolo.apps.migrations.auto.migration_manager import MigrationManager
+from piccolo.columns.column_types import ForeignKey
+from piccolo.table import Table, create_table_class
 
 
 @dataclass
@@ -49,6 +51,35 @@ def get_snapshot(self) -> list[DiffableTable]:
                         table.tablename = rename_table.new_tablename
                         break
 
+                # Foreign keys on other tables still point at the old table
+                # class, so the snapshot would keep diffing against the
+                # renamed model and emit an ``alter_column`` for each of them
+                # on every ``--auto`` run.
+                for table in tables:
+                    for column in table.columns:
+                        if not isinstance(column, ForeignKey):
+                            continue
+                        references = column._meta.params.get("references")
+                        if not (
+                            isinstance(references, type)
+                            and issubclass(references, Table)
+                            and references.__name__
+                            == rename_table.old_class_name
+                            and references._meta.tablename
+                            == rename_table.old_tablename
+                        ):
+                            continue
+                        renamed = create_table_class(
+                            class_name=rename_table.new_class_name,
+                            bases=(references,),
+                            class_kwargs={
+                                "tablename": rename_table.new_tablename,
+                                "schema": references._meta.schema,
+                            },
+                        )
+                        column._meta.params["references"] = renamed
+                        column._foreign_key_meta.references = renamed
+
             for change_table_schema in manager.change_table_schemas:
                 for table in tables:
                     if table.tablename == change_table_schema.tablename:

tests/apps/migrations/auto/test_schema_snapshot.py

@@ -1,7 +1,13 @@
 from unittest import TestCase
 
-from piccolo.apps.migrations.auto import MigrationManager, SchemaSnapshot
+from piccolo.apps.migrations.auto import (
+    DiffableTable,
+    MigrationManager,
+    SchemaSnapshot,
+)
+from piccolo.columns.column_types import ForeignKey
 from piccolo.constraints import Unique
+from piccolo.table import Table
 
 
 class TestSchemaSnaphot(TestCase):
@@ -64,6 +70,62 @@ def test_rename_table(self):
         self.assertTrue(snapshot[0].class_name == "Performer")
         self.assertTrue(snapshot[0].tablename == "performer")
 
+    def test_rename_table_updates_foreign_key_references(self):
+        """
+        Renaming a table must also update the foreign keys on other tables
+        which point at it, otherwise the snapshot keeps diffing against the
+        renamed model and emits an ``alter_column`` on every ``--auto`` run.
+        """
+
+        class Band(Table, tablename="band"):
+            pass
+
+        manager_1 = MigrationManager()
+        manager_1.add_table(class_name="Band", tablename="band")
+        manager_1.add_table(class_name="Concert", tablename="concert")
+        manager_1.add_column(
+            table_class_name="Concert",
+            tablename="concert",
+            column_name="band",
+            column_class_name="ForeignKey",
+            column_class=ForeignKey,
+            params={"references": Band},
+        )
+
+        manager_2 = MigrationManager()
+        manager_2.rename_table(
+            old_class_name="Band",
+            old_tablename="band",
+            new_class_name="Performer",
+            new_tablename="performer",
+        )
+
+        schema_snapshot = SchemaSnapshot(managers=[manager_1, manager_2])
+        concert = schema_snapshot.get_table_from_snapshot("Concert")
+        references = concert.columns[0]._meta.params["references"]
+
+        self.assertEqual(references.__name__, "Performer")
+        self.assertEqual(references._meta.tablename, "performer")
+
+        # The snapshot now agrees with the renamed model, so there is
+        # nothing left to migrate.
+        class Performer(Table, tablename="performer"):
+            pass
+
+        class Concert(Table, tablename="concert"):
+            band = ForeignKey(Performer)
+
+        delta = (
+            DiffableTable(
+                class_name="Concert",
+                tablename="concert",
+                columns=[Concert.band],
+            )
+            - concert
+        )
+
+        self.assertEqual(delta.alter_columns, [])
+
     def test_add_column(self):
         """
         Test adding columns.