use right alembic downgrade when downgrading

-1 is not always the right choice, e.g. when the previous update script
has the same alembic version. Therefore, we actually need to do the
effort to track the "previous alembic" version.

1 files changed, 18 insertions, 4 deletions

diff --git a/fietsboek/updater/__init__.py b/fietsboek/updater/__init__.py
index 3611e9f..b136a6c 100644
--- a/fietsboek/updater/__init__.py
+++ b/fietsboek/updater/__init__.py
@@ -86,8 +86,20 @@ class Updater:
         # Ensure that each script has an entry
         self.backward_dependencies = {script.id: [] for script in self.scripts.values()}
         for script in self.scripts.values():
+            down_alembic = None
             for prev_id in script.previous:
                 self.backward_dependencies[prev_id].append(script.id)
+                possible_alembic = self.scripts[prev_id].alembic_version
+                if down_alembic is None:
+                    down_alembic = possible_alembic
+                elif down_alembic != possible_alembic:
+                    LOGGER.error(
+                        "Invalid update graph - two different down alembics for script %s",
+                        script.id,
+                    )
+                    raise ValueError(f"Two alembic downgrades for {script.id}")
+                down_alembic = possible_alembic
+            script.down_alembic = down_alembic
 
     def exists(self, revision_id):
         """Checks if the revision with the given ID exists.
@@ -291,6 +303,7 @@ class UpdateScript:
         self.module = importlib.util.module_from_spec(spec)  # type: ignore
         assert self.module
         exec(source, self.module.__dict__)  # pylint: disable=exec-used
+        self.down_alembic = None
 
     def __repr__(self):
         return f"<{__name__}.{self.__class__.__name__} name={self.name!r} id={self.id!r}>"
@@ -355,10 +368,11 @@ class UpdateScript:
         """
         LOGGER.info("[down] Running pre-alembic task for %s", self.id)
         self.module.Down().pre_alembic(config)
-        LOGGER.info("[down] Running alembic downgrade for %s to %s", self.id, self.alembic_version)
-        alembic.command.downgrade(alembic_config, "-1")
-        LOGGER.info("[down] Running post-alembic task for %s", self.id)
-        self.module.Down().post_alembic(config)
+        if self.down_alembic:
+            LOGGER.info("[down] Running alembic downgrade for %s to %s", self.id, self.down_alembic)
+            alembic.command.downgrade(alembic_config, self.down_alembic)
+            LOGGER.info("[down] Running post-alembic task for %s", self.id)
+            self.module.Down().post_alembic(config)
 
 
 def _filename_to_modname(name):