Demo: simplify resolve_user to a plain previous-state lookup

demo/main.py

@@ -7,7 +7,7 @@ from pathlib import Path
 import msgspec
 
 from kanta import Kanta
-from kanta.callbacks import DictPost, DictPre
+from kanta.callbacks import DictPre
 from kanta.logging import configure_logging
 
 
@@ -47,18 +47,11 @@ kanta_v1 = Kanta(filename, Data(), migrations=sys.modules[__name__])
 
 
 @kanta_v1.logfmt
-def resolve_user(
-    value: str, path: str, previous: DictPre, current: DictPost
-) -> str | None:
+def resolve_user(value: str, path: str, previous: DictPre) -> str | None:
     """Resolve user ids to names from the database state itself."""
     if path != "$user" and not path.startswith("users."):
         return None
-    # Post-change state first, then pre-change (deleted users are only there).
-    for state in (current, previous):
-        name = state.get("users", {}).get(value, {}).get("name")
-        if name:
-            return name
-    return None
+    return previous.get("users", {}).get(value, {}).get("name")
 
 
 async def main() -> None:
@@ -92,18 +85,13 @@ async def main() -> None:
     )
     async with kanta_v1 as kanta:
         with kanta.transaction(
-            action="import", user="userid001", logdiff=False
+            action="update", user="userid002", extra=filename.name
         ) as data:
-            data.total = 3
+            data.total += 1
 
         with kanta.transaction(action="delete", user="userid002") as data:
             del data.users["userid001"]
 
-        with kanta.transaction(
-            action="update", user="userid002", extra=filename.name
-        ) as data:
-            data.total = 4
-
 
 # Fake clock for deterministic timestamps
 _now = datetime(2027, 1, 1, tzinfo=UTC)