111 lines
3.1 KiB
Python
111 lines
3.1 KiB
Python
#!/usr/bin/env -S uv run
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import asyncio
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import sys
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from datetime import UTC, datetime, timedelta
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from pathlib import Path
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import msgspec
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from kanta import Kanta
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from kanta.callbacks import DictPre
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from kanta.logging import configure_logging
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filename = Path(__file__).with_name("demo.kantadb")
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# For demonstration purposes, we use "original v0" and "modified v1" in this same script
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# Normally your app would only have the latest supported data model
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class Data(msgspec.Struct): # type: ignore - intentionally redefined later
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users: dict[str, dict] = {}
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counter: int = 0
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kanta_v0 = Kanta(filename, Data())
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@kanta_v0.bootstrap
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def bootstrap(data: Data) -> None:
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"""Create the initial admin user."""
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data.users["userid001"] = {"name": "Alice", "role": "admin"}
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# Redefinition to simulate new version
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class Data(msgspec.Struct):
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users: dict[str, dict] = {}
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total: int = 0 # Replaces old counter field
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lang: str = "en" # New field
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def migrate_v1(d: dict) -> None:
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"""Rename counter to total"""
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d["total"] = d["counter"]
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kanta_v1 = Kanta(filename, Data(), migrations=sys.modules[__name__])
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@kanta_v1.logfmt
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def resolve_user(value: str, path: str, previous: DictPre) -> str | None:
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"""Resolve user ids to names from the database state itself."""
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if path != "$user" and not path.startswith("users."):
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return None
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return previous.get("users", {}).get(value, {}).get("name")
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async def main() -> None:
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filename.unlink(missing_ok=True)
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print("# Database creation with v0 schema and basic ops, pretty logs")
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# Open and close automatically; you can also `await kanta.open()` instead
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async with kanta_v0 as kanta:
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with kanta.transaction(action="create", user="userid001") as data:
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data.users["userid002"] = {"name": "Bob", "role": "user"}
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with kanta.transaction(action="update", user="userid001") as data:
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data.users["userid002"]["role"] = "editor"
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data.counter = 1
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# Display-only extra string, appended after the action.
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with kanta.transaction(
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action="export", user="userid002", extra="extra info"
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) as data:
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data.counter = 2
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try:
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with kanta.transaction(action="reset") as data:
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data.counter = 99
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raise ValueError("simulated failure")
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except ValueError:
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print(f"# Reading does not need transaction: {data.counter=}", flush=True)
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print(
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"\n# A later version of our application with new data model, migrations and logfmt"
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)
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async with kanta_v1 as kanta:
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with kanta.transaction(
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action="update", user="userid002", extra=filename.name
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) as data:
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data.total += 1
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with kanta.transaction(action="delete", user="userid002") as data:
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del data.users["userid001"]
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# Fake clock for deterministic timestamps
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_now = datetime(2027, 1, 1, tzinfo=UTC)
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@kanta_v0.clock
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@kanta_v1.clock
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def fake_clock() -> datetime:
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global _now
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_now += timedelta(hours=1)
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return _now
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if __name__ == "__main__":
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configure_logging()
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asyncio.run(main())
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