init

backend/app/db.py

@@ -0,0 +1,62 @@
+"""Database engine and session plumbing.
+
+Synchronous SQLAlchemy on purpose: the background scheduler, the Telegram
+polling bot and the request handlers all touch the same tables, and one boring
+threadsafe sessionmaker is far easier to reason about than three event loops.
+FastAPI runs plain `def` endpoints in a threadpool, so nothing blocks.
+"""
+
+from __future__ import annotations
+
+from collections.abc import Iterator
+from contextlib import contextmanager
+
+from sqlalchemy import create_engine
+from sqlalchemy.orm import DeclarativeBase, Session, sessionmaker
+
+from app.config import env_settings
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+def _engine_kwargs(url: str) -> dict:
+    if url.startswith("sqlite"):
+        # One file, many threads (scheduler + bot + requests).
+        return {"connect_args": {"check_same_thread": False}}
+    return {"pool_pre_ping": True, "pool_size": 5, "max_overflow": 10}
+
+
+engine = create_engine(env_settings().database_url, **_engine_kwargs(env_settings().database_url))
+SessionLocal = sessionmaker(bind=engine, autoflush=False, expire_on_commit=False)
+
+
+def init_db() -> None:
+    """Create any missing tables. The schema is additive, so this is enough."""
+    from app import models  # noqa: F401  (register the mappers)
+
+    Base.metadata.create_all(bind=engine)
+
+
+@contextmanager
+def session_scope() -> Iterator[Session]:
+    """A transactional session for background jobs and scripts."""
+    session = SessionLocal()
+    try:
+        yield session
+        session.commit()
+    except Exception:
+        session.rollback()
+        raise
+    finally:
+        session.close()
+
+
+def get_session() -> Iterator[Session]:
+    """FastAPI dependency: one session per request, committed by the endpoint."""
+    session = SessionLocal()
+    try:
+        yield session
+    finally:
+        session.close()