🚧 WIP

backend/app/db.py

@@ -0,0 +1,53 @@
+"""SQLAlchemy engine/session plumbing and ORM base class."""
+
+from __future__ import annotations
+
+from collections.abc import Generator
+
+from sqlalchemy import create_engine
+from sqlalchemy.orm import DeclarativeBase, Session, sessionmaker
+
+from app.config import get_settings
+
+_engine = None
+_SessionFactory: sessionmaker[Session] | None = None
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+def _url_with_driver() -> str:
+    url = get_settings().database_url
+    # Accept plain postgresql:// URLs by normalising to the psycopg driver.
+    if url.startswith("postgresql://"):
+        url = url.replace("postgresql://", "postgresql+psycopg://", 1)
+    return url
+
+
+def get_engine():
+    global _engine
+    if _engine is None:
+        _engine = create_engine(_url_with_driver(), pool_pre_ping=True, future=True)
+    return _engine
+
+
+def get_session_factory() -> sessionmaker[Session]:
+    global _SessionFactory
+    if _SessionFactory is None:
+        _SessionFactory = sessionmaker(bind=get_engine(), future=True)
+    return _SessionFactory
+
+
+def get_db() -> Generator[Session, None, None]:
+    """FastAPI dependency yielding a database session per request."""
+    factory = get_session_factory()
+    session = factory()
+    try:
+        yield session
+        session.commit()
+    except Exception:
+        session.rollback()
+        raise
+    finally:
+        session.close()