template tutoring-admin-dashboard v1

backend/app/db.py

@@ -0,0 +1,67 @@
+"""Database engine + session.
+
+Reads DATABASE_URL from the environment (provisioned Postgres). The engine is
+created with a short connect timeout and a probe: if Postgres is unreachable at
+startup, we fall back to a local SQLite file so the app still runs (Preview,
+offline dev). The rest of the app never chooses a database — it imports
+``SessionLocal`` and ``engine`` from here.
+"""
+
+from __future__ import annotations
+
+import os
+from collections.abc import Generator
+
+from sqlalchemy import create_engine, text
+from sqlalchemy.orm import DeclarativeBase, Session, sessionmaker
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+def _normalize(url: str) -> str:
+    # SQLAlchemy + psycopg3 wants the postgresql+psycopg driver.
+    if url.startswith("postgresql://"):
+        return url.replace("postgresql://", "postgresql+psycopg://", 1)
+    if url.startswith("postgres://"):
+        return url.replace("postgres://", "postgresql+psycopg://", 1)
+    return url
+
+
+def _make_engine():
+    url = os.getenv("DATABASE_URL", "").strip()
+    if url:
+        pg_url = _normalize(url)
+        try:
+            eng = create_engine(
+                pg_url,
+                pool_pre_ping=True,
+                connect_args={"connect_timeout": 5},
+            )
+            with eng.connect() as conn:
+                conn.execute(text("SELECT 1"))
+            print("[db] using Postgres")
+            return eng
+        except Exception as exc:  # noqa: BLE001
+            print(f"[db] Postgres unreachable ({exc}); falling back to SQLite")
+
+    sqlite_path = os.path.join(os.path.dirname(__file__), "..", "app_fallback.db")
+    eng = create_engine(
+        f"sqlite:///{os.path.abspath(sqlite_path)}",
+        connect_args={"check_same_thread": False},
+    )
+    print("[db] using SQLite fallback")
+    return eng
+
+
+engine = _make_engine()
+SessionLocal = sessionmaker(bind=engine, autoflush=False, autocommit=False)
+
+
+def get_db() -> Generator[Session, None, None]:
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()