working with login and building inventory

trade-hub/backend/app/db.py

@@ -0,0 +1,89 @@
+"""Database engine, session factory and schema bootstrap.
+
+The engine is created lazily so importing the app (and loading the read-only
+catalog) never requires a reachable database.
+"""
+import logging
+import time
+
+from sqlalchemy import create_engine, text
+from sqlalchemy.exc import IntegrityError, OperationalError, ProgrammingError
+from sqlalchemy.orm import sessionmaker
+from sqlalchemy.pool import StaticPool
+
+from app import config
+from app.models import Base
+
+log = logging.getLogger(__name__)
+
+_engine = None
+_session_factory = None
+
+
+def get_engine():
+    """Return the process-wide engine, creating it on first use."""
+    global _engine, _session_factory
+    if _engine is None:
+        url = config.DATABASE_URL
+        kwargs = {"pool_pre_ping": True, "future": True}
+        if url.startswith("sqlite"):
+            kwargs["connect_args"] = {"check_same_thread": False}
+            if ":memory:" in url or url in {"sqlite://", "sqlite+pysqlite://"}:
+                kwargs["poolclass"] = StaticPool
+        _engine = create_engine(url, **kwargs)
+        _session_factory = sessionmaker(
+            bind=_engine, autoflush=False, autocommit=False, expire_on_commit=False
+        )
+    return _engine
+
+
+def get_session_factory():
+    get_engine()
+    return _session_factory
+
+
+def get_db():
+    """FastAPI dependency yielding a request-scoped SQLAlchemy session."""
+    db = get_session_factory()()
+    try:
+        yield db
+    finally:
+        db.close()
+
+
+def init_db(wait_seconds: int = 0, interval: float = 1.0) -> None:
+    """Create missing tables, retrying while PostgreSQL finishes booting.
+
+    `create_all(checkfirst=True)` is idempotent and safe to run on every start.
+    It does not migrate changed columns; introduce Alembic when the schema
+    starts evolving in place.
+    """
+    deadline = time.monotonic() + max(wait_seconds, 0)
+    while True:
+        try:
+            engine = get_engine()
+            with engine.connect() as conn:
+                conn.execute(text("SELECT 1"))
+            Base.metadata.create_all(bind=engine, checkfirst=True)
+            return
+        except (OperationalError, IntegrityError, ProgrammingError) as exc:
+            # A concurrent startup may have created the tables first.
+            if "already exists" in str(exc).lower():
+                return
+            if time.monotonic() >= deadline:
+                raise
+            log.warning(
+                "database not ready (%s); retrying in %.1fs",
+                exc.__class__.__name__,
+                interval,
+            )
+            time.sleep(interval)
+
+
+def db_healthy() -> bool:
+    try:
+        with get_engine().connect() as conn:
+            conn.execute(text("SELECT 1"))
+        return True
+    except Exception:
+        return False