add fastapi init

chat/db/session.py

@@ -0,0 +1,13 @@
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+from config import SQLALCHEMY_DATABASE_URL
+
+engine = create_engine(SQLALCHEMY_DATABASE_URL, pool_pre_ping=True)
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+
+def get_db():
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()