Demo Server, Fix Timescale (#12746)

- improve demo server
- missing deps

libs/cli/langchain_cli/dev_scripts.py

@@ -3,7 +3,8 @@
 """
 
 from fastapi import FastAPI
-from langserve.packages import add_package_route
+from langserve import add_routes
+from langserve.packages import get_langserve_export
 
 from langchain_cli.utils.packages import get_package_root
 
@@ -14,5 +15,17 @@ def create_demo_server():
     """
     app = FastAPI()
     package_root = get_package_root()
-    add_package_route(app, package_root, "")
+    pyproject = package_root / "pyproject.toml"
+    try:
+        package = get_langserve_export(pyproject)
+
+        mod = __import__(package["module"], fromlist=[package["attr"]])
+
+        chain = getattr(mod, package["attr"])
+        add_routes(app, chain)
+    except KeyError as e:
+        raise KeyError("Missing fields from pyproject.toml") from e
+    except ImportError as e:
+        raise ImportError("Could not import module defined in pyproject.toml") from e
+
     return app