feature: Das Anlegen doppelter Einträge muss mit der richtigen Fehlermeldung abgelehnt werden

Es darf kein Serverfehlersein.

api/main.py

@@ -1,11 +1,13 @@
 import datetime
 
 from fastapi import FastAPI
-from sqlalchemy.exc import IntegrityError
+from fastapi.encoders import jsonable_encoder
+from sqlalchemy.exc import IntegrityError, DataError
 from sqlmodel import Session, SQLModel, create_engine, select
 from contextlib import asynccontextmanager
 from api.models import Car, FuelItem
 from pydantic_settings import BaseSettings, SettingsConfigDict
+from fastapi.responses import JSONResponse
 
 
 class Settings(BaseSettings):
@@ -46,8 +48,9 @@ def fill_database():
         session.refresh(fill_item)
 
 
+# noinspection PyUnusedLocal
 @asynccontextmanager
-async def lifespan(app: FastAPI):
+async def lifespan(actual_app: FastAPI):
     # startup
     create_db_and_tables()
     try:
@@ -60,13 +63,21 @@ async def lifespan(app: FastAPI):
 app = FastAPI(lifespan=lifespan)
 
 
+def save_object(obj):
+    with Session(engine) as session:
+        try:
+            session.add(obj)
+            session.commit()
+            session.refresh(obj)
+            return obj
+        except IntegrityError|DataError as e:
+            content = jsonable_encoder({"message": e})
+            return JSONResponse(content=content, status_code=400)
+
+
 @app.post("/cars/")
 def create_cars(car: Car):
-    with Session(engine) as session:
-        session.add(car)
-        session.commit()
-        session.refresh(car)
-        return car
+    return save_object(car)
 
 
 @app.get("/cars/")
@@ -78,11 +89,7 @@ def read_cars():
 
 @app.post("/fill_items/")
 def create_cars(fill_item: FuelItem):
-    with Session(engine) as session:
-        session.add(fill_item)
-        session.commit()
-        session.refresh(fill_item)
-        return fill_item
+    return save_object(fill_item)
 
 
 @app.get("/fill_items/")