Is there any way to make sure no duplicate items get added in firestore, I'm using Flutter and Firebase and I'm pretty new to this

Question

   Future addCart() async{
     final FirebaseAuth _auth = FirebaseAuth.instance;
     var currentUser = _auth.currentUser;
     CollectionReference _collectionRef = FirebaseFirestore.instance.collection("users-cart- 
     items");
    return _collectionRef.doc(currentUser!.email).collection("items").doc().set(
      {
       "name": widget.name,
        "price": widget.price,
        "images": widget.image,
      }).then((value) => print("Added To Cart"));

     }

I'm using collectionReference and it does not have any .contain method to check if there are items of the same type already existing.