Firebase：如何删除一个集合中的集合？

Question

I am developing a cart page in Flutter. For deleting a particular item in the cart, I am facing an issue. I want to delete a document inside collection "items" which is inside collection "myOrders"

myOrders => docID => items => docID(to be deleted)

This is the code I tried,

    Future deleteData(BuildContext context)
    {
      final user = Provider.of<Userr?>(context,listen: false);
      CollectionReference _collectionRef = FirebaseFirestore.instance.collection('myOrders');
      return _collectionRef.doc(user?.uid).collection('items').doc().delete();
    }

I need to know why it is not getting deleted and what change I need to do in the code!

Answer 1

You have to pass the id of the document to be deleted. so modify your code as

Future deleteData(BuildContext context)
{
  final user = Provider.of<Userr?>(context,listen: false);
  CollectionReference _collectionRef = FirebaseFirestore.instance.collection('myOrders');
  return _collectionRef.doc(user?.uid).collection('items').doc('document_id_to_be_deleted').delete();
}

Answer 2

Each time you're calling .doc() to create the following reference, without passing anything as an argument:

 _collectionRef.doc(user?.uid).collection('items').doc()
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It literally means that you're always generating a new unique document ID. When you call delete() , you're trying to delete a document that actually doesn't exist, hence that behavior.

If you want to create a reference that points to a particular item (document) inside the items sub-collection, then you have to pass the document ID of that item, which already exists in the database, and not generate a brand new one. So to solve this, get the document ID of the item you want to delete and pass it to the .doc() function like this:

 _collectionRef.doc(user?.uid).collection('items').doc('itemDocId')
//                                                         👆