Constructing a linked list

Users GraphQL
2

You can to control the mutation depending on the size of the list using variables.
It can be achieved in the following way.
Get the list(Assume ListID is 0x0123)

query {
	getList(id: "0x123") {
		head
		tail
	}
}

After getting the head and tail pointer you can decide if the list is empty.
Empty condition: head = null and tail = null

mutation updateList($patch: UpdateListInput!) {
	updateList(input: $patch) {
		list {
			listID
			head
			tail
		}
	}
}

When the list is empty, $patch

{
	"patch": {
		"filter": {
			"listID": ["0x123"]
		},
		"set": {
			"head": "0x01",
			"tail": "0x01"
		}
	}
}

Update the tail after adding to the List.

{
	"patch": {
		"filter": {
			"listID": ["0x123"]
		},
		"set": {
			"tail": "0x02"
		}
	}
}

Update the head after deletion from the List.

{
	"patch": {
		"filter": {
			"listID": ["0x123"]
		},
		"set": {
			"head": "0x02"
		}
	}
}