DynamoDBのSet型でデータの数が0個になったとき、Attribute自体が残るか消えるか確認してみた

aws dynamodb create-table \
    --table-name set-test-table \
    --attribute-definitions AttributeName=itemId,AttributeType=S \
    --key-schema AttributeName=itemId,KeyType=HASH \
    --billing-mode PAY_PER_REQUEST

import boto3

table = boto3.resource("dynamodb").Table("set-test-table")

def main() -> None:
    put(
        {
            "itemId": "item1",
            "tags": {
                "Apple",
                "Banana",
            },
        }
    )

    add("item1", {"Cherry", "Durian"})

def put(item: dict) -> None:
    table.put_item(Item=item)

def add(item_id: str, tags: set[str]) -> None:
    table.update_item(
        Key={"itemId": item_id},
        UpdateExpression="ADD #tags :tags",
        ExpressionAttributeNames={"#tags": "tags"},
        ExpressionAttributeValues={":tags": tags},
    )

if __name__ == "__main__":
    main()

import boto3

table = boto3.resource("dynamodb").Table("set-test-table")

def main() -> None:
    delete("item1", {"Apple", "Banana", "Cherry", "Durian"})

def delete(item_id: str, tags: set[str]) -> None:
    table.update_item(
        Key={"itemId": item_id},
        UpdateExpression="DELETE #tags :tags",
        ExpressionAttributeNames={"#tags": "tags"},
        ExpressionAttributeValues={":tags": tags},
    )

if __name__ == "__main__":
    main()