DynamoDBのSet型で、新しいAttributeに対するaddをした場合にどうなるのか試してみた

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": "item777"})

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

if __name__ == "__main__":
    main()

import boto3

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

def main() -> None:
    update("item777", {"apple", "banana"})
    update("item777", {"cherry", "durian"})

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

if __name__ == "__main__":
    main()