Trade-offs in AWS DynamoDB

brew tap tensor9ine/tensor9
brew install tensor9
tensor9 --version

tensor9 explain \
  -origin aws::1.0.0::dynamodb::table \
  -target google::1.0.0::cloudsql::postgresql \
  -operation TransactWriteItems \
  -fmt Human

export AWS_ENDPOINT_URL_DYNAMODB="<installed Cloud SQL-backed DynamoDB test endpoint>"
export AWS_PROFILE="<origin test credential profile>"
export AWS_REGION="<origin region accepted by the endpoint>"

aws dynamodb list-tables --limit 1 --no-paginate

import os
import uuid
from decimal import Decimal

import boto3
from botocore.exceptions import ClientError

dynamodb = boto3.client(
    "dynamodb",
    endpoint_url="<installed Cloud SQL-backed DynamoDB test endpoint>",
    region_name=os.environ["AWS_REGION"],
)
table = "tradeoffs-orders"
print("Disposable table:", table, flush=True)
dynamodb.create_table(
    TableName=table,
    AttributeDefinitions=[{"AttributeName": "id", "AttributeType": "S"}],
    KeySchema=[{"AttributeName": "id", "KeyType": "HASH"}],
    BillingMode="PAY_PER_REQUEST",
    StreamSpecification={"StreamEnabled": False},
)
dynamodb.get_waiter("table_exists").wait(TableName=table)
amount = "12345678901234567890.12"
dynamodb.put_item(TableName=table, Item={
    "id": {"S": "order-1"}, "status": {"S": "pending"},
    "amount": {"N": amount},
})
dynamodb.put_item(TableName=table, Item={
    "id": {"S": "stock-1"}, "quantity": {"N": "1"},
})

def read_state():
    def read(key):
        return dynamodb.get_item(
            TableName=table, Key={"id": {"S": key}},
            ConsistentRead=True,
        )["Item"]
    order, stock = read("order-1"), read("stock-1")
    assert Decimal(order["amount"]["N"]) == Decimal(amount)
    return order["status"]["S"], Decimal(stock["quantity"]["N"])

def transaction(expected_status):
    return [
        {"Update": {
            "TableName": table, "Key": {"id": {"S": "order-1"}},
            "UpdateExpression": "SET #s = :paid",
            "ConditionExpression": "#s = :expected",
            "ExpressionAttributeNames": {"#s": "status"},
            "ExpressionAttributeValues": {
                ":paid": {"S": "paid"},
                ":expected": {"S": expected_status},
            },
        }},
        {"Update": {
            "TableName": table, "Key": {"id": {"S": "stock-1"}},
            "UpdateExpression": "SET #q = #q - :one",
            "ConditionExpression": "#q >= :one",
            "ExpressionAttributeNames": {"#q": "quantity"},
            "ExpressionAttributeValues": {":one": {"N": "1"}},
        }},
    ]

try:
    dynamodb.transact_write_items(
        TransactItems=transaction("not-the-current-status"),
        ClientRequestToken=str(uuid.uuid4()),
    )
except ClientError as error:
    if error.response["Error"]["Code"] != "TransactionCanceledException":
        raise
else:
    raise AssertionError("The false condition was accepted")
assert read_state() == ("pending", Decimal("1"))

request = {
    "TransactItems": transaction("pending"),
    "ClientRequestToken": str(uuid.uuid4()),
}
dynamodb.transact_write_items(**request)
assert read_state() == ("paid", Decimal("0"))
dynamodb.transact_write_items(**request)
assert read_state() == ("paid", Decimal("0"))
print("Checks passed; inspect and clean up:", table)

aws dynamodb describe-table --table-name tradeoffs-orders
aws dynamodb delete-table --table-name tradeoffs-orders
aws dynamodb wait table-not-exists --table-name tradeoffs-orders