(aws-stepfunctions-tasks): DynamoAttributeValue.fromNumber() breaks when passed a JsonPath

DynamoAttributeValue.fromNumber() synths incorrectly when passed a JsonPath.numberAt() for getting a number from a step’s input.

Example:

DynamoAttributeValue.fromNumber(JsonPath.numberAt('$.viewCount')

Synths as:

{\":viewCount\":{\"N\":\"-1.888154589708819e+289\"}}

Reproduction Steps

1. Deploy ProblemStack

import { Table, AttributeType, BillingMode } from '@aws-cdk/aws-dynamodb';
import { LogGroup, RetentionDays } from '@aws-cdk/aws-logs';
import { StateMachine, Chain, StateMachineType, LogLevel, JsonPath } from '@aws-cdk/aws-stepfunctions';
import { DynamoUpdateItem, DynamoAttributeValue, DynamoReturnValues } from '@aws-cdk/aws-stepfunctions-tasks';
import { Stack, Construct, StackProps, RemovalPolicy } from '@aws-cdk/core';


export class ProblemStack extends Stack {

  constructor(scope: Construct, id: string, props: StackProps = {}) {
    super(scope, id, props);

    const table = new Table(this, 'MyTable', {
      partitionKey: { name: 'id', type: AttributeType.STRING },
      billingMode: BillingMode.PAY_PER_REQUEST,
      removalPolicy: RemovalPolicy.DESTROY,
    });

    const updateViewCount = new DynamoUpdateItem(this, 'PutVideosViewCount', {
      table: table,
      key: {
        id: DynamoAttributeValue.fromString(JsonPath.stringAt('$.id')),
      },
      returnValues: DynamoReturnValues.ALL_NEW,
      updateExpression: 'SET viewCount = :viewCount',
      expressionAttributeValues: {
        ':viewCount': DynamoAttributeValue.fromNumber(JsonPath.numberAt('$.viewCount')),
      },
    });

    const main = Chain.start(updateViewCount);

    const stateMachineLogs = new LogGroup(this, 'MyStateMachineLogGroup', {
      retention: RetentionDays.THREE_MONTHS,
    });

    new StateMachine(this, 'MyStateMachine', {
      definition: main,
      stateMachineType: StateMachineType.STANDARD,
      tracingEnabled: true,
      logs: {
        destination: stateMachineLogs,
        includeExecutionData: true,
        level: LogLevel.ALL,
      },
    });
  }
}

2. Insert a record into the DynamoDB table

{
    "id": "foo",
    "viewCount": 10
}

3. Start state machine execution with event

{
    "id": "foo",
    "viewCount": 1234
}

What did you expect to happen?

The template should synth to extract the number from the input and then update the record in the db.

What actually happened?

The execution fails with the error:

"ExpressionAttributeValues contains invalid value: Number overflow. Attempting to store a number with magnitude larger than supported range for key :viewCount (Service: AmazonDynamoDBv2; Status Code: 400; Error Code: ValidationException; Request ID: c056d945-3aa5-484e-8c64-eb75b9b9041c; Proxy: null)

This is because the template was synthed as:

\"ExpressionAttributeValues\":{\":viewCount\":{\"N\":\"-1.888154589708819e+289\"}}

Environment

• CDK CLI Version : 1.83.0
• Framework Version:
• Node.js Version: v12.19.0
• OS : Linux
• Language (Version): TypeScript Version 4.0.5

Other

---

This is 🐛 Bug Report

[lodi-g]

Quite ugly workaround, but it works and does not require one to change the functions themselves, only the CDK code.

function dynamoNumberFromJson(jsonPath: string) {
  return tasks.DynamoAttributeValue.numberFromString(
    sfn.JsonPath.stringAt(`States.Format('{}', ${jsonPath})`)
  );
}

Using States.Format, it’ll “convert” the number to a string. Not happy with it but it works.

[GhostzLab]

@shivlaks Thank you for your help

When I change it to use numberFromString and stringAt. The execution still fails but with a different error:

"An error occurred while executing the state 'PutVideosViewCount' (entered at the event id #2). The Parameters '{\"Key\":{\"id\":{\"S\":\"foo\"}},\"TableName\":\"ProblemStack-MyTable794EDED1-1NWAFVLUWWLV7\",\"ExpressionAttributeValues\":{\":viewCount\":{\"N\":1234}},\"ReturnValues\":\"ALL_NEW\",\"UpdateExpression\":\"SET viewCount = :viewCount\"}' could not be used to start the Task: [The value for the field 'N' must be a STRING]"

The TaskStateEntered for the state is the following. As you can see, viewCount is a number.

{
  "name": "PutVideosViewCount",
  "input": {
    "id": "foo",
    "viewCount": 1234
  },
  "inputDetails": {
    "truncated": false
  }
}

I believe this is because the template was synthed as follows, so it’s not representing value of N.$ as a string.:

\"ExpressionAttributeValues\":{\":viewCount\":{\"N.$\":\"$.viewCount\"}}