Amazon DynamoDB Conditional Update of an Existing Item

arazzo: 1.0.1
info:
  title: Amazon DynamoDB Conditional Update of an Existing Item
  summary: Read an item, then update it only when it already exists.
  description: >-
    A read-modify-write pattern that guards against creating phantom items.
    The workflow first reads the target item with GetItem; when the item
    exists it applies an UpdateItem with an update expression, and when the
    item is absent it stops without writing. Every step spells out its
    request inline, including the AWS JSON protocol X-Amz-Target header, so
    the flow can be read and executed without opening the underlying
    OpenAPI description.
  version: 1.0.0
sourceDescriptions:
- name: dynamodbApi
  url: ../openapi/amazon-dynamodb-openapi.yml
  type: openapi
workflows:
- workflowId: conditional-update-item
  summary: Update an item only when a prior read confirms it exists.
  description: >-
    Reads an item by primary key and branches: when the item is present it
    runs UpdateItem, otherwise it ends without modifying anything.
  inputs:
    type: object
    required:
    - tableName
    - key
    - updateExpression
    properties:
      tableName:
        type: string
        description: The name of the table containing the item.
      key:
        type: object
        description: The primary key of the item, as a map of attribute name to AttributeValue.
      updateExpression:
        type: string
        description: The update expression to apply (e.g. "SET #s = :s").
      expressionAttributeNames:
        type: object
        description: Optional substitution tokens for attribute names.
      expressionAttributeValues:
        type: object
        description: Values substituted into the update expression.
  steps:
  - stepId: readItem
    description: Read the target item by its primary key to confirm it exists.
    operationId: getItem
    parameters:
    - name: X-Amz-Target
      in: header
      value: DynamoDB_20120810.GetItem
    requestBody:
      contentType: application/x-amz-json-1.0
      payload:
        TableName: $inputs.tableName
        Key: $inputs.key
        ConsistentRead: true
    successCriteria:
    - condition: $statusCode == 200
    outputs:
      item: $response.body#/Item
    onSuccess:
    - name: itemExists
      type: goto
      stepId: updateItem
      criteria:
      - context: $response.body
        condition: $.Item != null
        type: jsonpath
    - name: itemMissing
      type: end
      criteria:
      - context: $response.body
        condition: $.Item == null
        type: jsonpath
  - stepId: updateItem
    description: >-
      Apply the update expression to the item that the prior read confirmed
      exists, returning the new attribute values.
    operationId: updateItem
    parameters:
    - name: X-Amz-Target
      in: header
      value: DynamoDB_20120810.UpdateItem
    requestBody:
      contentType: application/x-amz-json-1.0
      payload:
        TableName: $inputs.tableName
        Key: $inputs.key
        UpdateExpression: $inputs.updateExpression
        ExpressionAttributeNames: $inputs.expressionAttributeNames
        ExpressionAttributeValues: $inputs.expressionAttributeValues
        ReturnValues: ALL_NEW
    successCriteria:
    - condition: $statusCode == 200
    outputs:
      attributes: $response.body#/Attributes
  outputs:
    updatedAttributes: $steps.updateItem.outputs.attributes