DynamoDB Streamからのイベントをunmarshallを使って整形する(TypeScript)

DynamoDB Streamからlambdaへ送られてくるデータは以下の形で送られてくる

{
  ApproximateCreationDateTime: 1644309749,
  Keys: {
    meta: {
      S: "Sample:1:1"
    },
    id: {
      S: "Sample:1:1:621d1946-c5d6-4187-872d-a766856331a5"
    }
  },
  NewImage: {
    product: {
      S: "テストビール"
    },
    meta: {
      S: "Sample:1:1"
    },
    sampleArray: {
      L: [
        {
          N: "1"
        },
        {
          N: "11"
        },
        {
          N: "12"
        },
        {
          N: "34"
        }
      ]
    },
    id: {
      S: "Sample:1:1:621d1946-c5d6-4187-872d-a766856331a5"
    },
    ttl: {
      N: "1675845748"
    },
    sampleRate: {
      N: "12.34"
    },
    timestamp: {
      N: "1639560046429"
    },
    sampleBool: {
      BOOL: true
    }
  },
  OldImage: {
    product: {
      S: "テストビール"
    },
    meta: {
      S: "Sample:1:1"
    },
    sampleArray: {
      L: [
        {
          N: "1"
        },
        {
          N: "11"
        },
        {
          N: "12"
        },
        {
          N: "34"
        }
      ]
    },
    id: {
      S: "Sample:1:1:621d1946-c5d6-4187-872d-a766856331a5"
    },
    ttl: {
      N: "1675845748"
    },
    sampleRate: {
      N: "12.34"
    },
    timestamp: {
      N: "1639560046429"
    }
  },
  SequenceNumber: "200000000012909188526",
  SizeBytes: 336,
  StreamViewType: "NEW_IMAGE"
};

SDKのライブラリであるDynamoDBDocumentClientを使用したい場合

id: { S: "Sample:1:1:621d1946-c5d6-4187-872d-a766856331a5" }

を

id: "Sample:1:1:621d1946-c5d6-4187-872d-a766856331a5"

のように変換したい

そうした時、「unmarshall」というライブラリを使用することで変換することができます

以下コードサンプル

import * as AWSLambda from "aws-lambda";
import * as AWS from "aws-sdk";

interface UnmarshallAttributeValue {
  [key: string]: string | string[] | number | number[] | boolean | UnmarshallAttributeValue;
}

interface UnmarshallStreamRecord {
  ApproximateCreationDateTime?: number;
  Keys?: UnmarshallAttributeValue;
  NewImage?: UnmarshallAttributeValue;
  OldImage?: UnmarshallAttributeValue;
  SequenceNumber?: string;
  SizeBytes?: number;
  StreamViewType?: "KEYS_ONLY" | "NEW_IMAGE" | "OLD_IMAGE" | "NEW_AND_OLD_IMAGES";
}

const unmarshall = AWS.DynamoDB.Converter.unmarshall;

export class DynamoDBStream {

  static generateEventPayload(
    data: AWSLambda.StreamRecord
  ) {
    const unmarshalled: UnmarshallStreamRecord = {};
    if (data) {
      if (data.ApproximateCreationDateTime) { unmarshalled.ApproximateCreationDateTime = data.ApproximateCreationDateTime; }
      if (data.SequenceNumber) { unmarshalled.SequenceNumber = data.SequenceNumber; }
      if (data.SizeBytes) { unmarshalled.SizeBytes = data.SizeBytes; }
      if (data.StreamViewType) { unmarshalled.StreamViewType = data.StreamViewType; }
      if (data.Keys) { unmarshalled.Keys = unmarshall(data.Keys); }
      if (data.NewImage) { unmarshalled.NewImage = unmarshall(data.NewImage); }
      if (data.OldImage) { unmarshalled.OldImage = unmarshall(data.OldImage); }
    }
    return unmarshalled;
  }

テストコード(jest)

describe("generateEventPayload", () => {
  test("generateEventPayload", () => {
    const input = {
      ApproximateCreationDateTime: 1644309749,
      Keys: {
        meta: {
          S: "Sample:1:1"
        },
        id: {
          S: "Sample:1:1:621d1946-c5d6-4187-872d-a766856331a5"
        }
      },
      NewImage: {
        product: {
          S: "テストビール"
        },
        contents: {
          N: "300"
        },
        meta: {
          S: "Sample:1:1"
        },
        sampleArray: {
          L: [
            {
              N: "1"
            },
            {
              N: "11"
            },
            {
              N: "12"
            },
            {
              N: "34"
            }
          ]
        },
        lotId: {
          S: "2306"
        },
        id: {
          S: "Sample:1:1:621d1946-c5d6-4187-872d-a766856331a5"
        },
        ttl: {
          N: "1675845748"
        },
        Sample: {
          N: "12.34"
        },
        timestamp: {
          N: "1639560046429"
        },
        sampleBool: {
          BOOL: true
        }
      },
      OldImage: {
        product: {
          S: "テストビール"
        },
        contents: {
          N: "300"
        },
        meta: {
          S: "Sample:1:1"
        },
        sampleArray: {
          L: [
            {
              N: "1"
            },
            {
              N: "11"
            },
            {
              N: "12"
            },
            {
              N: "34"
            }
          ]
        },
        lotId: {
          S: "2306"
        },
        id: {
          S: "Sample:1:1:621d1946-c5d6-4187-872d-a766856331a5"
        },
        ttl: {
          N: "1675845748"
        },
        Sample: {
          N: "12.34"
        },
        timestamp: {
          N: "1639560046429"
        }
      },
      SequenceNumber: "200000000012909188526",
      SizeBytes: 336,
      StreamViewType: "NEW_IMAGE" as "NEW_IMAGE"
    };
    const expected = {
      ApproximateCreationDateTime: 1644309749,
      Keys: {
        meta: "Sample:1:1",
        id: "Sample:1:1:621d1946-c5d6-4187-872d-a766856331a5"
      },
      NewImage: {
        product: "テストビール",
        contents: 300,
        meta: "Sample:1:1",
        sampleArray: [1, 11, 12, 34],
        lotId: "2306",
        id: "Sample:1:1:621d1946-c5d6-4187-872d-a766856331a5",
        ttl: 1675845748,
        Sample: 12.34,
        timestamp: 1639560046429,
        sampleBool: true
      },
      OldImage: {
        product: "テストビール",
        contents: 300,
        meta: "Sample:1:1",
        sampleArray: [1, 11, 12, 34],
        lotId: "2306",
        id: "Sample:1:1:621d1946-c5d6-4187-872d-a766856331a5",
        ttl: 1675845748,
        Sample: 12.34,
        timestamp: 1639560046429
      },
      SequenceNumber: "200000000012909188526",
      SizeBytes: 336,
      StreamViewType: "NEW_IMAGE"
    };

    expect(DynamoDBStream.generateEventPayload(input)).toEqual(expected);
  });
});