How to get eventName in AWS Lambda Function?

Question

I am very new to AWS Lambda. I have a trigger setup between my Lambda func and a DynamoDB table when my table is modified. The Lambda function successfully prints the event to cloud watch logs. I am having trouble figuring out how to check if the event is an INSERT or MODIFY in dynamoDB. I want to check with an if statement. When I just print(event) I get

{
  "Records": [
    {
      "eventID": "26e6ac4f1c16fc40fd91536430c1ac72",
      "eventName": "MODIFY",
      "eventVersion": "1.1",
      "eventSource": "aws:dynamodb",
      "awsRegion": "us-east-1",
      "dynamodb": {
        "ApproximateCreationDateTime": 1612293148,
        "Keys": {
          "id": {
            "S": "d66ec59b-b807-4db9-96ed-3ebd3638779a450b7a75-6dce-4be9-babf-1077adb84b02"
          }
        },
        "NewImage": {
          "__typename": {
            "S": "Conversation"
          },
          "members": {
            "L": [
              {
                "S": "450b7a75-6dce-4be9-babf-1077adb84b02"
              },
              {
                "S": "d66ec59b-b807-4db9-96ed-3ebd3638779a"
              }
            ]
          },
          "isRead": {
            "BOOL": false
          },
          "recipient": {
            "S": "d66ec59b-b807-4db9-96ed-3ebd3638779a"
          },
          "latestMessage": {
            "S": "Hey man"
          },
          "id": {
            "S": "d66ec59b-b807-4db9-96ed-3ebd3638779a450b7a75-6dce-4be9-babf-1077adb84b02"
          },
          "latestMessageSenderSub": {
            "S": "450b7a75-6dce-4be9-babf-1077adb84b02"
          },
          "updatedAt": {
            "S": "02/02/2021 - 14:12:27"
          }
        },
        "OldImage": {
          "__typename": {
            "S": "Conversation"
          },
          "members": {
            "L": [
              {
                "S": "450b7a75-6dce-4be9-babf-1077adb84b02"
              },
              {
                "S": "d66ec59b-b807-4db9-96ed-3ebd3638779a"
              }
            ]
          },
          "isRead": {
            "BOOL": false
          },
          "recipient": {
            "S": "d66ec59b-b807-4db9-96ed-3ebd3638779a"
          },
          "latestMessage": {
            "S": "Yooooo"
          },
          "id": {
            "S": "d66ec59b-b807-4db9-96ed-3ebd3638779a450b7a75-6dce-4be9-babf-1077adb84b02"
          },
          "latestMessageSenderSub": {
            "S": "450b7a75-6dce-4be9-babf-1077adb84b02"
          },
          "updatedAt": {
            "S": "02/02/2021 - 12:40:09"
          }
        },
        "SequenceNumber": "47015900000000007518411700",
        "SizeBytes": 753,
        "StreamViewType": "NEW_AND_OLD_IMAGES"
      },
      "eventSourceARN": "arn:aws:dynamodb:us-east-1:69639064567851005:table/Conversation-jklhofiuhvouerhoh-dev/stream/2021-01-23T21:25:34.783"
    }
  ]
}

But with my if statements added to my lambda func I get the following error

[ERROR] KeyError: 'eventName'Traceback (most recent call last): File "/var/task/lambda_function.py", line 6, in lambda_handler if event['eventName'] == 'MODIFY':

Lambda Function:

import json

def lambda_handler(event, context):
    # TODO implement
    print(event)
    if event['eventName'] == 'MODIFY':
        #Run some code
        print('MODIFY')
    elif event['eventName'] == 'INSERT':
        #Run some code
        print('INSERT')
    return {
        'statusCode': 200,
        'body': json.dumps('Hello from Lambda!')
    }

How can I get the eventName?

zyd · Accepted Answer · 2021-02-02 19:33:34Z

5

The events you're receiving in your Lambda function are listed as an array under the 'Records' key. So to find the event name you'll need to do something like this:

for e in event['Records']:
    if e['eventName'] == 'MODIFY':
        print('MODIFY')
    elif e['eventName'] == 'INSERT':
        #Run some code
        print('INSERT')
    return {
        'statusCode': 200,
        'body': json.dumps('Hello from Lambda!')
    }

answered Feb 2, 2021 at 19:33

zyd

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3 Comments

jarmod Over a year ago

Bonus point for iterating over the event records. Many people simply assume there will be one, and only one, event and they only process event['Records'][0] and then wonder why some events are not being processed.

GBMR Over a year ago

This solution worked! How do I get the table keys as well such as the id?

zyd Over a year ago

@GBMR - list(e['dynamodb']['Keys'].keys()) should get all the keys I think. If you want the key values too then just e['dynamodb']['Keys']

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