Attribute in DynamoDB cannot be updated by lambda function

Question

Hello,

I was following the serverless workshop examples, but running into a problem!
My lambda handler![here](/media/postImages/original/IM13YY7JLdSPqaM9gAPRSTAA) can't update the attribute 'status' shown in the ![schema](/media/postImages/original/IMoJlnQtpERrC8OPh05poIOw).

The error message is a ValidationException complaining about the document path ![log here](/media/postImages/original/IMZJyulHI0QCGN1gDrvjrYOQ).

How should I troubleshoot this further? Has someone had this problem before?

Thanks a lot!

Here's the lambda handler code:

```
import json
import os
import boto3

from decimal import Decimal

ORDERS_TABLE = os.environ['ORDERS_TABLE_NAME']
dynamodb = boto3.resource('dynamodb')
ddbTable = dynamodb.Table(ORDERS_TABLE)

def lambda_handler(event, context):
    response = None
    print(str(event))
    try:

status_code = 200
        
        order_data = event['detail']['data']
        
        status = order_data['status']
        orderId = order_data['orderId']
        userId = order_data['userId']

key={ 
        "userId": userId,
        "orderId": orderId}

update_expression = "SET #data.#status = :status"
        expression_attribute_values = {":status": status} 
        expression_attribute_names = {"#data": "data", "#status": "status"}
        print(str(update_expression))
        response = ddbTable.update_item(
           Key=key,
           UpdateExpression=update_expression,
           ExpressionAttributeValues=expression_attribute_values,
           ExpressionAttributeNames=expression_attribute_names
        )
    except Exception as err:
        status_code = 400
        response_body = {"Error:": str(err)}
        print(str(err))

return {
        "statusCode": status_code,
        "body" :  response
    
    }
```

Leeroy Hannigan · Accepted Answer

This is most likely due to the fact that `data` dict does not exist in the current item you're trying to update. You cannot update `status` if it's within a dict that does not exist, you can catch the exception and add the entire dict which should provide a workaround.

```python
status = order_data['status']
orderId = order_data['orderId']
userId = order_data['userId']

key={ 
    "userId": userId,
    "orderId": orderId
}

update_expression = "SET #data.#status = :status"
expression_attribute_values = {":status": status} 
expression_attribute_names = {"#data": "data", "#status": "status"}
try:
    response = ddbTable.update_item(
        Key=key,
        UpdateExpression=update_expression,
        ExpressionAttributeValues=expression_attribute_values,
        ExpressionAttributeNames=expression_attribute_names
    )
except ClientError as e:
    if e.response['Error']['Code'] == 'ValidationException':
        expression_attribute_values = {":data": {"data":{
            "status":status
        }}} 
        expression_attribute_names = {"#data": "data"}
        update_expression = "SET #data = :data"
        response = ddbTable.update_item(
            Key=key,
            UpdateExpression=update_expression,
            ExpressionAttributeValues=expression_attribute_values,
            ExpressionAttributeNames=expression_attribute_names
        )
```

Michael WyCliffe Williams · Answer

Ensure that your update expression is correctly formatted

import boto3

dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('YourTableName')

def lambda_handler(event, context):
    response = table.update_item(
        Key={
            'PrimaryKey': event['PrimaryKey']
        },
        UpdateExpression="SET attribute1 = :val1, attribute2 = :val2",
        ExpressionAttributeValues={
            ':val1': event['value1'],
            ':val2': event['value2']
        }
    )
    return response

Attribute in DynamoDB cannot be updated by lambda function

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