AWS Lambda python boto3 dynamodb table scan - An error occurred (ValidationException) when calling the Scan operation: ExpressionAttributeNames

Question

I am writing a simple dynamodb table scan with a filter expression using the boto3 documentation https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/dynamodb.html#DynamoDB.Table.scan

I am getting this error: { "errorMessage": "An error occurred (ValidationException) when calling the Scan operation: ExpressionAttributeNames can only be specified when using expressions", "errorType": "ClientError", Code: import boto3 import pprint from pprint import pprint from boto3.dynamodb.conditions import Key from boto3.dynamodb.conditions import Attr

    dbresource =boto3.resource('dynamodb')

    def lambda_handler(event, context):

    tableobject = dbresource.Table('basicSongsTable')

    response = tableobject.scan(ExpressionAttributeNames={'artist': ':variableartist'},
                            ExpressionAttributeValues={':variableartist': {'S': 'Matt'}})

    pprint(response)

Leeroy Hannigan · Accepted Answer · 2022-10-04 23:33:40Z

3

I'm guessing you want to Scan the table and return when the artist=Matt?

dbresource =boto3.resource('dynamodb')

    def lambda_handler(event, context):

    tableobject = dbresource.Table('basicSongsTable')

    response = tableobject.scan(
    ExpressionAttributeNames={'#a': 'artist'},
    ExpressionAttributeValues={':v': {'S': 'Matt'}},
    FilterExpression='#a=:v'
    )

    print(response)

More examples here: https://github.com/aws-samples/aws-dynamodb-examples/tree/master/DynamoDB-SDK-Examples/python/WorkingWithScans

answered Oct 4, 2022 at 23:33

Leeroy Hannigan

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3 Comments

Jason Over a year ago

Thank You so much. I don't know why they made it so complex. we need 3 parameter to scan a table. Greatly appreciate Your response

Jason Over a year ago

I clicked on that Ok arrow. Isn't that accepted ? Let me know if I need to click on something else

Jason Over a year ago

I looked at Your github samples. Great resource. I hope You teach on Udemy

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