Using a ProjectionExpression with reserved words with Boto3 in DynamoDB

Question

I’m selecting data from my DynamoDB database using boto3

dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table(table_name)
response = table.scan(ProjectionExpression='Id,Name')['Items']

Works fine. Now I also want to retrieve an attribute that is (unfortunately) named with a reserved word – let’s say CONNECTION.

response = table.scan(ProjectionExpression='Id,Name,Connection')['Items']

I get an error like

An error occurred (ValidationException) when calling the Scan
operation: Invalid ProjectionExpression: Attribute name is a reserved
keyword; reserved keyword: Connection

I know there’s an aliasing technique if using filters or queries, but does this exist for simple projections from boto3?

Asked By: Kirk Broadhurst

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Source

Answer 1

Turns out that this is easily solved the same as when calling the DynamoDB API directly.

We should use an alias for any reserved word, and then provide a mapping from the alias back to the ‘true’ name with the ExpressionAttributeName parameter/property.

response = table.scan(ProjectionExpression = 'Id, Name, #c',
                      ExpressionAttributeNames = {'#c': 'Connection'})['Items']

Answered By: Kirk Broadhurst

Using a ProjectionExpression with reserved words with Boto3 in DynamoDB

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