Using a ProjectionExpression with reserved words with Boto3 in DynamoDB

19
votes

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?

1
pythonamazon-dynamodbboto3

1 Answers

49
votes

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']