Is it possible to run a Lambda function as part of a GetItem / Query request? I plan to use some kind of computed colum that I would like to update before the value is returned to the caller. The current idea is to do this with a Lambda function and DynamoDB Streams. Up to know, I kind of missed the part in the docs where I can specify the exact moment when the Lambda is executed (before, after fetching data). Of course, I am open for better ideas!
No. It is not possible. Dynamodb is designed to response items in distributed systems within milliseconds. There is no way to execute Lambdas synchronous with Put or Get Requets. DynamodDB Streams are more like asynchronous Table Trigger and only executed on new Data.
One Idea is to call an Lambda to collect and compute your data instead request Dynamodb.