Question 19517 in Amazon Web Sevices Question posted in
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Lambda event filtering for DynamoDB trigger

Here is a modified version of an Event type I am receiving in my handler for a lambda function with a DynamoDB someTableName table trigger that I logged using cargo lambda.

Event { 
    records: [
        EventRecord { 
            change: StreamRecord { 
                approximate_creation_date_time: ___ 
                keys: {"id": String("___")}, 
                new_image: {
                   ....
                    "valid": Boolean(true), 
                }, 
               ...
            }, 
            ...
            event_name: "INSERT", 
            event_source: Some("aws:dynamodb"), 
            table_name: None 
        }
    ] 
}

Goal: Correctly filter with event_name=INSERT && valid=false

I have tried a number of options, for example;
{"eventName": ["INSERT"]}
While the filter is added correctly, it does not trigger the lambda on item inserted.

Q1) What am I doing incorrectly here?

Q2) Why is table_name returning None? The lambda function is created with a specific table name as trigger. The returned fields are returning an option (Some(_)) so I’m asssuming it returns None if the table name is specified on lambda creation, but seems odd to me?

Q3) From AWS Management Console > Lambda > … > Trigger Detail, I see the following (which is slightly different from my code mentioned above), where does "key" come from and what does it represent in the original Event?

enter image description here

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2

Answers


  1. 0

    The attribute name is actually eventName, so your filter should look like this:

    {"eventName": ["INSERT"]}
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  2. 0

    Filters must follow the documented syntax for filtering in the Event Source Mapping between Lambda and DynamoDB Streams.

    If you are entering the filter in the Lambda console:

    { "eventName": ["INSERT"], "dynamodb": { "NewImage": {"valid": { "BOOL" : [false]}} } }
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