Paginate response on DynamoDB-API Gateway with ExclusiveStartKey

Question

I'm building an API that retrieves a batch of records from my Dynamo DB. I'm using Scan action.

My request has a FilterExpression around the field "wb_date". If the request is too large, the API response will show the parameter LastEvaluatedKey which allows me to make a subsequent request to retrieve another batch of data.

This is the mapping request:
```
{
    "TableName": "Test",
    "Limit": 10000,
    "FilterExpression": "wb_date = :val",
    "ExpressionAttributeValues": {
        ":val": {
            "S": "$input.params('wb_date')"
        }
    },
    "ExclusiveStartKey": {
        "salesforce_id": {
            "S": "$input.params('salesforce_id')"
        },
        "type": {
            "S": "$input.params('type')"
        }
    },
    "ReturnConsumedCapacity": "TOTAL"
}
```

**My issue is:  I don't know how to make the first request since the API is forcing me to pass something on the ExclusiveStartKey  fields (salesforce_id and type)**

I wish I could pass 0 on both parameters https://i.imgur.com/ti9KhgA.png. It works but the Scan does not starts on the first record. The Scan seems to start far away from my 1st record.

Is there a wildcard or a workaround to make this first API call go and Scan from the beginning?

Thank you in advance

Lucas · Accepted Answer

Found the Answer after iterating with ChatGpt.

I had to rewrite my mapping request with an If clause.

If salesforce_id = 0, send the request with no ExclusiveStartKey field.
Else, send the request with the ExclusiveStartKey fielda.

```
{
    "TableName": "Test-Table",
    "Limit": 100,
    "FilterExpression": "wb_date = :val",
    "ExpressionAttributeValues": {
        ":val": {
            "S": "$input.params('wb_date')"
        }
    },
    #if($input.params('salesforce_id') == "0")
        "ReturnConsumedCapacity": "TOTAL"
    #else
        "ExclusiveStartKey": {
            "salesforce_id": {
                "S": "$input.params('salesforce_id')"
            },
            "type": {
                "S": "$input.params('type')"
            }
        },
        "ReturnConsumedCapacity": "TOTAL"
    #end
}

```

James_S · Answer

`ExclusiveStartKey` isn't a required parameter in the request structure so you should be able to omit it entirely for your initial request.

Reference: https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Query.html#DDB-Query-request-ExclusiveStartKey

Paginate response on DynamoDB-API Gateway with ExclusiveStartKey

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