Scan Dynamo DB using ExclusiveStartKey to return the 1st record that matches the filter

Question

Hello there. I'm having this challenge where my Scan request mapping looks like this:
```
{
    "TableName": "Test-Table",
    "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 request and response are retrieving the data. However, I need to know how to make that first API Call to retrieve the first matching record. If I pass 0 on my request https://i.imgur.com/qDZeBpf.png, the data returned starts from any other record than the first value of the DynamoDB.

Since this is my 1st API call, I do not know what values to add in the ExclusiveStartKey params (salesforce_id and type). So my question aims to know if there is some sort of wildcard or default value to retrieve the data from the default 1st record found. Then, I can continue to retrieve based on the LastEvaluatedKey response.

Thanks!

Answer

Since the ExclusiveStartKey attribute is optional. I just had to modify mi API request mapping by removing the ExclusiveStartKey like this:

```
{
    "TableName": "Test-Table",
    "Limit": 10000,
    "FilterExpression": "wb_date = :val",
    "ExpressionAttributeValues": {
        ":val": {
            "S": "$input.params('wb_date')"
        }
    },
      "ReturnConsumedCapacity": "TOTAL"
}
```
Despite removing it, the API still process it when I consume it with 0 value or with a real Id value

Answer

The "ExclusiveStartKey" setting is optional.  
So, it is not necessary to specify it at the very first execution.  
LastEvaluatedKey is included in the response when all data could not be retrieved during the first scan.  
The first run will scan without specifying ExclusiveStartKey.  
If the response from the first run contains LastEvaluatedKey, put a value in ExclusiveStartKey and run it again.  
So I think you need to change the content of your API a bit.  
https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Scan.html

Scan Dynamo DB using ExclusiveStartKey to return the 1st record that matches the filter

Relevant content