How to insert empty string in DynamoDB using the output of a Lambda in Step Functions?

Question

I'm trying to save the output of a Lambda which calls Lex to DynamoDB using Step Functions.

The intentName in a Lex response is sometimes null (unknown). The problem is that in the state (task) that saves the response to DynamoDB, because of this empty string I get an error from DynamoDB.

Is there any workaround, maybe using JsonPath or the state machine diagram of the Step Function, in order to insert null or maybe no insert that specific property in DynamoDB?

Here is the JSON for the state machine:

{
  "StartAt": "ProcessLex",
  "States": {
    "ProcessLex": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:<Region>:<Account Id>:function:getIntent",
      "ResultPath": "$.lexResult",
      "Next": "ChoiceIfIntent"
    },
    "SaveToDynamo": {
      "Type": "Task",
      "Resource": "arn:aws:states:::dynamodb:putItem",
      "Parameters": {
        "TableName": "MyTable",
        "Item": {
          "dateTime": {
            "S.$": "$.dateTime"
          },
          "intentName": {
            "S.$": "$.lexResult.intentName"
          },
          "analysis": {
            "M.$": "$.lexResult.sentimentResponse"
          }
        }
      },
      "End": true
    },
    "Comprehend": {
      "Comment": "To be implemented later",
      "Type": "Pass",
      "End": true
    },
    "ChoiceIfIntent": {
      "Type": "Choice",
      "Choices": [
        {

            "Variable": "$.lexResult.intentName",
            "StringGreaterThanEquals": "",

          "Next": "SaveToDynamo"
        }        
      ],
        "Default": "Comprehend"
    }
  }
}

I'm guessing it's not longer a problem since May 18, 2020 – Dima Tisnek May 20 '20 at 04:18 — Dima Tisnek, May 20 '20 at 04:18

desoss · Accepted Answer · 2020-05-19T09:26:38.727

0

The problem is not the null value, the problem is that in DynamoDB with the PutItem Api you cannot insert empty strings.

I know this is frustrating but the quickest solution is to replace "" with NULL.

The solution that I prefer is to set the convertEmptyValue to true in your DynamoDb client settings.

const dynamodb = new AWS.DynamoDB.DocumentClient({ convertEmptyValues: true })

UPDATE

Since yesterday, DynamoDB supports empty values for string! Take a look here.

edited May 19 '20 at 09:26

answered May 07 '20 at 00:01

desoss

572
4
26

Thanks you!. I've seen this solution, but the problem is that I'm using **Step Functions**, meaning that the output from Lex is saved in DynamoDB using states, I don't have direct access to the DynamoDB SDK. I'll put the JSON for the state machine above. – eldercookie May 07 '20 at 16:56
@eldercookie take a look at the link that I've added in the answer. Now your issue should be solved! – desoss May 19 '20 at 09:27
1

Thank you very much!. I'm going to try it and tell how it went. – eldercookie May 19 '20 at 16:14
Apparently they fixed it on May 18, 2020 – Dima Tisnek May 20 '20 at 04:17
@DimaTisnek as I wrote in the answer – desoss May 20 '20 at 12:57

How to insert empty string in DynamoDB using the output of a Lambda in Step Functions?

1 Answers1