CODEWITHSUNDEEP
amazon-web-servicesamazon-dynamodbaws-api-gateway
Geert-Jan
Geert-Jan

Reputation: 18905

defining optional attribute in AWS Api Gateway -> DynamoDB mapping

I'm following along: Using Amazon API Gateway as a proxy for DynamoDB

Taking the blog's example, I want to tighten what and how data is written to a dynamodb table frontend by Api Gateway. To this end I define the following mapping in Api Gateway:

{ 
    "TableName": "Comments",
    "Item": {
      "commentId": {
        "S": "$context.requestId"
       },
       "pageId": {
         "S": "$input.path('$.pageId')"
       },
       "userName": {
         "S": "$input.path('$.userName')"
       },
       "message": {
         "S": "$input.path('$.message')"
       }
    }
}

Following along, testing with the following example works just fine: 

{
  "pageId": "breaking-news-story-01-18-2016",
  "userName": "Just Saying Thank You",
  "message": "I really enjoyed this story!!"
}

However, let's say I want to keep the same mapping as above but want to make message optional. How would I do that? I can't get it to work. I've tried:

  1. using the above mapping as is, but sending a body without the message-attribute. --> "One or more parameter values were invalid: An AttributeValue may not contain an empty string" 2 using the above mapping as is, but sending a body with message=null. --> "One or more parameter values were invalid: An AttributeValue may not contain an empty string"
  2. changing above mapping by omitting the definition for mapping -> passing a body now without message succeeds obviously. However, sending a body with message doesn't pass message through (which is what I expected, but wanted to exhaust all options)
  3. Don't use a mapping at all. Obviously that works, but now everything is passed-through unfiltered, which is unwanted.

Obviously I could use AWS lambda instead to do the mapping but this feels like such a common use-case, i.e.: optional attributes, that this must be possible directly in Api Gateway.

Upvotes: 1

Views: 1706

Answers (2)

Geert-Jan
Geert-Jan

Reputation: 18905

Courtesy of @ka:

Explatation: APi gateway auto-populates non-existing attributes with empty strings or something. This needs to be excluded from the if.

Also notice the critical , right after the if statement. 

{ 
    "TableName": "Comments",
    "Item": {
      "commentId": {
        "S": "$context.requestId"
       },
       "pageId": {
         "S": "$input.path('$.pageId')"
       },
       "userName": {
         "S": "$input.path('$.userName')"
       }#if($input.path('$.description') && $input.path('$.message') != ""),
       "message": {
         "S": "$input.path('$.message')"
       }
       #end
    }
}

Upvotes: 2

Ka Hou Ieong
Ka Hou Ieong

Reputation: 6515

Would you mind trying this mapping template? If the message is NULL, it will not be added to the body.

{ 
    "TableName": "Comments",
    "Item": {
      "commentId": {
        "S": "$context.requestId"
       },
       "pageId": {
         "S": "$input.path('$.pageId')"
       },
       "userName": {
         "S": "$input.path('$.userName')"
       }#if ($.message),
       "message": {
         "S": "$input.path('$.message')"
       }
       #end
    }
}

Thanks, -Ka Hou

Upvotes: 0

Related Questions