AWS Lambda returning JSON data as string

Question

I am using AWS Lambda to create my APIs and want to return an array's data in JSON format. However, when I call the lambda, it is able to return the required JSON data but it is coming as a string in double quotes. I tried running the same code in my Python IDE and everything works fine but when I try to return it in Lambda it is coming as a string. Has this got something to do with how Lambda handles the return statement in Python functions? This is how I'm returning data in my Lambda:

return {
            'statusCode': 200,
            'headers': {
            "Access-Control-Allow-Origin": "*",
            "Access-Control-Allow-Methods": 'GET, POST, PUT, DELETE, OPTIONS'
            },
            'body': json.dumps(json_data,default = myconverter)
        }

Here json_data is a python list which is populated with the data that is being retrieved from the database for the specific unique ID passed by the user and myconverter is the JSON encoder that I've written.

The output that I'm getting is:

{
  "statusCode": 200,
  "headers": {
    "Access-Control-Allow-Origin": "*",
    "Access-Control-Allow-Methods": "GET, POST, PUT, DELETE, OPTIONS"
  },
  "body": "[{\"Dp_Record_Id\": 2, \"DP_TYPE\": \"NSDL\", \"DP_ID\": \"40877589\", \"CLIENT_ID\": \"1232\", \"Default_flag\": \"Y\"}]"
}

Here, I want the "body" to just return an array of the data without double quotes, like this:

"body": [{\"Dp_Record_Id\": 2, \"DP_TYPE\": \"NSDL\", \"DP_ID\": \"40877589\", \"CLIENT_ID\": \"1232\", \"Default_flag\": \"Y\"}]

Please let me know if this is possible and how can it be done. Any help on this would be appreciated

Marcin · Accepted Answer · 2020-04-17 10:57:48Z

9

I'm not sure if this is what you want, but you can just do 'body': json_data. I tested this now in my λ function:

Lambda function

import json

def lambda_handler(event, context):

    json_data = [{"Dp_Record_Id": 2, 
                  "DP_TYPE": "NSDL",
                  "DP_ID": "40877589", 
                  "CLIENT_ID": "1232", 
                  "Default_flag": "Y"}]

    return {'statusCode': 200,
            'headers': {
            "Access-Control-Allow-Origin": "*",
            "Access-Control-Allow-Methods": 'GET, POST, PUT, DELETE, OPTIONS'
            },
            'body': json_data
        }

Result

Response:
{
  "statusCode": 200,
  "headers": {
    "Access-Control-Allow-Origin": "*",
    "Access-Control-Allow-Methods": "GET, POST, PUT, DELETE, OPTIONS"
  },
  "body": [
    {
      "Dp_Record_Id": 2,
      "DP_TYPE": "NSDL",
      "DP_ID": "40877589",
      "CLIENT_ID": "1232",
      "Default_flag": "Y"
    }
  ]
}

answered Apr 17, 2020 at 10:57

Marcin

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1 Comment

r42 Over a year ago

Thanks for the help, I forgot to mention that the data stored in the json_data dictionary is being populated by my SQL query. Have editted the question, please view it

anupsabraham · Accepted Answer · 2022-03-29 11:43:18Z

4

I ran into the same issue while I was creating an API by doing things from my memory. Posting this answer for my future self and others.

The issue was that whatever I return in the lambda is getting passed as response to the API. Instead only the data inside body should be passed as response.

This was happening because when I created the resource I forgot to check the checkbox to Use Lambda Proxy Integration. Here is what you have to do:

Delete your existing method and create a new one. This time make sure you check Use Lambda Proxy Integration.
Create a deployment to your stage. Until this is done, the change will not reflect. This is where I got stuck and spend most of my time.

answered Mar 29, 2022 at 11:43

anupsabraham

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Comments

Cblopez · Accepted Answer · 2020-04-17 10:55:44Z

2

Maybe the client is not understanding the type correctly, try adding the following into the "headers" dictionary:

"content-type":"application/json",

answered Apr 17, 2020 at 10:55

Cblopez

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