ParameterVailidation Failed When Sending List to DynamoDB

Question

I have a simple Python function on AWS Lambda that just puts some data into a DynamoDB table and as far as I can tell, I'm following the correct format as per the Boto3 documentation for the put_item() function. I'm getting the following error that I can't seem to debug:

"errorMessage": 
"Parameter validation failed:\nInvalid type for parameter 
Item.GSRResults.L[0], value: 3.8, type: <class 'float'>, valid types: <class 'dict'>
\nInvalid type for parameter Item.GSRResults.L[1], value: 3.4, type: <class 'float'>, valid types: <class 'dict'>\... snip...
\nInvalid type for parameter Item.GSRResults.L[9], value: 3.3, type: <class 'float'>, valid types: <class 'dict'>",
  "errorType": "ParamValidationError",
  "stackTrace": [
    [
      "/var/task/index.py",
      39,
      "upload_test",
      "Item=item"
    ],

Here is the Python function:

def upload_test(event, context):
    if event['httpMethod'] == 'POST':
        info = event['body']
        item = info['Item']
        return respond(None, dynamo.put_item(
            TableName="TestResults",
            Item=item))

This is the JSON I am sending:

{
  "body": {
    "Item": {
      "UID": {
        "S": "U999999"
      },
      "PID": {
        "S": "P444444"
      },
      "GSRResults": { "L": [3.8,3.4,3.3,2.8,1.3,3.2,4.3,2.1,3.2,3.3] }
    }
  },
  "httpMethod": "POST"
}

@Asdfg Thanks for your response. In the documentation one of the examples they give: `"L": ["Cookies", "Coffee", 3.14159]` — empty_space, Nov 01 '17 at 17:28
that example may not be for Python. Python treats 3.8 as float while other may treat it as decimal. I guess but I could be wrong here. — Asdfg, Nov 01 '17 at 17:30
If I change these values to int's or str's I still get the same error with a different type. — empty_space, Nov 01 '17 at 17:31

jarmod · Accepted Answer · 2020-12-04T13:37:58.800

Use the following Client.put_item example for the Client API:

import boto3
client = boto3.client('dynamodb')

item1 = {
  "id": {
    "S": "1",
  },
  "name": {
    "S": "Testing"
  },
  "age": {
    "N": "22"
  },
  "grades": {
    "L": [ {"N": "3.50"}, {"N": "3.1415926"} ]
  }
}

client.put_item(TableName='test', Item=item1);

Or use the following Table.put_item example for the Resource API:

import boto3
dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('test')

item2 = {
  "id": "2",
  "name": "Testing2",
  "age": 22,
  "grades": [ decimal.Decimal('3.50'), decimal.Decimal('3.1415926') ]
}

table.put_item(Item=item2)

It's very easy to find that you are using a Resource-level object (such as Table) but accidentally looking at the Client-level API documentation because the methods unfortunately have the same names (e.g. put_item).

See a related post on when to use a boto3 Client vs a Resource. The key difference here is that the Resource API marshals/unmarshals data to/from native Python data types automatically, while the Client API does not.

This did it, thank you so much! This is my first time working with Lambda and DynamoDB so I'm still learning how to properly format all of the data. I guess when retrieving the data I would need to parse this list of dicts and get all the values in a list. Kind of inconvenient but at least this is working now. — empty_space, Nov 01 '17 at 18:19

score 1 · Answer 2 · answered Nov 01 '17 at 17:38

1

The float values should be set as demical in Python.

Import:-

import decimal

Set the value as decimal:-

"GSRResults": [decimal.Decimal('3.8'),decimal.Decimal('3.4')]

Dynamodb Type for Python

For types that involve numbers, it is recommended that Decimal objects are used to be able to round-trip the Python type.

answered Nov 01 '17 at 17:38

notionquest

37,595
6
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I tried this and it's still complaining that the type is not dict. – empty_space Nov 01 '17 at 17:52
I have tested it. It works fine for me. I don't have type "L" explicitly in the json string. My jsonString = {"storage_CACHE_KEY": "2", "GSRResults": [decimal.Decimal('3.8'),decimal.Decimal('3.4')] } – notionquest Nov 01 '17 at 17:54

ParameterVailidation Failed When Sending List to DynamoDB

2 Answers2