Amazon lambda dynamodb update_item() 只接受关键字参数

Question

I am trying to save data in dynamodb using update_item for the first time. In another area of my project I have used put_item() successfully. For this new area of code I am saving only items that change, leaving items in the db that are unchanged. Thus, I need to use update_item(). However, I can't seem to figure out why my syntax is not correct for the API call. I am using this directly from the Amazon UI.

Here is my python code:

from __future__ import print_function
import json
import boto3

print('Loading function')

def saveScreenData(event, context):

    dynamodb = boto3.client('dynamodb', region_name='us-east-1', endpoint_url="https://dynamodb.us-east-1.amazonaws.com")

    print('The event: {}'.format(event))

    key = {}
    key['UID'] = event['uid']
    key['screenId'] = event['screenid']
    print('Key: {}'.format(key))

    for item, val in event.items():

        if item != 'uid' and item != 'screenid':
            print("Saving!")
            response = dynamodb.update_item({ 
                "TableName" : "ScreenData",
                "Key" : key,
                "UpdateExpression" : "SET #attrName = :attrValue",
                "ExpressionAttributeNames" : {
                    "#attrName" : item
                },
                "ExpressionAttributeValues" : {
                    ":attrValue" : val
                }
            })

            print('Response: {}'.format(response))


    return response

Here is the output:

START RequestId: 2da9412a-b03d-11e7-9dc8-8fcb305833f6 Version: $LATEST
The event: {'article': '<p>↵    First!↵</p>', 'screenid': '13', 'uid': '0', 'section1': '<h1>↵    Second↵</h1>'}
Key: {'UID': '0', 'screenId': '13'}
Saving!
update_item() only accepts keyword arguments.: TypeError
Traceback (most recent call last):
  File "/var/task/saveScreenData.py", line 30, in saveScreenData
    ":attrValue" : val
  File "/var/runtime/botocore/client.py", line 310, in _api_call
    "%s() only accepts keyword arguments." % py_operation_name)
TypeError: update_item() only accepts keyword arguments.

END RequestId: 2da9412a-b03d-11e7-9dc8-8fcb305833f6

I have researched the update_item docs ( https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_UpdateItem.html ) and have modeled my query after this SO q&a by mkobit ( https://stackoverflow.com/users/627727/mkobit ): https://stackoverflow.com/a/30604746/8027640

I have played with variations on the syntax, including adding the dictionary {"S" : "maybe this works"} instead of my variable val, and have also tried changing the variable to some static content to see if it works, but no luck.

Clearly this is a syntax issue, but I have been unable to track it down. Suggestions?

Answer 1

I think the example your are using is based on boto2 which has quite different interface comparing to boto3 .

Instead, look into the boto3 documentation , you should use keyword arguments as the error states (and you are using the dictionary). Your request should look approximately like this:

response = dynamodb.update_item(
    TableName="ScreenData",
    Key=key,
    UpdateExpression="SET #attrName = :attrValue",
    ExpressionAttributeNames={
        "#attrName" : item
    },
    ExpressionAttributeValues={
        ":attrValue" : val
    }
)