Not able to get_item from AWS dynamodb using python?

Question

I am new to dynamodb trying to get data from dynamodb.

This is my table with "topic" as a primary hash key

my python code

import boto3 
from boto3 import dynamodb 

from boto3.session import Session

from boto3.dynamodb.conditions import Key, Attr


dynamodb_session = Session(aws_access_key_id='XXXXXXXXXXXXXXX',
          aws_secret_access_key='XXXXXXXXXXXXXXXXXXXXXXXXXXXX',
          region_name='us-east-1')

dynamodb = dynamodb_session.resource('dynamodb')

table=dynamodb.Table('Garbage_collector_table')

my_topic = "$aws/things/garbage_collector_thing/shadow/update/accepted"

response = table.get_item(TableName='Garbage_collector_table', Key={'topic':my_topic})

for res in response: 
    print "result ",res

I am getting the following error

Traceback (most recent call last):
 File "get-data-dynamodb-boto3.py", line 19, in <module>
    response = table.get_item(TableName='Garbage_collector_table', Key={'topic': my_topic})   File
 "/usr/local/lib/python2.7/dist-packages/boto3/resources/factory.py",
 line 518, in do_action
     response = action(self, *args, **kwargs)   File "/usr/local/lib/python2.7/dist-packages/boto3/resources/action.py",
 line 83, in __call__
     response = getattr(parent.meta.client, operation_name)(**params)   File "/usr/local/lib/python2.7/dist-packages/botocore/client.py", line
 258, in _api_call
     return self._make_api_call(operation_name, kwargs)   File /usr/local/lib/python2.7/dist-packages/botocore/client.py", line 548,
 in _make_api_call
     raise ClientError(parsed_response, operation_name)

botocore.exceptions.ClientError: An error occurred (ValidationException) when calling the GetItem operation: The provided key element does not match the schema

am I missing anything in my code?

Answer 1

You are mixing resource and client objects which have different methods. More info here.

The correct syntax for a resource is:

response = table.get_item(Key={'topic': my_topic})

but personally I recommend to use boto client:

client = boto3.client('dynamodb')

response = client.get_item(TableName='Garbage_collector_table', Key={'topic':{'S':str(my_topic)}})

http://boto3.readthedocs.io/en/latest/reference/services/dynamodb.html

Answer 2

You can also query the database:

from boto3.dynamodb.conditions import Key

table = dynamodb.Table(table_name)
response = table.query(
    KeyConditionExpression=Key('topic').eq(my_topic)
)
items = response['Items']
if items:
    return items[0]
else:
    return []

Source: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/GettingStarted.Python.04.html