KeyConditions and KeyConditionExpression fail in Python

Question

I am trying to modify the lambda-microservice example to submit a GET query to dynamodb from an aws-api-gateway. I have gotten the example to work but it does a table scan, not a query.

The query fails trying to set the KeyConditionExpression with the following message: "Lambda execution failed with status 200 due to customer function error: name 'Key' is not defined."

The relevant python is here:

     operations = {
         'GET': lambda dynamo, x: dynamo.query(**x),
     }

    dynamodb = boto3.resource('dynamodb')

    params = {
    'KeyConditionExpression': Key('flight').eq("2002")     
    }

table = dynamodb.Table('Test')
response = table.query(params)

This query form is the same one that worked in this posting:

[Working query][1]

and I got the same error above.

Alternatively, I get a different error when I try to set the KeyConditions: "Lambda execution failed with status 200 due to customer function error: An error occurred (ValidationException) when calling the Query operation: Either the KeyConditions or KeyConditionExpression parameter must be specified in the request.. "

The relevant python is here:

    params = {
    'TableName': 'Test',
    'KeyConditions': {
        "flight": {
            'ComparisonOperator': "EQ",
            'AttributeValueList': [{'S': '2002'}]
        }
    }
}

My table (Test) has a GSI index, flight-index, with flight as a partition key and the items (all type string) are simply these:

A different post said: "KeyConditionExpression is not supported with nodejs SDK." Is there any similar problem with my using Python 3.7?

Also I am not running DynamoDB local. (I'm grasping at straws for clues.)

As simple as this whole test case is, I must be missing something awfully simple, but I have struggled for several days and read dozens of posts to find it.

Can someone help make either of these ways of specifying the query target work?

JAW · Accepted Answer · 2019-03-19 20:50:54Z

2

There were a couple of different issues that complicated my problem. I presume no one answered because there wasn't an obvious fix.

What I had to do:

Import Key python library: Many thanks to @user3303554 for the advice in this answer to import Key from boto3.dynamodb.conditions import Key
DynamoDB query permission: That finally gave me an AccessDeniedException that showed my lambda function did not have permission to query DynamoDb. Many additional thanks to @Lisa M Shon in this answer for pointing me to http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/using-identity-based-policies.html because that showed that the microservice example I started modifying had read/write perms, but it did not have a query perm. Added that to the role, and it worked like a charm.

Hopes this helps somebody else just trying to do a simple DynamoDB query.

answered Mar 19, 2019 at 20:50

JAW

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1 Comment

user1832464 Over a year ago

Import Key is the winner here - I too was struggling with this.

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