boto3 query(): LastEvaluatedKey works, but not as documented

[StrangeHairyCreature]

Describe the issue

See https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/dynamodb/client/query.html
It says that

The data type for ExclusiveStartKey must be String, Number, or Binary. No set data types are allowed.

This is just-plain-wrong, and looks like a fossil from an earlier version of the API. The type should match LastEvaluatedKey (dict) in the response, which is indeed a dict for me.

The description given on the page for LastEvaluatedKey could be just a little clearer:

(a)
The primary key of the item where the operation stopped, inclusive of the previous result set. Use this value to start a new operation, excluding this value in the new request.

This may as well say explicitly that it's suitable for use as an ExclusiveStartKey value, which is clearly what
it means.

(b)
If LastEvaluatedKey is empty, then the “last page” of results has been processed and there is no more data to be retrieved.

This sounds like returning an empty dictionary. I find it returns None.

Links

https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/dynamodb/client/query.html

[RyanFitzSimmonsAK]

Hi @StrangeHairyCreature, thanks for reaching out.

This is just-plain-wrong, and looks like a fossil from an earlier version of the API. The type should match LastEvaluatedKey (dict) in the response, which is indeed a dict for me.

I believe this is referring to the underlying DynamoDB data type, not the Python data type. This operation queries the partition keys, and partition keys need to be a String, a Number, or a Binary.

This may as well say explicitly that it's suitable for use as an ExclusiveStartKey value, which is clearly what
it means.

I do agree this would benefit from clarity, but I would mention that the description for ExclusiveStartKey mentions this very clearly.

The primary key of the first item that this operation will evaluate. Use the value that was returned for LastEvaluatedKey in the previous operation.

This sounds like returning an empty dictionary. I find it returns None.

In my testing, when I've reached the end of the results, LastEvaluatedKey is completely absent from the response.

The Boto3 documentation for this operation is defined by the model file, which is owned by the service team. In general, the best way to provide feedback to service teams about their documentation is the "Give us feedback" on the operation page. That cuts a ticket directly to the relevant service team. Please let me know if you have any follow-up questions.

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