REST API - Retrieve previous query in dynamoDB

Question

I have 100 rows of data in DynamoDB and a api with path api/get/{number}

Now when I say number=1 api should return me first 10 values. when I say number=2 it should return next 10 values. I did something like this with query, lastEvaluatedKey and sort by on createdOn . Now the use case is if the user passes number=10 after number=2 the lastEvaluatedKey is still that of page 2 and the result would be data of page 3. How can I get data directly. Also if the user goes from number=3 to number=1 still the data will not be of page 1.

I am using this to make API call based of pagination on HTML.

I am using java 1.8 and aws-java-sdk-dynamodb .

Answer 1

Non-sequential pagination in DynamoDB is tough - you have to design your data model around it, if it's an operation that needs to be efficient at all times. For a recommendation in your specific case I'd need more details about the data and access patterns.

In general you have the option of setting the ExclusiveStartKey attribute in the query call, which is similar to an offset in relational databases, but only similar and not identical. The ExclusiveStartKey is the key after which the query will continue, meaning data from your table and not just a number.

That means you usually can't guess it, unless it's a sequential number - which isn't ideal.

For sequential pagination, ie the user goes from page 1 to page 2, page 2 to page 3 etc. you can pass that along in the request as a token, but that won't work if the user moves in the other direction page 3 to page 2 or just randomly navigates to page 14.

In your case you only have a limited amount of data - 100 items, so my solution for your specific case would be to query all items and limit the amount of items in the response to n * 10 , where n is the result page. Then you return the last 10 items from that result to your client.

This is a solution that would get expensive at scale (time + cost) though, fortunately not many people will use the pagination to go to page 7 or 8 though ( you could bury a body on page 2 of the google search results ).

Yan Cui has written an interesting post on this problem on Hackernoon , you might want to check it out.