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Ross Barbish
Ross Barbish

Reputation: 679

AWSDynamoDBQueryExpression order by UNIX timestamp

I am new to NoSQL databases and I have changed my database schema from storing dates as a UTC timestamp string, to a UNIX timestamp (number), in hopes that I can create either a scan or a query expression to find the 1000 most recent items in the table. I have yet to find a simple snippet of code to accomplish this using the AWSDynamoDBQueryExpression class. Scan doesn't appear to have any sort mechanism but query might. Any ideas?

Upvotes: 0

Views: 413

Answers (2)

Mike Dinescu
Mike Dinescu

Reputation: 55730

There is no ORDER BY functionality in DynamoDB. If you want to run a top N query you'll have to performa a scan and then order the results yourself.

Mark B is right that query results can be ordered by the sort key but that is only within the context of a query. Queries are inherently limited to a single partition key.

If your table is small then you can get away with creating a Global Secondary Index on the table in which the partition key can be an attribute that is the same for all items and then use the timestamp attribute as a sort key. But keep in mind that this will break down once your table gets bigger. And if you're doing that you might as well not be using Dynamo. You're better off with an relational database on RDS.

Upvotes: 1

Mark B
Mark B

Reputation: 200712

First you need to make sure the timestamp field is the sort key for your DynamoDB table (or the sort key for a Global Secondary Index on that table). Then you just need to run a query. From the documentation:

Query results are always sorted by the sort key value. If the data type of the sort key is Number, the results are returned in numeric order; otherwise, the results are returned in order of UTF-8 bytes. By default, the sort order is ascending. To reverse the order, set the ScanIndexForward parameter to false.

Upvotes: 1

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