DynamoDB query & partition keys, simple question

Question

something I don't understand about querying a dynamoDB table is that it seems necessary to include something like .withKeyConditionExpression("itemId = :v_id"), but since the partition key uniquely identifies all items in the table, wouldn't you always be searching just one result?

Trying to do something like:

val expression = DynamoDBQueryExpression<PluginItem>()
                .withKeyConditionExpression("itemId > 0")
                .withFilterExpression("attributes.item_modification_date < :val1")
                .withExpressionAttributeValues(eav)
val paginatedResults = queryByExpression(expression)

I'm looking to query and paginate 100,000 items in the table, can anyone point me in the right direction?

Neil · Accepted Answer · 2019-03-06 21:24:28Z

partition key uniquely identifies all items in the table

so this isn't accurate. It depends on your table design. However, you will get a lot more fexibility if you design a table with a ParitionKey and a Sort Key. That said, back to your statement. A Primary Key not a partition key uniquely identifies an item in the table. A primary key is a combination of ParitionKey + SortKey(also known as Range Key).

Think of each partition as a bucket.

withKeyConditionExpression("itemId > 0")

this won't work. You can't do those kinds of operations on a partition key. However, you can do those kinds of conditions on a sort key.

a video from 2018 - re:Invent that helped me get a better understanding of Dynamo. I have watched that video quite a few times, especially the last 30 to 20mins of it.

Hope that helps. I have only been working with dynamodb for a few months and there is so much more I have to learn.

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