Dynamodb scan in sorted order

Question

Hi I have a dynamodb table. I want the service to return me all the items in this table and the order is by sorting on one attribute.

Do I need to create a global se

Answer 1

As of now the dynamoDB scan cannot return you sorted results.

You need to use a query with a new global secondary index (GSI) with a hashkey and range field. The trick is to use a hashkey which is assigned the same value for all data in your table.

I recommend making a new field for all data and calling it "Status" and set the value to "OK", or something similar.

Then your query to get all the results sorted would look like this:

{
    TableName: "YourTable",
    IndexName: "Status-YourRange-index",
    KeyConditions: {
        Status: {
            ComparisonOperator: "EQ", 
            AttributeValueList: [ 
                "OK"
            ]
        }
    },
    ScanIndexForward: false
}

The docs for how to write GSI queries are found here: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/GSI.html#GSI.Querying

Answer 2

Approach I followed to solve this problem is by creating a Global Secondary Index as below. Not sure if this is the best approach but posting it if it is useful to someone.

Hash Key                 | Range Key
------------------------------------
Date value of CreatedAt  | CreatedAt

Limitation imposed on the HTTP API user to specify the number of days to retrieve data, defaults to 24 hr.

This way, I can always specify the HashKey as Current date's day and RangeKey can use > and < operators while retrieving. This way the data is also spread across multiple shards.

Answer 3

If you know the HashKey, then any query will return the items sorted by Range key. From the documentation:

Query results are always sorted by the range key. If the data type of the range 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 set to false.

Now, if you need to return all the items, you should use a scan. You cannot order the results of a scan.

Another option is to use a GSI (example). Here, you see that the GSI contains only HashKey. The results I guess will be in sorted order of this key (I didn't check this part in a program yet!).