dynamodb how to query by sort key only?

Question

I have written some python code, I want to query dynamoDB data by sort key. I remember I can use follow-up code successful:

 table.query(KeyConditionExpression=Key('event_status').eq(event_status))

My table structure column

primary key:event_id
sort key: event_status

Answer 1

You have to create a global secondary index (GSI) for the sort key in order to query on it alone.

Answer 2

The scan API should be used if you would like to get data from DynamoDB without using Hash Key attribute value.

Example:-

fe = Attr('event_status').eq("new");

response = table.scan(
        FilterExpression=fe        
    )

for i in response['Items']:

print(json.dumps(i, cls=DecimalEncoder))

while 'LastEvaluatedKey' in response:
    response = table.scan(        
        FilterExpression=fe,        
        ExclusiveStartKey=response['LastEvaluatedKey']
        )

    for i in response['Items']:
        print(json.dumps(i, cls=DecimalEncoder))

Answer 3

If you don't want to scan (and maybe you shouldn't), you will need to create a GSI (Global Secondary Index) for that, and set event_status as the GSIPK.

so your table config will be:

 table = dynamodb.create_table(
        TableName="your_table",
        KeySchema=[
            {"AttributeName": "event_id", "KeyType": "HASH"},  # Partition key
            {"AttributeName": "event_status", "KeyType": "RANGE"},  # Sort key
        ],
        AttributeDefinitions=[
            {"AttributeName": "event_id, "AttributeType": "S"},
            {"AttributeName": "event_status", "AttributeType": "S"},
            {"AttributeName": "event_status", "AttributeType": "S"},
            {"AttributeName": "event_id", "AttributeType": "S"},
        ],
        GlobalSecondaryIndexes=[
            {
                "IndexName": "gsiIndex",
                "KeySchema": [
                    {"AttributeName": "event_status", "KeyType": "HASH"},
                    {"AttributeName": "event_id", "KeyType": "RANGE"},
                ],
                "Projection": {"ProjectionType": "ALL"},
            },
        ],
        BillingMode="PAY_PER_REQUEST",
    )

Be mindful that GSIs can be expensive and you might wanna change the ProjectionType if you don't need all attributes.

Now you can query by pk:

table.query(KeyConditionExpression=Key('event_id').eq(event_id))

or by the GSI PK which is set to your sk:

lookup.query(
        IndexName="gsiIndex",
        KeyConditionExpression=Key("event_status").eq(event_status),
    )

Answer 4

According to the main concept of the sort key, it is part of main cluster in the partition key to define some filter expression with partition key in query. so there is no ability to search on the sort key alone and without partition key. unless to define a global secondary index on the sort key.