如何使用DynamoDB表中的数据在AWS云中进行算术运算（+，-，/，*，％）

Question

Can some one help me and please let me know,Which tool in AWS I should use to perform math operations such as add/sub/mul/div/mod etc with data inside a dynamodb table? Currently I am hosting my data inside DynamoDB via raspberry Pi using python as my programming language. But with that raw data I need to do some computations. Initially,I want to start with trying small computations.

So Which tool is helpful to do computations inside cloud such as doing some math and finding whether the number is even number or not ,giving some input and performing some algorithm and finding the result? I just want to pick data from my table residing in DynamoDB and do these computations.I saw Redshift in google but its little expensive,will it be possible to use that and load the data from dynamoDB to redshift and do the math operations or there any better alternate options? Will you please share me any links that will help me to start with?

Thank you very much .

Answer 1

In DynamoDB, you can only increment and decrement numeric attributes using the + (plus) and - (minus) operators in the SET action of an UpdateExpression in update_item or the ADD action if only both; the existing attribute is a number and the value is also a number.

Otherwise, you should perform your desired math operations against attribute values before updating them in DynamoDB.

Note on ADD :

If you use ADD to increment or decrement a number value for an item that doesn't exist before the update, DynamoDB uses 0 as the initial value. Similarly, if you use ADD for an existing item to increment or decrement an attribute value that doesn't exist before the update, DynamoDB uses 0 as the initial value.

For example:

response = client.update_item(
    ExpressionAttributeNames={
        '#C': 'Count'
    },
    ExpressionAttributeValues={
        ':val': {
            'N': '1'
        }
    },
    Key={
        'ItemId': {
            'S': 'BC3AB494-EDD8-4F47-B80F-32ACA92D8C5C'
        }
    },
    ReturnValues='ALL_NEW',
    TableName='MyTable',
    UpdateExpression='SET #C = #C - :val'
)

print(response)

See also: Incrementing and Decrementing Numeric Attributes .