Search code examples
pythonamazon-dynamodbboto3

Can Boto3's DynamoDB "update_item" method handle native python objects?

I'm currently using boto3 to get and put items into DynamoDB. I can get and put like this:

def get_item(key):
    # key is a dict like {"partitionkey": "abc", "sortkey": "123"}
    table = boto3.resource("dynamodb").Table(DYNAMO_TABLE)
    response = table.get_item(Key=key)
    return response.get("Item")

def put_item(key, item):
    # item is a dict of data to store, e.g. {"name": "uhoh", "size": 100}
    table = boto3.resource("dynamodb").Table(DYNAMO_TABLE)
    return table.put_item(Item={**key, **item})

This works great! I pass Python dictionary to the put_item function, and I get a Python dictionary back when I call get_item. I don't need to do any of the DynamoDB encoding stuff1, it just works.

Now I'm looking at introducing update_item in addition to put_item. It seems I cannot pass these Python types to the update_item method in the same way; when I try I get

table.update_item(Key=my_key, UpdateExpression="SET #X = :x",
    ExpressionAttributeNames={"#X": "my_property"},
    ExpressionAttributeValues={":x": somedict})

botocore.exceptions.ParamValidationError: Parameter validation failed: Unknown parameter in ExpressionAttributeValues.:x: "my_key", must be one of: S, N, B, SS, NS, BS, M, L, NULL, BOOL

My question: is there a way to have the update_item handle this transformation for me the same as put_item does? Or is there a utility that can transform back and forth between these two formats? At this point I'm thinking update_item isn't worth the extra effort and lines of code.

1 Transformation from [{"my_key": "my_value"}] to {"L": [{"M": {"my_key": {"S": "my_value"}}}]} is handled auto-magically!

Solution

  • Yes. You can use the Resource Client to use native JSON dicts. Have a read of this blog which outlines the differences and shows how to achieve it:

    https://aws.amazon.com/blogs/database/exploring-amazon-dynamodb-sdk-clients/