Update attributes of DynamoDB table item

Question

While defining my DynamoDB table, I selected filename as the unique attribute or primary key. In this function, I want to modify some columns of the entry with a particular filename. I tried this after following another SO answer:

def update_item_in_db(filename, archive_path):
    table = dynamodb.Table(dynamodb_table_name)
    try:
        logger.info(f'Updating dynamo table for filename: {filename}')
        response = table.update_item(
            Key={'filename': filename},
            AttributeUpdates={
                'archive_path': archive_path,
                'archived_on': datetime.today().strftime('%Y-%m-%d-%H:%M:%S')
            },
        )
    except Exception as e:
        raise Exception(f"Unable to insert filename into dynamodb: {e}") 
    return response

but I get an error that:

Parameter validation failed:\nInvalid type for parameter AttributeUpdates.archive_path, value: archive/100-ff0-uat/1591282803734/issues_1591282803734.zip, type: <class 'str'>, valid types: <class 'dict'>\nInvalid type for parameter AttributeUpdates.archived_on, value: 2021-11-21-15:06:46, type: <class 'str'>, valid types: <class 'dict'>",

Then I also tried:

        response = table.update_item(
            {
                'filename': filename,
                'archive_path': archive_path,
                'archived_on': datetime.today().strftime('%Y-%m-%d-%H:%M:%S')
            }
        )

but then I get the following error:

 "Unable to insert filename into dynamodb: update_item() only accepts keyword arguments.",

What's the correct syntax to update an item?

Note that I only want to UPDATE/MODIFY and not delete and re-insert.

score 0 · Accepted Answer · answered Nov 21 '21 at 16:54

The first approach uses a deprecated syntax. The second one is closer to what you want to do.

Something like this should work:

from datetime import datetime

import boto3

dynamodb = boto3.resource("dynamodb")

def update_item_in_db(filename, archive_path):
    table = dynamodb.Table(dynamodb_table_name)

    table.update_item(
        Key={
            "filename": filename
        },
        UpdateExpression="SET #archive_path = :archive_path, #archived_on = :archived_on",
        ExpressionAttributeNames={
            "#archive_path": "archive_path",
            "#archived_on": "archived_on"
        },
        ExpressionAttributeValues={
            ":archive_path": archive_path,
            ":archived_on": datetime.today().strftime('%Y-%m-%d-%H:%M:%S')
        }
    )

The ExpressionAttributeNames and ExpressionAttributeValues allow you to use reserved keywords in the UpdateExpression, that's why they're commonly used.

(I didn't run the code, there may be typos.)

Update attributes of DynamoDB table item

1 Answers1