DynamoDB UpdateExpression Functionality

Feature Requests
1

Currently DynamoDB does not offer the functionality natively within n8n to update an existing item and add additional attributes. I think this would be very helpful to use as a datastore if needed.

UpdateExpression would need to be added to allow for items to be updated during an upsert.

2

I’ve addressed this for the time being with an AWS Lambda (see code below) as well as the sample event that allows me to update the table contents without a complete overwrite. It admittedly feels a little hacky, but hopefully it’s enough of a solution to help others in the foreseeable future.

import boto3
from boto3.dynamodb.conditions import Key
from botocore.exceptions import ClientError

def lambda_handler(event, context):
    # Extract the table name, key, and updates from the event
    table_name = event['table_name']
    key = event['key']
    updates = event['updates']  # Expecting a list of dictionaries with 'attribute_name', 'value_to_add', and 'value_type'

    # Initialize a DynamoDB client
    dynamodb = boto3.resource('dynamodb')
    table = dynamodb.Table(table_name)

    # Build the update expression and attribute values dynamically
    update_expression_parts = []
    expression_attribute_values = {}
    expression_attribute_names = {}

    for i, update in enumerate(updates):
        attr = update['attribute_name']
        val = update['value_to_add']
        value_type = update.get('value_type', 'numeric')  # Assume numeric if value_type is not provided
        placeholder = f"#attr{i}"
        value_placeholder = f":val{i}"

        if value_type == 'numeric':
            update_expression_parts.append(f"{placeholder} = if_not_exists({placeholder}, :zero) + {value_placeholder}")
            expression_attribute_values[':zero'] = 0  # Set the initial value to 0 for numeric attributes
        else:
            update_expression_parts.append(f"{placeholder} = if_not_exists({placeholder}, :empty) + {value_placeholder}")
            expression_attribute_values[':empty'] = ''  # Set the initial value to an empty string for string attributes

        expression_attribute_values[value_placeholder] = val
        expression_attribute_names[placeholder] = attr

    final_update_expression = "SET " + ", ".join(update_expression_parts)

    # Update the item in DynamoDB
    try:
        response = table.update_item(
            Key=key,
            UpdateExpression=final_update_expression,
            ExpressionAttributeNames=expression_attribute_names,
            ExpressionAttributeValues=expression_attribute_values,
            ReturnValues='UPDATED_NEW'
        )
        return response
    except ClientError as e:
        print(e.response['Error']['Message'])
        return e.response['Error']['Message']

Sample Input Event

updates = [
    {"attribute_name": "Prompt Tokens", "value_to_add": 427, "value_type": "numeric"},
    {"attribute_name": "Completion Tokens", "value_to_add": 108, "value_type": "numeric"},
    {"attribute_name": "Total Tokens", "value_to_add": 535, "value_type": "numeric"},
    {"attribute_name": "Log", "value_to_add": "New log entry", "value_type": "string"}
]```

If anyone has questions, feel free to reach out!
3

still i think it’s best n8n “DynamoDB official” node should support the proper UPSERT without remove those fields which are not requested. Million thanks!

4

+1 for upsert