AWS DynamoDB Transaction issues (Python) - python-3.x

Question

I am trying to update 2 tables transactionally. first table is called CUSTOMER_TABLE, second is called CUSTOMER_JOB_TABLE.
for the first table, I create a new row if it doesnt exist. if it does exist i add to the currentProcessedCount column the value from this specific process. for the second table, i always create a new row. the 2 updates need to be transactional. i get the following error and I cant figure out what the reason is. Can someone help?
Response:
{
"errorMessage": "An error occurred (TransactionCanceledException) when calling the TransactWriteItems operation: Transaction cancelled, please refer cancellation reasons for specific reasons [ValidationError, None]",
"errorType": "TransactionCanceledException",
"stackTrace": [
" File \\"/var/task/app.py\\", line 149, in lambda_handler\\n c_table_response = update_customer_table(customer_id, customer_monthly_limit, number_of_rows,\\n",
" File \\"/var/task/app.py\\", line 226, in update_customer_table\\n response = dynamodb_client.transact_write_items(\\n",
" File \\"/opt/python/botocore/client.py\\", line 316, in _api_call\\n return self._make_api_call(operation_name, kwargs)\\n",
" File \\"/opt/python/botocore/client.py\\", line 635, in _make_api_call\\n raise error_class(parsed_response, operation_name)\\n"
]
}
below is my method for the call
import boto3
dynamodb_client = boto3.client('dynamodb')
# grab static env variable
CUSTOMER_ID = os.environ['CUSTOMER_ID']
BUCKET_NAME = os.environ['BUCKET_NAME']
CUSTOMER_TABLE_NAME = os.environ['CUSTOMER_TABLE_NAME']
CUSTOMER_JOB_TABLE_NAME = os.environ['CUSTOMER_JOB_TABLE_NAME']
def update_customer_table(customer_id, customer_monthly_limit, number_of_rows, year_month, uuid, date_time, batch_no):
response = dynamodb_client.transact_write_items(
TransactItems=[
{
'Update': {
'TableName': CUSTOMER_TABLE_NAME,
'Key': {
'PK': {'S': customer_id},
'SK': {'N': str(year_month)},
},
'ExpressionAttributeNames': {
'#ml': "MonthlyLimit",
'#cpc': "currentProcessedCount"
},
'ExpressionAttributeValues': {
':ml': {'N': str(customer_monthly_limit)},
':cpc': {'N': str(number_of_rows)}
},
'UpdateExpression': "SET #ml = :ml ADD #cpc :cpc"
}
},
{
'Put': {
'TableName': CUSTOMER_JOB_TABLE_NAME,
'Item': {
'PK': {'S': f'{customer_id}_{uuid}'},
'SK': {'N': str(year_month)},
'CustomerId': {'S': customer_id},
'UUID': {'S': uuid},
'StartDateTime': {'N': date_time.strftime('%Y%m%d%H%M')},
'NumberOfSplitFiles': {'N': str(batch_no - 1)},
'TotalRowCount': {'N': str(number_of_rows)}
}
}
}
]
)
return response

Answer 1

This is a problem, not sure if it's the only one.
'ExpressionAttributeValues': {
':ml': {'N': str(customer_monthly_limit)},
':cpc': {'N': str(number_of_rows)}
},
'UpdateExpression': "SET #ml = :mlv ADD #cpc :cpc"
:mlv doesn't match :ml