Background
As a part of my personal growth plan and work commitments, I am working on the AWS Certified Developer - Associate certification using the Linux Academy platform. In one of the lab exercises that I was doing on DynamoDB, there were requirements for updating DynamoDB attribute using SDK and perform conditional updates and atomic counters on the tables. Being what I am, I did not use the examples they had provided, but created by own table to create a database of books I own and proceeded to create my own attribute names for the items.
The problem
As it happened, I created attributes like book-title, book-author, book-price, etc. which in itself is not a problem. However, the lab exercise had me perform the item updates using the BOTO3 Python SDK which got me excited to learn new things. I used the example files that the trainer had provided and modified it to suit my environment and ran the script.
UpdateExpression='SET book-price = :val',
ExpressionAttributeValues={
':val': {'N': '15.37'},
':currval': {'N': '0'}
},
ConditionExpression='book-price = :currval',
ReturnValues="ALL_NEW"To my dismay, I started encountering errors.
Traceback (most recent call last):
File "conditional_write.py", line 18, in
ReturnValues="ALL_NEW"
File "/usr/local/lib/python3.7/site-packages/botocore/client.py", line 316, in _api_call
return self._make_api_call(operation_name, kwargs)
File "/usr/local/lib/python3.7/site-packages/botocore/client.py", line 626, in _make_api_call
raise error_class(parsed_response, operation_name)
botocore.exceptions.ClientError: An error occurred (ValidationException) when calling the UpdateItem operation: Invalid UpdateExpression: Syntax error; token: "-", near: "book-price" The Solution
I reviewed my code to ensure that I had not introduced any bugs myself. After ensuring that I had not introduced any bugs by adding new attributes to an item without any dashes and running the script successfully, I starting practicing my Google-Fu. There I found this awesome post on stackoverflow along with a link to official AWS documentation. The official documentation however only talks about a dot being a special character and it doesn't list a dash (-). After following the instructions from the stackoverflow post, my new code looked like this:
UpdateExpression='SET #bp = :val',
ExpressionAttributeValues={
':val': {'N': '15.37'}, # Make sure we keep this line the same
':currval': {'N': '0'} # What was the current value?
},
ExpressionAttributeNames={
"#bp": "book-price"
},
ConditionExpression='#bp = :currval',
ReturnValues="ALL_NEW"And once I implemented this code it all started working correctly. I have left a feedback for the AWS documentation team and hopefully they will update the documentation. I just want to make sure that all the cases are at listed and documented so that developers and wannabes like me are not stuck.
