Using DynamoDB, I know I can specify a conditional expression to control updates, for example, using attribute_not_exists() to prevent overwriting an existing item. However, is there any way to check the result of this? I.e. if there was indeed an existing item and the create failed, I'd like to know that so I can return an error code in my HTTP response. However, looking at the documentation in Boto3, by default put_item returns nothing, so I'm unsure of how I'd be able to monitor the success of the operation. Anyone found a way to do this?
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2 Answers
To provide a code example
import boto3
from botocore.exceptions import ClientError
dynamodb = boto3.client('dynamodb')
try:
response = dynamodb.put_item(
TableName='my-table',
Item={
"MyPartitionKey": {
"S": 'some-unique-value'
}
},
ConditionExpression="attribute_not_exists(MyPartitionKey)",
)
print('this worked!')
except ClientError as e:
if e.response['Error']['Code'] == 'ConditionalCheckFailedException':
print('This was not a unique key')
else:
print('some other dynamodb related error')
Comments
Found it, ConditionalCheckFailedException is thrown. Disappointed the docs don't mention this, other kinds of exceptions are detailed in the boto3 docs, but not this one!
1 Comment
maafk
Agreed that this should be better documented. I learned this from this SO answer