DynamoDB: No way to combine multiple ConditionExpression

[SamStephens]

Describe the feature

According to https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.OperatorsAndFunctions.html it's possible to combine multiple conditions using AND and OR. However, from my reading of https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/dynamodb/table/update_item.html and https://boto3.amazonaws.com/v1/documentation/api/latest/reference/customizations/dynamodb.html#boto3.dynamodb.conditions.Attr, it is only possible to specify a single condition using the update_item operation.

Use Case

I have an attribute I want to update, but not if the update will decrease the attributes value. The attribute is not necessarily present. So I need my conditional expression to be attribute not exists OR attribute value < my value.

It appears the API supports this conditional expression, but not this SDK.

Proposed Solution

• Add a super class for boto3.dynamodb.conditions.Attr, maybe boto3.dynamodb.conditions.Condition.
• Make the ConditionExpression parameter a boto3.dynamodb.conditions.Condition.
• Give boto3.dynamodb.conditions.Condition three methods, And, Or, and Not, that each do the obvious thing.

Under this scheme, my ConditionExpression would be

ConditionExpression = Condition().Or(Attr(attribute_name).not_exists(), Attr(attribute_name).lt(updated_value))

Other Information

The only way I can see to workaround this is two conditional updates - firstly with not_exists, and then if the check fails because the attribute exists, try the update again with lt.

Acknowledgements

• [X] I may be able to implement this feature request
• [ ] This feature might incur a breaking change

SDK version used

1.34.76

Environment details (OS name and version, etc.)

Ubuntu (Windows Subsystem for Linux)

[crh23]

Do the classes defined as follows fit your use-case? https://github.com/boto/boto3/blob/096e45841545f24bbd572a62504cc0dbb62e6b07/boto3/dynamodb/conditions.py#L158-L238 You can write expressions like ConditionExpression = Or(Attr(attribute_name).not_exists(), Attr(attribute_name).lt(updated_value))

I'm not sure if they are documented anywhere

[SamStephens]

@crh23 thanks, this is exactly what I needed.

I've closing this issue as support is present, and replacing it with an issue for the missing documentation.

[github-actions[bot]]

This issue is now closed. Comments on closed issues are hard for our team to see. If you need more assistance, please open a new issue that references this one.