Graceful handling of ConditionCheckFailedException with DynamoDB - amazon-web-services

Question

When using ConditionExpression in a DynamoDB request, and the condition is not met, the entire request will fail. I am using conditional updates, and the fact that ConditionCheckFailedException doesn't contain any information about which condition failed is giving me a hard time.
For example consider this scenario: There's an item in a table like this:
{
state: 'ONGOING'
foo: 'FOO',
bar: 'BAR'
}
I then want to update this item, changing both foo and state:
ExpressionAttributeValues: {
:STATE_FINISHED: 'FINISHED',
:FOO: 'NEW FOO'
},
UpdateExpression: 'SET state=:STATE_FINISHED, foo=:FOO',
However, my application has a logical transition order of states, and to prevent concurrency issues where two requests concurrently modify an item and causing an inconsistent state, I add a condition to make sure only valid transitions of state are accepted:
ExpressionAttributeValues: {
:STATE_ONGOING: 'ONGOING'
},
ConditionExpression: 'state = :STATE_ONGOING'
This e.g. prevents two concurrent requests from modifying state into FINISHED and CANCELLED at the same time.
This is all fine when there's only one condition; if the request fails I know it was because an invalid state transition and I can choose whether to just fail the request, or to make a new request that only modifies FOO, whatever makes sense in my application. But if I have multiple conditions in one request, it seems impossible to find out which particular condition failed, which means I need to fail the entire request or divide it into multiple separate requests, updating one conditional value at a time. This can however raise new concurrency issues.
Has anyone found a decent solution to a similar problem?
Ideally what I'd want is to be able to make a UpdateExpression that modifies a certain attribute conditionally, otherwise ignoring it, or by using a custom function that returns the new value based on the old value and the suggested updated value, similar to an SQL UPDATE with an embedded SELECT .. CASE .... Is anything like this possible?
Or, is it at least possible to get more information out of a ConditionalCheckFailedException (such as which particular condition failed)?

Answer 1

As you mentioned, the DynamoDB doesn't provide granular level error message if there are multiple fields available on ConditionalExpression. I am not addressing this part of the question in my answer.
I would like to address the second part i.e. returning the old/new value.
The ReturnValues parameter can be used to get the desired values based on your requirement. You can set one of these values to get the required values.
New value - should already be available
Old value - To get old value, you can either use UPDATED_OLD or ALL_OLD
ReturnValues: NONE | ALL_OLD | UPDATED_OLD | ALL_NEW | UPDATED_NEW,
ALL_OLD - Returns all of the attributes of the item, as they appeared
before the UpdateItem operation.
UPDATED_OLD - Returns only the
updated attributes, as they appeared before the UpdateItem operation.
ALL_NEW - Returns all of the attributes of the item, as they appear
after the UpdateItem operation.
UPDATED_NEW - Returns only the updated
attributes, as they appear after the UpdateItem operation.