Storing optional attributes in DynamoDB's putItem via step functions - amazon-dynamodb

Question

I have defined a state machine in AWS step functions and one of my states is storing an item to DynamoDB
...
"Store item": {
"End": true,
"Type": "Task",
"Resource": "arn:aws:states:::dynamodb:putItem",
"Parameters": {
"Item": {
"foo": {
"S.$": "$.data.foo"
},
"bar": {
"S.$": "$.data.bar"
},
"baz": {
"S.$": "$.data.baz"
},
},
"TableName": "nrp_items"
}
},
...
The problem starts from the fact that baz property is optional, ie not exist in some cases.
On those cases, the putItem task fails:
An error occurred while executing the state 'Store item' (entered at the event id #71). > The JSONPath '$.data.baz' specified for the field 'S.$' could not be found in the input
My backup plan is to use a lambda to perform that type of operation, but can I do it directly using the putItem task in steps function?
I was wondering if:
Is possible to somehow inject via JSONPath my whole $.data item to the "Item" property, something like:
...
"Store item": {
"End": true,
"Type": "Task",
"Resource": "arn:aws:states:::dynamodb:putItem",
"Parameters": {
"Item": "$.data",
"TableName": "nrp_items"
}
},
...
OR
2) Define that the baz property is optional

Answer 1

TL;DR We can deal with optional variables with a "Variable": "$.baz", "IsPresent": true Choice condition to handle no-baz cases.
The Amazon States Language spec does not have optional properties: Step Functions will throw an error if $.baz does not exist in the input. We can avoid undefined paths by inserting a two-branch Choice State, one branch of which handles baz-exists cases, the other no-baz cases. Each branch continues with a Pass State that reworks the data input into dynamo-format Item syntax, using Parameters. The put-item task's "Item.$": "$.data" (as in your #1) contains only foo-bar when baz is not defined, but all three otherwise.
{
"StartAt": "HasBazChoice",
"States": {
"HasBazChoice": {
"Type": "Choice",
"Choices": [
{
"Variable": "$.baz",
"IsPresent": true,
"Next": "MakeHasBazItem"
}
],
"Default": "MakeNoBazItem"
},
"MakeHasBazItem": {
"Type": "Pass",
"Parameters": {
"data": {
"foo": { "S.$": "$.foo"},
"bar": { "S.$": "$.bar"},
"baz": { "S.$": "$.baz"}
}
},
"Next": "PutItemTask"
},
"MakeNoBazItem": {
"Type": "Pass",
"Parameters": {
"data": {
"foo": {"S.$": "$.foo"},
"bar": {"S.$": "$.bar"}
}
},
"Next": "PutItemTask"
},
"PutItemTask": {
...
"Parameters": {
"TableName": "my-table",
"Item.$": "$.data"
}
},
}
}
If you have more than one optional field, your lambda backup plan is the better option - the above workaround would become unwieldy.