AppSync DynamoDB Resolvers with update conditions

There is a resolver's code
```
{
"version": "2017-02-28",
"operation": "UpdateItem",
"key": {
"PK": $util.dynamodb.toDynamoDBJson($ctx.args.input.PK),
"SK": $util.dynamodb.toDynamoDBJson($ctx.args.input.SK),
},

## Set up some space to keep track of things you're updating **
#set( $expNames = {} )
#set( $expValues = {} )
#set( $expSet = {} )
#set( $expAdd = {} )

## Increment "ActualLimit"
$!{expAdd.put("ActualLimit", ":actuallimit")}
$!{expValues.put(":actuallimit", { "N" : $context.arguments.input.ActualLimit } )}

## Continue building the update expression, adding attributes you're going to ADD **
#if( !${expAdd.isEmpty()} )
#set( $expression = "${expression} ADD" )
#foreach( $entry in $expAdd.entrySet() )
#set( $expression = "${expression} ${entry.key} ${entry.value}" )
#if ( $foreach.hasNext )
#set( $expression = "${expression}," )
#end
#end
#end

## Finally, write the update expression into the document, along with any expressionNames and expressionValues **
"update" : {
"expression" : "${expression}"
#if( !${expNames.isEmpty()} )
,"expressionNames" : $utils.toJson($expNames)
#end
#if( !${expValues.isEmpty()} )
,"expressionValues" : $utils.toJson($expValues)
#end
},

"condition" : {
"expression" : "LimitDate = :expectedLimitDate",
"expressionValues" : {
":expectedLimitDate" : $util.dynamodb.toDynamoDBJson($context.arguments.input.LimitDate)
}
}

}
```
and mutation:
```
mutation MyMutation {
update(input: {PK: "pk1", SK: "sk1", ActualLimit:0, LimitDate: "YYYY-MM-DD"}) {
ActualLimit CreatedAt LimitDate
}
}
```
where PK - primary key, SK - sorted key, ActualLimit is integer value, LimitDate is string value.

My question is how to write the code if I need two cases:
- If there is a record with same `LimitDate` value then need to increment `ActualLimit` for value from the mutation and SET fields
- If there is no record with same `LimitDate` value then need to just SET fields(like LimitDate)

e.g.:
have record in DynamoDb: `{ "PK": "pk1", "SK": "sk1", "ActualLimit": 10, "LimitDate": "2022-06-08"}`
case 1:
```
mutation MyMutation {
update(input: {PK: "pk1", SK: "sk1", ActualLimit:2, LimitDate: "2022-06-08"}) {
ActualLimit CreatedAt LimitDate
}
}
```
then have record in DynamoDb: `{ "PK": "pk1", "SK": "sk1", "ActualLimit": 12, "LimitDate": "2022-06-08"}`

case 2:
```
mutation MyMutation {
update(input: {PK: "pk1", SK: "sk1", ActualLimit:1, LimitDate: "2022-06-19"}) {
ActualLimit CreatedAt LimitDate
}
}
```
then have record in DynamoDb: `{ "PK": "pk1", "SK": "sk1", "ActualLimit": 1, "LimitDate": "2022-06-19"}`

How to do that?
thanks.

Start with the AppSync DynamoDB UpdateItem resolver and the MyMutation examples in the issue, then review AppSync conditional writes and DynamoDB update expressions. Verify both supplied cases against records keyed by PK and SK; done means matching LimitDate values increment ActualLimit while different values replace the relevant fields.

Written by the indexing model from the issue text.