Appsync Resolver UpdateItem ignore null args? - amazon-web-services

Question

I am doing this in my Appsync Resolver:
{
"version" : "2017-02-28",
"operation" : "UpdateItem",
"key" : {
"pk" : { "S" : "Container" },
"id" : { "S" : "${ctx.args.id}" }
},
"update" : {
"expression" : "SET #name = :name, description = :description",
"expressionNames": {
"#name" : "name"
},
"expressionValues": {
":name" : { "S": "${context.arguments.name}" },
":description" : { "S": "${context.arguments.description}" },
}
}
}
But sometimes I may not pass in both name and description. How would I make it not SET those columns when those args are null?

Answer 1

All you need to do is to create your own SET expression with condition checked based on your need. Below expression check if any argument is null or empty, I don't want to update it.
#set( $expression = "SET" )
#set( $expValues = {} )
## NAME
#if( !$util.isNullOrEmpty(${context.arguments.name}) )
#set( $expression = "${expression} name = :name" )
$!{expValues.put(":name", { "S" : "${context.arguments.name}" })}
#end
## DESCRIPTION
#if( !$util.isNullOrEmpty(${context.arguments.description}) )
#if( ${expression} != "SET" )
#set( $expression = "${expression}," )
#end
#set( $expression = "${expression} description = :description" )
$!{expValues.put(":description", { "S" : "${context.arguments.description}" })}
#end
{
"version" : "2017-02-28",
"operation" : "UpdateItem",
"key" : {
"pk" : { "S" : "Container" }
"id" : { "S" : "${context.arguments.id}" }
},
"update" : {
"expression" : "${expression}",
"expressionValues": $util.toJson($expValues)
}
}
Hope it is useful!

Answer 2

This is very much possible. You just have to add a simple if statement to check if the value is there. A parallel example can be seen in the docs here: https://docs.aws.amazon.com/appsync/latest/devguide/tutorial-dynamodb-resolvers.html
Specifically, that example (below) uses the application of optional arguments into a list operation.
{
"version" : "2017-02-28",
"operation" : "Scan"
#if( ${context.arguments.count} )
,"limit": ${context.arguments.count}
#end
#if( ${context.arguments.nextToken} )
,"nextToken": "${context.arguments.nextToken}"
#end
}
Just applying that if's null check should work for you.