Validate user input in AppSync DynamoDB Resolvers
Solution 1:
I can't find a nice way of doing this in GraphQL, but you can do it easily in VTL using either $util.validate or $util.error (see the AWS documentation). They both have the same result of adding an item to the errors array.
Here's a demo of $util.validate:
https://mappingtool.dev/app/appsync/bee55bd607e2166091451e7a7959318e
Here's a demo of $util.error:
https://mappingtool.dev/app/appsync/006d6c05e8bb7257c6cebce34494994c