AWS appsync w/ Lambd function backend, GraphQL gives unexpected repsonce to Query - aws-lambda

Question

What follows is all in the AWS console. My lambda function defines deletePost
case "deletePost":
var id = event.arguments.id;
callback(null, {id:-1,author:"me",title:"title"}); //note, regardless of what your args are right now it is returning id:-1
break;
My schema is
type Mutation {
...
deletePost(id: ID!): Post!
}
type Post {
id: ID!
author: String!
title: String
}
and my graphiQL query is
mutation DeletePost{
deletePost(id: 3){
id
}
}
For some reason it just parrots id=3 back to me when i've hard coded id as -1? If I ask for author or title to be return in my query I don't get them back at all.
Update full lambs fxn. Just a slightly modified version of the template that is provided with the aws appSync docs.
exports.handler = (event, context, callback) => {
console.log("Received event {}", JSON.stringify(event, 3));
var posts = { //in memory array store (simulates DB)
"1": {"id": "1", "title": "First book", "author": "Author1"},
"2": {"id": "2", "title": "Second book", "author": "Author2"},
"3": {"id": "3", "title": "Third book", "author": "Author3"},
"4": {"id": "4", "title": "Fourth book", "author": "Author4"},
"5": {"id": "5", "title": "Fifth book", "author": "Author5"} };
console.log("Got an Invoke Request: "+event.field);
switch(event.field) {
case "getPost":
var id = event.arguments.id;
callback(null, posts[id]);
break;
case "updatePost":
posts[event.arguments.id]=event.arguments;
console.log(posts);
callback(null, event.arguments);
break;
case "deletePost":
var id = event.arguments.id;
//delete posts[event.arguments.id];
callback(null, {id:-1,author:"me",title:"tits"});
break;
case "allPosts":
var values = [];
for(var d in posts){
values.push(posts[d]);
}
callback(null, values);
break;
case "addPost":
var id = event.arguments.id;
posts[id]=event.arguments;
console.log(posts);
callback(null, event.arguments);
break;
case "addPostErrorWithData":
var id = event.arguments.id;
var result = posts[id];
// attached additional error information to the post
result.errorMessage = 'Error with the mutation, data has changed';
result.errorType = 'MUTATION_ERROR';
callback(null, result);
break;
default:
callback("Unknown field, unable to resolve" + event.field, null);
break;
}
};
Resolvers. For the most part just pass the data straight through.
#request mapping
{
"version" : "2017-02-28",
"operation": "Invoke",
"payload": {
"field": "addPost",
"arguments": $util.toJson($context.arguments)
}
}
#responce mapping
$util.toJson($context.result)

Answer 1

It's hard to know without seeing all of the Lambda function and also your resolver templates. From the above code I'm going to guess you used this tutorial as a starting point: https://docs.aws.amazon.com/appsync/latest/devguide/tutorial-lambda-resolvers.html
Assuming you're passing back the result in the response template, like $util.toJson($context.result), then the issue is most likely with the structure of the callback in your Lambda function
let result = {"id" :-1, "author":"me", "title":"title"}
callback(null, result);
Essentially you need to pass back a result object for it to be seen in the $context object and converted as a GraphQL JSON response to the caller.