How to use direct lambda resolver in appsync? - amazon-web-services

Question

I have tried to use direct lambda resolver with appsync schema and trying to get items from dynamoDB table but getting error. I can see the results in cloudwatch log but I can't get the result in query page.
One other question that my post has #hasMany comments and comments #belongsTo post how can I get the comments directly with post using direct lambda resolver. I think I have to do a separate query for comments? Appsync pipeline is good at getting queries but it is very very slow.
My lambda function:
const AWS = require("aws-sdk");
const dynamo = new AWS.DynamoDB.DocumentClient();
exports.handler = async (event) => {
const response = await dynamo.get({
TableName: "Post-xxxxxxxxxxxxx",
Key: {
id: event.arguments.id
}
}).promise();
console.log(response); // I can see the response here in cloudwatch.
return JSON.stringify(response);
};
My query :
query MyQuery {
getPost(id: "xxxxxx-xxxxx-xxxx-xxxxxxx") {
id
title
}
}
Query result:
{
"data": {
"getPost": null
},
"errors": [
{
"path": [
"getPost",
"id"
],
"locations": null,
"message": "Cannot return null for non-nullable type: 'ID' within parent 'Post' (/getPost/id)"
},
{
"path": [
"getPost",
"title"
],
"locations": null,
"message": "Cannot return null for non-nullable type: 'String' within parent 'Post' (/getPost/title)"
}
]
}