Aws Appsync $util.error: data and errorInfo always null - amazon-web-services

Question

I am playing with AWS AppSync. I am trying to output some error details when the request fails using the $util.error() helper (Documented here) in my resolver's response mapping template. No matter what I do, I am not able to get AppSync to output the data and errorInfo fields in the error output.
Here is the Lambda I have.
exports.handler = (event, context, callback) => {
callback(null, {
data: {
name: "Test",
},
errorMessage: "Some error Message",
errorType: "SomeErrorType",
errors: {
"foo": "bar",
"bazz": "buzz",
}
})
};
As you can see, it is pretty much straight forward. I just return an object with the data, errors, errorMessage and errorType properties.
And here is my response mapping template
$utils.error($context.result.errorMessage, $context.result.errorType, $context.result.data, $context.result.errors)
Again, pretty much straight forward. I just throw an error directly using the fields coming from the Lambda.
But when I execute the query, I get this:
{
"data": {
"myField": null
},
"errors": [
{
"path": [
"myField"
],
"data": null,
"errorType": "SomeErrorType",
"errorInfo": null,
"locations": [
{
"line": 2,
"column": 3,
"sourceName": null
}
],
"message": "Some error Message"
}
]
}
As you can see, the errorType and message fields get populated correctly, but not the errorInfo and data ones.
Am I missing something? Why isn't this working ?
I also tried hardcoding the parameters of $util.error in the template. I got the same result...

Answer 1

As the documentation states, Note: data will be filtered based on the query selection set. So you need to return data that matches the selection set.
So, for a basic schema that looks like:
type Post {
id: ID!
title: String!
}
type Query {
simpleQuery: Post
}
schema {
query: Query
}
And a query:
query {
simpleQuery {
title // Note this selection set
}
}
And a response mapping template:
$utils.error($context.result.errorMessage, $context.result.errorType, $context.result.data, $context.result.errors)
With a Lambda code:
exports.handler = (event, context, callback) => {
callback(null, {
data: {
title: "Test", // The same selection set
},
errorMessage: "Some error Message",
errorType: "SomeErrorType",
errors: {
"foo": "bar",
"bazz": "buzz",
}
})
};
It will return:
{
"data": {
"badOne": null
},
"errors": [
{
"path": [
"badOne"
],
"data": {
"title": "Test"
},
"errorType": "SomeErrorType",
"errorInfo": null,
"locations": [
{
"line": 8,
"column": 3,
"sourceName": null
}
],
"message": "Some error Message"
}
]
}

Answer 2

For the errorInfo, you will need to update the template version to 2018-05-29.
See my answer here: https://stackoverflow.com/a/53495843/2724342