AWS AppSync returns null on query where lambda function actually returns result

Question

I have a AppSync API that is linked to a lambda function as data source, the lambda function is calling another API to retrieve data from Database.

However after I setup the schema and resolver as well as the lambda function, it kept return me null result despite I have the actual result in my lambda function. (I printed it in logs so I can see it)

Here is my schema:

scalar AWSDateTime

type Event implements Node {
    appId: String!
    description: String
    eventName: String!
    id: String!
    nodeId: ID!
    ts: AWSDateTime!
}

input EventCondition {
    appId: String
    description: String
    eventName: String
    id: String
    ts: AWSDateTime
}

type EventsConnection {
    nodes: [Event!]!
    totalCount: Int!
}

enum EventsOrderBy {
    APP_ID_ASC
    APP_ID_DESC
    DESCRIPTION_ASC
    DESCRIPTION_DESC
    EVENT_NAME_ASC
    EVENT_NAME_DESC
    ID_ASC
    ID_DESC
    NATURAL
    PRIMARY_KEY_ASC
    PRIMARY_KEY_DESC
}

interface Node {
    nodeId: ID!
}

type Query implements Node {
    event(id: String!): Event
    eventByNodeId(nodeId: ID!): Event
    events(
        condition: EventCondition,
        first: Int,
        last: Int,
        offset: Int,
        orderBy: [EventsOrderBy!]
    ): EventsConnection
    node(nodeId: ID!): Node
    nodeId: ID!
    query: Query!
}

Here is my resolver request mapping for events, I hardcoded it so I can test:

{
    "version" : "2017-02-28",
    "operation": "Invoke",
    "payload": {
        "fieldName": "events",
        "parentTypeName": "query",
        "selectionSetGraphQL": "{\n nodes\n {\n  id\n  appId\n  eventName\n }\n}"
    }
}

Here is my response mapping template:

$util.toJson($context.result)

I expect it directly returns what Lambda Function return which is an object, but it is not. Here is what my lambda function have:

    const client = new GraphQLClient(eventsGraphQLURI, { headers: {} })

    client.request(request).then(
        (data) => {
            response = data;
            console.log(`Result: ${JSON.stringify(response)}`)
        })
        .catch((error) => {
            console.log(`Error Occurred: ${error}`)
    })
    
    return response;

When I check the logs, this is what the API return to my Lambda Function:

    {
        "events": {
            "nodes": [
                {
                    "id": "1e8601cf-a740-4146-a9b7-a38201a89eab",
                    "appId": "2fa39c1e-5b40-4a77-bab3-d22a79f051a7",
                    "eventName": "TemperatureDetection"
                },
                {
                    "id": "2645538",
                    "appId": "cc472578-2389-40ea-8525-a2b86fea23c4",
                    "eventName": "xxx"
                }
            ]
        }
    }

However when I run query on AppSync console, this is what it returns:

{
  "data": {
    "events": null
  }
}

Is there anything that I have done wrong so it will not recognized? When I go and check the logs of the AppSync, there is not any response.context log. All I have for response after the request in the log is as below image:

Deeply appreciates if anyone could help with this, I struggled for like two days on this. Thank you!

Sivvie Lim · Accepted Answer · 2022-09-02 01:28:43Z

1

Okay totally overlook on my side. If anyone was wondering the same issue, check the lambda function, it needs to be async and also return the response in a callback.

Here are my new lambda function code that works:

exports.handler = async (event, context, callback) => {
    const client = new GraphQLClient(eventsGraphQLURI, { headers: {} })

    await client.request(request).then(
        (data) => {
            response = data;
            console.log(`Result: ${JSON.stringify(response)}`)
        })
        .catch((error) => {
            console.log(`Error Occurred: ${error}`)
    })
    
    callback(null, response);
}

answered Sep 2, 2022 at 1:28

Sivvie Lim

1,3984 gold badges27 silver badges54 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Jamie Marshall Over a year ago

why must it be async?

Collectives™ on Stack Overflow

AWS AppSync returns null on query where lambda function actually returns result

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related