AWS Javascript Resolver UpdateItem: The provided key element does not match the schema

Question

I am using the javascript resolver to update an item on the database but am getting this error:

The provided key element does not match the schema.

Resolver request:

export function request(ctx) {
  const { username } = ctx.arguments.input;
  const { identity } = ctx;

  const now = util.time.nowISO8601();
  const user = `USER#${identity.claims.sub}`

  return {
    operation: "UpdateItem",
    key: util.dynamodb.toMapValues({ pk: user }),
    update: {
      expression: 'SET #username = :username',
      expressionNames: { '#username': 'username' },
      expressionValues: { ':username': { S: username } },
    }
}

Request function evaluation from AppSync cloudwatch:

{
    "logType": "RequestFunctionEvaluation",
    "fieldName": "updateUsername",
    "resolverArn": "arn:aws:appsync:us-xxxx-2:xxxxx:apis/xxxxx/types/Mutation/resolvers/updateUsername",
    "functionName": "update_username_function",
    "fieldInError": false,
    "evaluationResult": {
        "operation": "UpdateItem",
        "key": {
            "pk": {
                "S": "USER#118b6520-80c1-7074-0ed5-616bf57fbc3b"
            }
        },
        "update": {
            "expression": "SET #username = :username",
            "expressionNames": {
                "#username": "username"
            },
            "expressionValues": {
                ":username": {
                    "S": "dfgdf"
                }
            }
        }
    },
    "parentType": "Mutation",
    "path": [
        "updateUsername"
    ],
    "requestId": "172905a5-a810-400d-9e65-55bdc8a23964",
    "context": {
        "arguments": {
            "input": {
                "username": "dfgdf"
            }
        },
        "prev": {
            "result": []
        },
        "stash": {},
        "outErrors": []
    },
    "errors": [],
    "graphQLAPIId": "ivxudb2wxfda7htbuk64eje66e",
    "functionArn": "arn:aws:appsync:us-east-2:637453376396:apis/xxxxxx/functions/xxxxxx"
}

Response evaluation:

...
"error": {
        "message": "The provided key element does not match the schema (Service: DynamoDb, Status Code: 400, Request ID: L7GLI66HRS7H7GPA4TN3RT2F1FVV4KQNSO5AEMVJF66Q9ASUAAJG)",
        "type": "DynamoDB:DynamoDbException"
    },
...

Following docs here: https://docs.aws.amazon.com/appsync/latest/devguide/tutorial-dynamodb-resolvers-js.html

import { util } from '@aws-appsync/utils';

export function request(ctx) {
  const { id, direction } = ctx.arguments;
  const field = direction === 'UP' ? 'ups' : 'downs';

  return {
    operation: 'UpdateItem',
    key: util.dynamodb.toMapValues({ id }),
    update: {
      expression: `ADD ${field} :plusOne, version :plusOne`,
      expressionValues: util.dynamodb.toMapValues({ ':plusOne': 1 }),
    },
  };
}

export function response(ctx) {
  return ctx.result;
}

What would be causing this to throw this error? I have confirmed that the pk in my database is of name "pk" and type string.

Answer 1

Figured out that my issue was a missing sk in my key. I thought the sk was optional, but that's only in the case where you may not have an sk.

So it becomes: key: util.dynamodb.toMapValues({pk: user, sk: "CONFIG"})