get.mjs

import { DynamoDB } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocument } from "@aws-sdk/lib-dynamodb";
import { createResponse } from '/opt/nodejs/sample-layer/utils.mjs';

const dynamodb = DynamoDBDocument.from(new DynamoDB({}));

const TABLE_NAME = process.env.TABLE_NAME;
const DDB_GSI_NAME = process.env.DDB_GSI_NAME;

let corsHeaders = {
    'Access-Control-Allow-Origin': process.env.CORS_ORIGIN,
    'Access-Control-Allow-Credentials': true,
};

export const handler = async (event) => {
    return new Promise(async (resolve) => {
        // to query the object, we require either the dataOwner and objectId (base table query),
        // or the objectId (index query).
        let getParams;
        let queryParams;
        if (event.queryStringParameters.dataOwner) {
            // if we have the partition and sort keys, we can "get" the object directly
            getParams = {
                TableName: TABLE_NAME,
                Key: {
                    "dataOwner": event.queryStringParameters.dataOwner,
                    "objectId": event.pathParameters.objectId
                }
            };
            // or we can query the base table
            queryParams = {
                TableName: TABLE_NAME,
                KeyConditionExpression: 'dataOwner = :owner_id and objectId = :obj_id',
                ExpressionAttributeValues: {
                    ':owner_id': event.queryStringParameters.dataOwner,
                    ':obj_id': event.pathParameters.objectId
                }
            };
        } else {
            // if we don't have both partition and sort keys, we must query using an
            // appropriate secondary index
            console.log(`querying table index`);
            queryParams = {
                TableName: TABLE_NAME,
                IndexName: DDB_GSI_NAME,
                KeyConditionExpression: 'objectId = :obj_id',
                ExpressionAttributeValues: { ':obj_id': event.pathParameters.objectId }
            };
        }

        try {
            const result = getParams ?
                await dynamodb.get(getParams) :
                await dynamodb.query(queryParams);
            resolve(createResponse({
                "statusCode": 200,
                "headers": corsHeaders,
                "body": result
            }));
        } catch (err) {
            console.error(err);
            resolve(createResponse({
                "statusCode": 500,
                "headers": corsHeaders,
                "body": {
                    "success": false,
                    "reason": "an unexpected error occurred",
                    "error": err
                }
            }));
        }
    });
}