Now let’s create an API that allows a user to update a note with a new note object given its id.

Add the Function

Create a new file update.js and paste the following code

import * as dynamoDbLib from "./libs/dynamodb-lib";
import { success, failure } from "./libs/response-lib";

export async function main(event, context) {
  const data = JSON.parse(event.body);
  const params = {
    TableName: "notes",
    // 'Key' defines the partition key and sort key of the item to be updated
    // - 'userId': Identity Pool identity id of the authenticated user
    // - 'noteId': path parameter
    Key: {
      userId: event.requestContext.identity.cognitoIdentityId,
      noteId: event.pathParameters.id
    },
    // 'UpdateExpression' defines the attributes to be updated
    // 'ExpressionAttributeValues' defines the value in the update expression
    UpdateExpression: "SET content = :content, attachment = :attachment",
    ExpressionAttributeValues: {
      ":attachment": data.attachment || null,
      ":content": data.content || null
    },
    // 'ReturnValues' specifies if and how to return the item's attributes,
    // where ALL_NEW returns all attributes of the item after the update; you
    // can inspect 'result' below to see how it works with different settings
    ReturnValues: "ALL_NEW"
  };

  try {
    const result = await dynamoDbLib.call("update", params);
    return success({ status: true });
  } catch (e) {
    return failure({ status: false });
  }
}

This should look similar to the create.js function. Here we make an update DynamoDB call with the new content and attachment values in the params.

Configure the API Endpoint

Open the serverless.yml file and append the following to it.

  update:
    # Defines an HTTP API endpoint that calls the main function in update.js
    # - path: url path is /notes/{id}
    # - method: PUT request
    handler: update.main
    events:
      - http:
          path: notes/{id}
          method: put
          cors: true
          authorizer: aws_iam

Here we are adding a handler for the PUT request to the /notes/{id} endpoint.

Test

Create a mocks/update-event.json file and add the following.

Also, don’t forget to use the noteId of the note we have been using in place of the id in the pathParameters block.

{
  "body": "{\"content\":\"new world\",\"attachment\":\"new.jpg\"}",
  "pathParameters": {
    "id": "578eb840-f70f-11e6-9d1a-1359b3b22944"
  },
  "requestContext": {
    "identity": {
      "cognitoIdentityId": "USER-SUB-1234"
    }
  }
}

And we invoke our newly created function from the root directory.

$ serverless invoke local --function update --path mocks/update-event.json

The response should look similar to this.

{
  statusCode: 200,
  headers: {
    'Access-Control-Allow-Origin': '*',
    'Access-Control-Allow-Credentials': true
  },
  body: '{"status":true}'
}

Next we are going to add an API to delete a note given its id.