Now that we created a note and saved it to our database. Let’s add an API to retrieve a note given its id.

Add the Function

Create a new file get.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, callback) {
  const params = {
    TableName: "notes",
    // 'Key' defines the partition key and sort key of the item to be retrieved
    // - 'userId': Identity Pool identity id of the authenticated user
    // - 'noteId': path parameter
    Key: {
      userId: event.requestContext.identity.cognitoIdentityId,
      noteId: event.pathParameters.id
    }
  };

  try {
    const result = await dynamoDbLib.call("get", params);
    if (result.Item) {
      // Return the retrieved item
      callback(null, success(result.Item));
    } else {
      callback(null, failure({ status: false, error: "Item not found." }));
    }
  } catch (e) {
    callback(null, failure({ status: false }));
  }
}

This follows exactly the same structure as our previous create.js function. The major difference here is that we are doing a dynamoDbLib.call('get', params) to get a note object given the noteId and userId that is passed in through the request.

Configure the API Endpoint

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

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

Make sure that this block is indented exactly the same way as the preceding create block.

This defines our get note API. It adds a GET request handler with the endpoint /notes/{id}.

Test

To test our get note API we need to mock passing in the noteId parameter. We are going to use the noteId of the note we created in the previous chapter and add in a pathParameters block to our mock. So it should look similar to the one below. Replace the value of id with the id you received when you invoked the previous create.js function.

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

{
  "pathParameters": {
    "id": "578eb840-f70f-11e6-9d1a-1359b3b22944"
  },
  "requestContext": {
    "identity": {
      "cognitoIdentityId": "USER-SUB-1234"
    }
  }
}

And we invoke our newly created function.

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

The response should look similar to this.

{
  statusCode: 200,
  headers: {
    'Access-Control-Allow-Origin': '*',
    'Access-Control-Allow-Credentials': true
  },
  body: '{"attachment":"hello.jpg","content":"hello world","createdAt":1487800950620,"noteId":"578eb840-f70f-11e6-9d1a-1359b3b22944","userId":"USER-SUB-1234"}'
}

Next, let’s create an API to list all the notes a user has.