Auction Service CRUD Operations

Middleware

Middleware are functions that run either before or after your Lambda handler.

We will be using middy, a middleware engine for AWS Lambda.

import middy from '@middy/core';
import httpJsonBodyParser from '@middy/http-json-body-parser';
import httpEventNormalizer from '@middy/http-event-normalizer';
import httpErrorHandler from '@middy/http-error-handler';

const myLambda = (event, context) => {
  /* code here */
};

export const handler = middy(myLambda)
  .use(httpJsonBodyParser())
  .use(httpEventNormalizer())
  .use(httpErrorHandler());

Common middlewares

GET Request: Scanning

If you recall, scanning get items by looking through an entire table, which is inefficient. But it's good to know how to do it using the AWS SDK.

const result = await dynamoDb.scan({ TableName: 'MY_TABLE_NAME' }).promise();
console.log(result.Items); // array of all items in table

Note: If you're adding a new GET endpoint using scan, you'll need to update the Serverless framework in a few places:

• Add a lambda function for the endpoint

• Include the operation type dynamodb:Scan in the IAM config

GET Request: Querying by Key

Querying is more efficient as it can make use of primary partition keys when looking for items.

const result = await dynamoDb
  .get({
    TableName: 'MY_TABLE_NAME',
    Key: { id: 'my-id' },
  })
  .promise();
console.log(result.Item);

Similarly, you want to update the serverless.yml:

• Include a lambda function for the new endpoint

• Include operation type dynamodb:GetItem in the IAM config

PATCH Request: Updating

To update an item, you query by key and provide the properties you want to change. Here's the rough syntax:

const params = {
  TableName: 'MY_TABLE_NAME',
  Key: { id: 'MY_ID' },
  // Special language for updating
  UpdateExpression: 'set firstName = :firstName',
  // Attributes you want to update
  ExpressionAttributeValues: {
    ':firstName': 'Daniel',
  },
  // What you want to return (in this case the updated item)
  ReturnValues: 'ALL_NEW',
};

const result = await dynamoDb.update(params).promise();
console.log(result.Attributes); // { firstName: "Daniel" }