> For the complete documentation index, see [llms.txt](https://notes.danfitz.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://notes.danfitz.com/javascript/serverless-bootcamp/c-auction-service-crud-operations.md).

# 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.

```js
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.

```js
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.

```js
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:

```js
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" }
```