Stream

The Stream class is designed to process DynamoDB streams and convert them into corresponding Dynamode entity instances.

This simplifies the process of handling DynamoDB streams and allows you to work with Dynamode entities directly.

info

DynamoDB streams of type KEYS_ONLY are not supported in Dynamode.

Stream constructor - new Stream(Entity)

Every stream has to be initialized with data from a DynamoDB stream record. The Stream class constructor takes a DynamoDB Record and initializes a Stream instance.

import Stream from 'dynamode/stream';

const stream = new Stream(dynamoDBRecord);

Stream properties

The Stream class has the following properties:

• streamType: The type of the stream. It can be one of the following: newImage, oldImage, or both.
• operation: The operation that was performed on the entity. It can be one of the following: insert, modify, or remove.
• newImage: The new entity image after the operation. Instance of the entity class.
• oldImage: The old entity image before the operation. Instance of the entity class.
• entity: The entity class that the stream corresponds to.

stream.isEntity(entity)

Description

A method to check if the stream entity corresponds to the provided entity class. It also narrows down the type of the stream entity to the provided entity class.

Arguments

entity: Entity: The entity class you want to check the stream entity against.

Returns

Returns true if it's the same entity type, otherwise false.

Examples

Let's say you have a stream that you want to check if it corresponds to the User entity. This way you can easily check if the stream entity is a User entity and work with it accordingly.

const stream = new Stream(dynamoDBRecord);

// Check that the stream refers to the User entity
if (stream.isEntity(User)) { 
  // images are narrowed down here (Stream<Entity> -> Stream<User>)
  const newUser = stream.newImage;
  const oldUser = stream.oldImage;
  
  // Do logic based on custom logic
  if(oldUser.username !== newUser.username && newUser.age > 18) {
    // Do something
  }
}

Support for aws-lambda

The Stream class is designed to work with AWS Lambda functions that process DynamoDB streams. Here is an example of how you can use the Stream class in a Lambda function.

import type { Context, DynamoDBStreamEvent } from 'aws-lambda';
import Stream from 'dynamode/stream';

async function itemStream(event: DynamoDBStreamEvent, context: Context): void {
  const stream = new Stream(event.Records[0]);

  // Update list progress when an item is created
  if (stream.isEntity(List)) {
    if (stream.operation === 'insert' && stream.newImage) {
      await ListManager.update(List.getPrimaryKey(stream.newImage.listId), {
        increment: {
          'progress.checked': 1,
        },
      });
    }
  }
}