DynamoDB Stream Router

The router can be configured with a set of handlers. A handler has the concept of rules and message handlers. For each DynamoDB stream record that matches the set of rules the message handlers will be returned from the route function.

Note, this is meant to be used on Dynamo Streams with a StreamViewType of NEW_AND_OLD_IMAGES

Installation

npm install dynamodb-stream-router --save

Usage

Before any of the handler rules are evaluated against the DynamoDB stream records. The stream records are converted to a stream Item with the following shape:

export interface DynamoStreamItem<T> {
   readonly newRec?: Partial<T>;
   readonly oldRec?: Partial<T>;
   readonly streamEventName: StreamEventName;
 }
 
 export enum StreamEventName {
   INSERT = "INSERT",
   MODIFY = "MODIFY",
   REMOVE = "REMOVE"
 }

This item is then checked against each handlers set of rules. If all rules match the handler is returned as a matched handler.

Example

Given the following stream record:

const cartCreatedEvent: DynamoDBStreamEvent = {
   Records: [
     {
       eventID: "687541e3494dc8de9ff8d1f64b69bba1",
       eventName: "INSERT",
       eventVersion: "1.1",
       eventSource: "aws:dynamodb",
       awsRegion: "us-east-1",
       dynamodb: {
         ApproximateCreationDateTime: 1579295785,
         Keys: {
           cartId: {
             S: "11abc7c8-4907-4203-a690-8652a6237680"
           },
           customerId: {
             S: "21abc7c8-4907-4203-a690-8652a6237682"
           }
         },
         NewImage: {
           testAttribute: {
             S: "test"
           },
           cartId: {
             S: "d20c2a9f-9e54-47c8-b15b-3825ab18a9ea"
           },
           customerId: {
             S: "21abc7c8-4907-4203-a690-8652a6237682"
           }
         },
         SequenceNumber: "4217800000000000074376631",
         SizeBytes: 317,
         StreamViewType: "NEW_AND_OLD_IMAGES"
       },
       eventSourceARN:
         "arn:aws:dynamodb:us-east-1:647096707908:table/CartTable-1CTA7CIJVD6OW/stream/2020-02-08T06:31:13.980"
     }
   ]
 };

it would be converted to:

 interface TestItem {
   cartId: string;
   customerId: string;
   testAttribute: string;
 }     

 const dynamoStreamItem: DynamoStreamItem<TestItem> = {
    streamEventName: "INSERT",
    newRec: {
      cartId: "d20c2a9f-9e54-47c8-b15b-3825ab18a9ea",
      customerId: "21abc7c8-4907-4203-a690-8652a6237682",
      testAttribute: "test"
    },
    oldRec: {}
  };

We can then create a handler for all insert events:

 const insertItemHandler: DynamoMessageRouteHandler<TestItem> = {
        rules: [
           (streamItem: DynamoStreamItem<TestItem>) => { 
              return streamItem.streamEventName === "INSERT';
           }
        ],
        messageHandlers: [
           (streamItem: DynamoStreamItem<TestItem>) => { 
               console.log(`matched handler, cartId: ${streamItem.newRec.cartId}`);
           }
        ]
  };

Now we setup the router with all the configured handlers.

const configuredStreamRouter = matchedStreamHandlers([
   insertItemHandler, deleteItemHanlder
]);

const matchedHandlers = configuredStreamRouter(dynamoDBStreamEvent)