aws-dynamodb-es-cqrs · ES/CQRS using AWS DynamoDB 


- Events
- Events are described by AggregateEvent
(ULID-based eventId, aggregateName, aggregateId, aggregateVersion,
actorId).
- Aggregate metadata:
- AggregateMeta with id, version,
actorId, optional updatedAt.

- Reducing events to aggregates (Event Sourcing)
- Generic reducer: reduceEvents
applies a sequence of AggregateEvent to
produce an aggregate state.
- Domain reducer example (BlogPost):
blogPostReducer uses type guards
(isNamedEvent) and assertions (assertAggregateEvent) to evolve state
from events.

- Commands (write side)
- Commands validate current state and produce new events:
- Create: createBlogPostCommand
- Publish:
publishBlogPostCommand
- Update title:
updateBlogPostTitleCommand
- Concurrency and existence are enforced using:
- ConflictError and
NotFoundError
- Version checks against the loaded aggregate before emitting the next
event.

- Persistence (event store + aggregate projection)
- DynamoDB persistence is transactional to keep aggregate and event store in
sync:
- persistDynamoDB performs a
TransactWrite that:
- Upserts the aggregate row with optimistic concurrency:
- New aggregate: attribute_not_exists(aggregateId) (version 1).
- Update: #version = :prevVersion and sets updatedAt.
- Writes the event into the events table.
- Aggregate unmarshalling for reads:
unmarshallAggregate.
- Event queries:
- List an aggregate’s events:
listAggregateEventsDynamoDB
- Parse DynamoDB Streams records back into events:
extractEventsFromDynamoDBEvent

- Queries (read side)
- Read the current aggregate projection:
- Example (BlogPost):
- findBlogPostByIdDynamoDB.
- listBlogPostsDynamoDB.

Setup

Install the dependencies:

``bash
npm ci
`

Tests

The test folder contains an example aggregate (a blog post), and
operations that manipulate it, which demonstrate how the key components of this
implementation work with separate read/write components demonstrating create,
read aggregate, list events, and optimistic concurrency.

Install DynamoDB (local)

`bash
wget https://s3.eu-central-1.amazonaws.com/dynamodb-local-frankfurt/dynamodb_local_latest.zip
unzip dynamodb_local_latest.zip -d ./dynamodb_local_latest
`

Start it in background:

`bash
java -Djava.library.path=./dynamodb_local_latest/DynamoDBLocal_lib -jar ./dynamodb_local_latest/DynamoDBLocal.jar -sharedDb -inMemory &
`

Run the tests:

`bash
npm test
``